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Page 1: 268580

Vibration SensorsVibration Sensors

Power Supply Units

Sensor Housings

Cables and Connectors

Accessories

Installation/Mounting

SKF Reliability Systems

Page 2: 268580

Introduction/Selection 1Introduction ……………………………………………………………………… 1

The Critical Choice ……………………………………………………………… 1

Selection of Vibration Sensors …………………………………………………... 1

Piezoelectric Sensors …………………………………………………………….. 2

Choosing An Industrial Sensor ………………………………………………….. 3

Primary Sensor Considerations ………………………………………………….. 3

Environmental Requirements ……………………………………………………. 4

Electrical Powering Requirements ………………………………………………. 5

Other Sensor Types ……………………………………………………………… 6

Vibration Sensor Descriptions 7CMSS 786M Dual Sensor-Accelerometer and SEE™ Sensor, Piezoelectric ……. 7

CMSS 793T-3 Multifunction Sensor: Acceleration and Temperature …………... 8

CMSS 797T-1 Low Profile, Industrial IsoRing® Piezoelectric

Accelerometer with Internal Temperature Sensor ………………………….. 9

CMSS 793L Low Frequency Piezoelectric Accelerometer ……………………..11

CMSS 797L Low Profile, Low Frequency, Industrial IsoRing®

Piezoelectric Accelerometer ………………………………………………. 12

CMSS 793V Piezoelectric Velocity Transducer ………………………………...14

CMSS 797V Industrial IsoRing® Velocity Accelerometer ……………………... 15

CMSS 85 Series High Temperature Inductive Velocity Transducer ……………16

CMSS 603A-1 and CMSS 603A-3 Power Supply Units ………………………..18

Vibration Sensor Installation 19Vibration Sensor Installation Considerations …………………………………... 19

Vibration Sensor Mounting Requirements 22Mounting Requirements ………………………………………………………... 22

Sensitivity Validation …………………………………………………………... 23

Summary ……………………………………………………………………….. 23

Vibration Sensor Mounting Accessories 24Mounting Hardware …………………………………………………………………... 24

CMSS 60139-4 Probe Tip (Stinger) ………………………………………. 24

CMSS 30168700 Threaded Mounting Stud (1/4–28 to 1/4–28) …………...24

CMSS 30168701 Adaptor Stud (1/4–28 to M8) …………………………...24

CMSS 30168703 Adaptor Stud (1/4–28 to M6) …………………………...24

CMSS 30205300 Mounting Stud (1/4–28 to 10-32) ……………………… 24

CMSS 910M Cementing Stud With 1/4–28 Male ………………………… 24

CMSS 910F Cementing Stud With 1/4–28 Female ………………………..24

CMSS 10876700 Captive Screw ………………………………………….. 24

Magnetic Mounting Hardware ………………………………………………………. 24

CMSS 908-RE Rare Earth Magnetic Base Flat Bottom …………………... 24

Magnetic Bases For Curved Surfaces ……………………………………………… 25

CMSS 908-MD Medium Duty Magnetic Base …………………………… 25

CMSS 908-HD Heavy Duty Magnetic Base ……………………………… 25

Quick Connect/Disconnect Sensor Mounting Pads ……………………………… 25

CMSS 910QDP-1 Stud Mounting Pad ……………………………………. 25

CMSS 910QDP-2 Cement Mounting Pad ………………………………… 25

CMSS 910QDB-1 Sensor Base …………………………………………… 25

CMSS 50042300 Case Mounted Transducer Housing …………………………. 26

70003010 Mounting Kit for Seismic Transducers ………………………………27

CMSS 30266101 Vibration Sensor Housings ………………………………….. 28

Hazardous Area Information 29Area General Information ……………………………………………………….29

Agency Approvals ……………………………………………………………… 29

VibrationSensors

Table ofContents

i

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VibrationSensors

Table ofContents

ii

Technical Notes–Reprints 30Piezoelectric Materials for Vibration Sensors–The Technical Advantages

of Piezoceramics Versus Quartz …………………………………………... 30

Sensors Solutions for Industrial Cooling Towers and Process Cooler Fans …… 31

Accelerometers Measure Slow Speed Rollers and Detect High Frequencies ….. 32

Glossary 33

Conversion Charts 39

Sensor Selection Checklist 40

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Vibration Sensors Introduction / Selection 1

Frequency

VelocityAcceleratio

n

Displacement

Am

plitu

de

CONSTANT DISPLACEMENT

Frequency

Displacement

Am

plitu

de

CONSTANT VELOCITY

Velocity

Accele

ratio

n

Frequency

Displacement

Am

plitu

de

CONSTANT ACCELERATION

Acceleration

Velocity

IntroductionDespite the advances made in vibration monitoring andanalysis equipment, the selection of sensors and the waythey are mounted on a machine remain critical factors indetermining the success of any monitoring program.Money saved by installing inferior sensors is not aprudent investment since the information provided aboutthe machine of interest often is not accurate or reliable.Poor quality sensors can easily give misleading data or, insome cases, cause a critical machine condition to becompletely overlooked.

The Critical ChoiceThe various rotating machine operating conditionsconcerning temperature, magnetic field, g range,frequency range, electromagnetic compatibility (EMC)and electrostatic discharge (ESD) conditions and thevarious parameters measured in the multi-parameterapproach necessitates the need for a variety of sensors.Without a proper sensor to supply the critical operatinginformation, the machine can be operating in a mosthazardous condition to both the machine as well as thepersonnel operating the machine. SKF in partnershipwith one of the worlds leading industrial sensormanufacturers has developed and can provide the epitomeof industrial sensors, accelerometers and velocitytransducers for your critical machine monitoring.

The key to proper machine monitoring however is theproper choice of sensor for the particular installation.Without the proper sensor, the best instrumentation andsoftware available will not provide the definitiveinformation on which to make a “sound engineeringdetermination” regarding the mechanical operatingcondition or deficiencies of the machine.

The ability to monitor more than one machine parameterwith the same sensor can give added insight to machineperformance at a more economical cost than usingseparate sensors for each (ESD) conditions and thevarious parameters measured in the multi-parameterapproach necessitates the (ESD) conditions and thevarious parameters measured in the multi-parameter

Figure 1. The relationship of acceleration and displacement and velocity.

approach necessitates the parameter. Such an approachcan be classified as Multi-Parameter Monitoring.

Selection of Vibration SensorsThe three parameters representing motion detected byvibration monitors are displacement, velocity, andacceleration. These parameters can be measured by avariety of motion sensors and are mathematically related(displacement is the first derivative of velocity andvelocity is the first derivative of acceleration). Selectionof a sensor proportional to displacement, velocity oracceleration depends on the frequencies of interest and thesignal levels involved.

Figure 1 shows the relationship between velocity anddisplacement and acceleration. Sensor selection andinstallation is often the most critical determining factor inaccurate diagnoses of machinery condition.

DISPLACEMENT SENSORS

Eddy current probes are non-contact sensors primarilyused to measure shaft vibration, shaft/rotor position andclearance. Also referred to as displacement probes, eddycurrent probes are typically applied on machines utilizingsleeve/journal bearings. They have excellent frequencyresponse with no lower frequency limit and can also beused to provide a trigger input for phase-relatedmeasurements.

SKF monitors also have the ability to take the output ofan accelerometer and double integrate to obtain a relativedisplacement; however, except in very special cases, it isinadvisable because of significant low frequencyinstability associated with the integration process. Eddycurrent probe systems remain the best solution for shaftposition measurements.

(Please refer to SKF Condition Monitoring publicationCM2004 for guidance on the selection, application andinstallation of Eddy Current Probe Systems.)

VELOCITY SENSORS

Velocity sensors are used for low to medium frequencymeasurements. They are useful for vibration monitoring

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2 Vibration Sensors Introduction / Selection

and balancing operations on rotatingmachinery. As compared toaccelerometers, velocity sensors havelower sensitivity to high frequencyvibrations. The mechanical design ofthe velocity sensor; an iron coremoving within a coil in a limitedmagnetic field, no clipping of thegenerated signal occurs, but smoothsaturation.

In an accelerometer with ICPelectronics, sensor resonanceexcitation can cause saturation andclipping of the electronic circuitgenerating false low frequencycomponents. Integrating to velocityfrom the acceleration signal leads tolarge low frequency components.Resonance damping circuits betweensensor element and amplifier canminimize that effect.

Traditional velocity sensors are of a mechanical designthat uses an electromagnetic (coil and magnet) system togenerate the velocity signal. Recently, hardierpiezoelectric velocity sensors (internally integratedaccelerometers) have gained in popularity due to theirimproved capabilities and more rugged and smaller sizedesign. A comparison between the traditional coil andmagnetic velocity sensor and the modern piezoelectricvelocity sensor is shown in Table 1.

The electromagnetic (Inductive) velocity sensor does havea critical place in the proper sensor selection. Because ofits high temperature capability it finds wide application ingas turbine monitoring and is the sensor of choice bymany of the major gas turbine manufacturers.

The high temperature problems for systems usingaccelerometers can also be solved by splitting sensor andelectronics (charge amplifiers). The sensor can have hightemperature ranges up to +1,112°F (+600°C).

Some methods of investigating bearing defects and gearproblems may require a higher frequency range andbecause the signals are generated by impact, thesensitivity should be lower. By the same means if theuser is using the SKF “Enveloping Technique” then justthe opposite is applicable.

ACCELEROMETERS

Piezoelectric accelerometers having a constant signal overa wide frequency range, up to 20 kHz's, for a givenmechanical acceleration level, are very useful for all typesof vibration measurements.

Acceleration integrated to velocity can be used for lowfrequency measurements. Acceleration signals in the highfrequency range added with various signal processingtechniques like ACC ENV, or HFD are very useful forbearing and gear measurements.

Table 1. Electromagnetic Velocity Sensors vs. Piezoelectric Velocity Sensors.

The basic acceleration sensor has a good signal to noiseratio over a wide dynamic range.

They are useful for measuring low to very highfrequencies and are available in a wide variety of generalpurpose and application specific designs. Thepiezoelectric sensor is versatile, reliable and the mostpopular vibration sensor for machinery monitoring.

When combined with vibration monitors capable ofintegrating from acceleration to velocity, accelerometerscan be a useful component in a Multi-ParameterMonitoring Program. The user is, therefore, able todetermine both velocity and acceleration values for thesame machine point with a single sensor.

SEE™ SENSORS

As a complementary technology to the sensors discussedabove, SKF has developed and patented sensors based onSEE Technology. SEE (Spectral Emitted Energy) isused to detect acoustic emission signals in the range of250–350 kHz, well beyond the range of conventionalvibration sensors. Such acoustic emission signals aregenerated by stress-type defects such as metal-to-metalimpacts and wear. This can happen when rolling over alocal defect or a partical or when there is wear in a drysliding contact (metal-to-metal contact). For example,when a rolling element of an anti-friction bearing breaksthrough its lubrication film and slides SEE sensors areable to detect the condition. The user then has theopportunity to take proactive steps in order to preventfurther damage.

Piezoelectric SensorsAccelerometers operate on the piezoelectric principal: acrystal generates a low voltage or charge when stressed asfor example during compression. (The Greek root word“piezein” means “to squeeze”.) Motion in the axial

Coil and Magnet PiezoelectricCharacteristic Velocity Sensor Velocity Sensor

Flat Frequency Response20–1,500 Hz Yes Yes2–5,000 Hz No Yes

Phase Fidelity2–5,000Hz Acceptable Excellent

Reduced Noise at

Higher Frequencies No Yes

Linearity Good Good

Mounting in Any Orientation Sensor Dependent Yes

Temperature Limitation > +707°F (+375°C) +248°F (+120°C)

EMI* Resistance Acceptable Excellent

Mechanical Durability Good Excellent

*EMI–Electro Magnetic Interference

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Vibration Sensors Introduction / Selection 3

chosen for the application. The user who addressesapplication and noise floors specific questions willbecome more familiar with sensor requirements and bemore likely to select the proper sensor for the application.

Typical questions include:

• What is the expected maximum vibration level?

• What type of vibration (sinusoidal, pulsed, mixed)?

• What is the frequency range of interest?

• Does the machine use sleeve/journal or rollingelement bearings?

• What is the running speed of the machine?

• What is the temperature range required?

• Are any corrosive chemicals or detergents present?

• Is the atmosphere combustible?

• Are intense acoustic or electromagnetic fieldspresent?

• Is electrostatic discharge (ESD) present in the area?

• Is the machinery grounded?

Other questions must be answered about the connector,cable, and associated electronics:

• What cable lengths are required?

• Is armored cable required?

• To what temperatures will the cable be exposed?

• Does the sensor require a splash-proof connector orintegrated cable connector?

• What other instrumentation will be used?

• What are the power supply requirements?

Primary Sensor ConsiderationsTwo of the main parameters of a piezoelectric sensor arethe sensitivity and the frequency range. In general, mosthigh frequency sensors have low sensitivities and,

Figure 2. Typical frequency response curves for various

direction stresses the crystal due to the inertial force of themass and produces a signal proportional to acceleration ofthat mass. This small acceleration signal can be amplifiedfor acceleration measurements or converted(electronically integrated) within the sensor into avelocity or displacement signal. This is commonlyreferred as the ICP (Integrated Circuit Piezoelectric) typesensor. The piezoelectric velocity sensor is more ruggedthan a coil and magnet sensor, has a wider frequencyrange, and can perform accurate phase measurements.

Most industrial piezoelectric sensors used in vibrationmonitoring today contain internal amplifiers.

PIEZOELECTRIC MATERIALS: CERAMIC vs.QUARTZ

The two basic piezoelectric materials used in vibrationsensors today are synthetic piezoelectric ceramics andquartz. While both are adequate for successful vibrationsensor design, differences in their properties allow fordesign flexibility. For example, modern “tailored”piezoceramic materials have better charge sensitivity thannatural piezoelectric quartz materials. Most vibrationsensor manufacturers now use piezoceramic materialsdeveloped specifically for sensor applications. Specialformulations yield optimized characteristics to provideaccurate data in extreme operating environments. Theexceptionally high output sensitivity of piezoceramicmaterial allows the design of sensors with increasedfrequency response when compared to quartz.

Much has been said of the thermal response of quartzversus piezoceramics. Both quartz and piezoceramicsexhibit an output during a temperature transient(pyroelectric effect) when the material is not mountedwithin a sensor housing. Although this effect is muchlower in quartz than in piezoceramics, when properlymounted within a sensor housing the elements are isolatedfrom fast thermal transients. The difference in materialsthen becomes insignificant. The dominant thermal signalsare caused by metal case expansion strains reaching thebase of the crystal. These erroneous signals are then afunction of the mechanical design rather than sensingmaterial (quartz or piezoceramic). Proper sensor designsisolate strains and minimize thermally induced signals.(See section on "Temperature Range" page 4.)

High quality piezoceramic sensors undergo artificialaging during the production process. This ensures stableand repeatable output characteristics for long termvibration monitoring programs. Theoretical stabilityadvantages of quartz versus ceramic designs areeliminated as a practical concern.

Development of advanced piezoceramics with highersensitivities and capability to operate at highertemperatures is anticipated.

Choosing An Industrial SensorWhen selecting a piezoelectric industrial vibration sensormany factors must be considered so that the best sensor is

Sen

siti

vity

, dB

re

1V/g

1 10 1 k 10 k 100 k

Frequency, Hz

20

0

–10

–30

10

–20

1

–40

0.3

25 kHz40 kHz

high sensitivity 1V/g

medium sensitivity 100mV/g

low sensitivity 10mV/g

15 kHz

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4 Vibration Sensors Introduction / Selection

– NOTE –

Sensors with lower frequency ranges tend to have lower electronic noisefloors. Lower noise floors increase the sensor’s dynamic range and may

be more important to the application than the high frequencymeasurements.

The following should be considered when determining thehigh and low frequency responses of a sensor.

In order to select the frequency range of a piezoelectricsensor, it is necessary to determine the frequencyrequirements of the application. It is also important toconsider the type of analyzing techniques that will beapplied and the types of events the user is interested toanalyze. For example, determining imbalance andmisalignment can be done with a sensor having a lowerfrequency range and a high sensitivity.

The required frequency range is often already knownfrom vibration data collected from similar systems orapplications. The plant engineer may have enoughinformation on the machinery to calculate the frequenciesof interest. Sometimes the best method to determine thefrequency content of a machine is to place a test sensor(in the direction of the shaft centerline) at variouslocations on the machine and evaluate the data collected.

In industrial machinery, frequencies related to imbalance,misalignment, looseness are typically lower than 1,000Hz (60,000 cpm).

Frequencies and harmonics related to bearing and geardefects are a few hundred Hz and higher. The exceptionis the cage frequency which is approximately one half theshaft speed. As demonstrated in the following example, ifthe running speed of a rotating shaft is known, the highestfrequency of interest is normally a multiple of the productof the running speed and the geometry of the bearingsupporting the shaft.

Environmental RequirementsTEMPERATURE RANGE

Sensors must be able to survive temperature extremes ofthe application environment. The sensitivity variationversus temperature must be acceptable to themeasurement requirement.

Temperature transients (hot air, steam, or oil splash) cancause metal case expansion resulting in erroneous outputduring low frequency measurements (< 5 Hz). In suchcases a protective sensor housing should be considered inorder to limit the effect of temperature induced transients.Some of these inherent errors may also be overcome withthe use of monitors equipped with envelope band passfilters and enveloping techniques in the vibration monitorcircuitry.

HUMIDITY

All SKF vibration sensors are sealed to prevent the entryof high humidity and moisture. In addition, integralcables, splash-proof cable connectors and jackets areavailable to withstand high humidity or wet environments.Contact SKF for recommendations on your application.

conversely, most high sensitivity sensors have lowfrequency ranges. The dependence of inertia on massgoverns this relationship. As the mass increases thesensitivity is also increased; however, the usablefrequency range is reduced since the sensor more quicklyapproaches its resonance frequency, shown in Figure 2. Itis therefore necessary to compromise between thesensitivity and the frequency response.

Another criteria is: "Is the sensor used for bearing defectmonitoring?" Because rolling over a defect can generatehigh g-levels (excitation of the sensor resonancefrequency) up to 100 g peak. Therefore it is sometimeswise to select 10 mV/g or 30 mV/g as sensor sensitivity.

THE SENSITIVITY RANGE

The sensitivity of industrial accelerometers typicallyrange between 10 and 100 mV/g; higher and lowersensitivities are also available. To choose the correctsensitivity for an application, it is necessary to understandthe range of vibration amplitude levels to which thesensor will be exposed during measurements.

As a rule of thumb, if the machine produces highamplitude vibrations (greater than 10 g RMS) at themeasurement point, a low sensitivity (10 mV/g) sensor ispreferable. If the vibration is less than 10 g RMS, higherthan 10 mV/g up to 100 mV/g should be used. In no caseshould the peak g level exceed the acceleration range ofthe sensor. Be aware that signals generated by sensorresonance frequency can be 10 to 20 dB higher. Thiswould result in amplifier overload and signal distortion;therefore generating erroneous data.

Higher sensitivity accelerometers are available for specialapplications, such as low frequency/low amplitudemeasurements. In general, higher sensitivityaccelerometers have limited high frequency operatingranges. One of the excellent properties of thepiezoelectric sensor is its wide operating range. It isimportant that anticipated amplitudes of the applicationfall reasonably within the operating range of the sensor.Velocity sensors with sensitivities ranging from 20 mV/in/sec to 500 mV/in/sec (0.8 mV/mm/sec to 20 mV/mm/sec) are available. For most applications, a sensitivity of100 mV/in/sec (4 mV/mm/sec) is satisfactory.

THE FREQUENCY RANGE

The high frequency range of the sensor is constrained byits increase in sensitivity as it approaches resonance. Thelow frequency range is constrained by the amplifier roll-off filter, as shown in Figure 3. Many sensors have apassive low pass filter between sensor element and theamplifier in order to attenuate the resonance amplitude.

This extends the operating range and reduces electronicdistortion. The user should determine the high frequencyrequirement of the application and choose a sensor withan adequate frequency range while also meetingsensitivity and amplitude range requirements.

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Vibration Sensors Introduction / Selection 5

Figure 3. Powering scheme.

Monitor

18 to 30 VDC

+

+500k

22 µF( 35 VDC)

2–10 mACCD

Connector

Shield

Isolation Layer

Crystal

Amplifier

Preferred Twisted

Pair

Shield Connected To Sensor Housing

SafetyGround

HIGH AMPLITUDE VIBRATION SIGNALS

The sensor operating environment must be evaluated toensure that the sensor’s signal range not only covers thevibration amplitude of interest, but also the highestvibration levels present at the measurement point.Exceeding the sensor’s amplitude range will cause signaldistortion throughout the entire operating frequency rangeof the sensor. In other words, mechanical shock loadingon the sensor or large degrees of machine movement canoverload the sensor’s response capability. Shaker screensused in materials processing are an example of such anapplication.

The machine can generate high impacts compared to the"normal" working level, but an impact, a step, also causesexcitation of the sensor resonance frequencies. The gainis then 10 to 20 dB higher.

HAZARDOUS ENVIRONMENTS: GAS, DUST, ETC.

Vibration sensors must be agency certified for use inareas subjected to hazardous concentrations of flammablegas, vapor, mist, or combustible dust in suspension.Intrinsic Safety requirements for electrical equipmentlimit rapid electrical and thermal energy to levels that areinsufficient to ignite an explosive atmosphere undernormal or abnormal conditions. Even if the fuel-to-airmixture in a hazardous environment is in its most volatileconcentration, certified vibration sensors properlyinstalled are incapable of causing ignition. This greatlyreduces the risk of explosions in environments wherevibration sensors are needed. Many industrial vibrationsensors are now certified for Intrinsically-Safeinstallations by certifying agencies, such as FactoryMutual (FM), Canadian Standards Association (CSA),and CENELEC approved agencies.

For approval to CENELEC standards, SKF uses theElectrical Equipment Certification Service (EECS)(BASEEFA) of the United Kingdom.

Most certifying agencies also require the use of approvedsafety barriers when a monitoring system is installed in anonhazardous environment. Safety barriers ensure thatthe electrical energy passing from the nonhazardouslocation to the hazardous location does not exceed a safevalue. In general, such devices may also reduce the signalamplitude of a sensor.

Please consult SKF for more information on IntrinsicSafety.

In applications such where extremeconcentration of caustic chemicals arepresent that could denigrate the sensorcable and/or connector it may be advisableto use integral polyurethane or teflon cablesor purged sensor housings. Please consultSKF for more information when suchconditions exist.

CE MARK

Beginning January 1996, the EuropeanCommunity requires equipment sold in Figure 4. Range of linear operation.

2V Below Supply Voltage

Bias Output Voltage

2V Above Ground

Peak AmplitudeRange

Supply Voltage

Ground

~~

~~

their area to be a CE marked product. Because sensorshave an active component such as the integrated circuitamplifier, the sensor should have the CE mark.

Electrical Powering RequirementsMost internally amplified vibration sensors require aconstant current DC power source. Generally, the powersupply contains an 18 to 30 Volt source with a 2 to 10 mAconstant current diode (CCD) shown in Figure 3 . Whenother powering schemes are used, consultation with thesensor manufacturer is recommended. A more thoroughdiscussion of powering requirements follows.

AC COUPLING AND THE DC BIAS VOLTAGE

The sensor output is an AC signal proportional to thevibration of the structure at the mounting point of thesensor. The AC signal is superimposed on a DC biasvoltage (also referred to as Bias Output Voltage or RestVoltage). The DC component of the signal is blocked bya capacitor. The capacitor, however, passes the ACoutput signal to the monitor. SKF monitors and sensorpower supply units contain an internal blocking capacitorfor AC coupling. If not included, a blocking capacitor

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6 Vibration Sensors Introduction / Selection

Figure 5. Mounting techniques.

must be field installed. The combination ACcoupling capacitance and input defines the lowfrequency response of the system.

AMPLITUDE RANGE AND THE SUPPLYVOLTAGE

The sensor manufacturer usually sets the biasvoltage halfway between the lower and uppercutoff voltages (typically 2V above groundand 2V below the minimum supply voltage).The difference between the bias and cutoffvoltages determines the voltage swingavailable at the output of the sensor. Theoutput voltage swing determines the peakvibration amplitude range. (See Figure 4.)Thus, an accelerometer with a sensitivity of100 mV/g and a peak output swing of 5 voltshas an amplitude range of 50 g peak.

– NOTE –

If a higher supply voltage is used (22 to 30 VDC), theamplitude range can be extended to 100 g peak. If a voltagesource lower than 18 volts is used, the amplitude range will

be lowered accordingly.

CONSTANT CURRENT DIODES

Constant current diodes (CCD) are required for two wireinternally amplified sensors. In most cases, they areincluded in the companion power supply unit or monitorsupplied. Generally, battery powered supplies contain a 2mA CCD to ensure long battery life. Line poweredsupplies (where power consumption is not a concern)should contain 6 to 10 mA CCDs when driving longcables. For operation above +212°F (+100°C), whereamplifier heat dissipation is a factor, the current should belimited to less than 6 mA.

If the power supply does not contain a CCD for sensorpowering, one should be placed in series with the voltageoutput of the supply.

– NOTE –

Ensure that proper diode polarity is observed! Typical CCDs are Motorolaand Siliconix (4 mA part number 1N5312 and J510 respectively).

Other Sensor TypesHIGH TEMPERATURE PIEZOELECTRICVIBRATION SENSORS

High temperature industrial sensors are available forapplications up to +707°F (+375°C). Currently, hightemperature sensors are not internally amplified above+302°F (+150°C). Above this temperature, piezoelectricsensors are unamplified (charge mode). Charge modesensors usually require a charge amplifier. The sensitivityof unamplified sensors should be chosen to match theamplitude range of the amplifier selected. The unit ofsensitivity for charge mode accelerometers is expressed inpico coulombs/g. It is necessary to use special low-noise,high temperature cables to avoid picking up erroneoussignals caused by cable motion.

The electromagnetic (Inductive) velocity sensorsavailable from SKF are rated to maximum operatingtemperatures of +707°F (+375°C). Research is underwayto extend the operating temperature of amplifiedtransducers.

HAND-HELD AND OTHER MOUNTING METHODSFOR INDUSTRIAL SENSORS

Hand-held accelerometers such as the CMSS 92C arepopular sensors to do quick and easy data collections.These sensor types however have some disadvantages.The frequency range is limited to approximately 1,000Hz, thus they are generally okay only for low frequencyacceleration and velocity measurements. The contactresonance frequency is low at around 1,000 – 2,000 Hz.

The two-pole curved surface magnet with the two linewedges gives a slightly better frequency response andtherefore the contact resonance frequency is slightlyhigher. It is recommended that neither type be used forAcceleration Enveloping (ACC ENV) measurement inband III and band IV. The flat magnet mounted on aprepared flat measuring surface or methods 4, 5 and 6(Figure 5 Mounting Techniques) gives an excellentmounting method to provide reliable results for allmeasuring techniques.

Care should be taken to allow for the resonances inherentwith all mounting methods. Because protable datacollectors are highly versatile instruments, capable ofexecuting various measuring techniques, including highfrequencies, the choice should be the flat magnetmounting techniques and up. Methods 1 and 2 can beused for velocity measurements and low frequencyacceleration.

6

Stud

5

Adhesive

3

FlatMagnet

2

2-PoleMagnet

1

Probe Tip

4

AdhesiveMounting Pad

1

23

4 5 6

Rel

ativ

e S

ensi

tivi

ty (

dB

)

Frequency (Hz)

1 10 1,000 10,000 100,000

–10

0

10

20

30

–20100

Page 10: 268580

CMSS 786M Dual Sensor 7

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

+20

+10

0

-10

-20

Dev

iati

on

, %S

ensi

tivi

ty

Temperature, °F (°C)

TYPICAL TEMPERATURE RESPONSEFOR ACCELEROMETER AND SEE SENSOR

0.5 10 100 1 k 10

30

10

0

–10

–30

20

–20

Frequency, Hz

Dev

iati

on

, dB

TYPICAL FREQUENCY RESPONSEFOR ACCELEROMETER

Features• Measures acceleration and SEE

units

• Electronic resonance damping

• Miswiring protection

• One second current settling time

• Low sensitivity to thermalgradients and base strain

SpecificationsACCELEROMETER

DYNAMIC

Sensitivity: ± 10% of 100 mV/g; at +77°F (+25°C)Acceleration Range: 80 g peakAmplitude Nonlinearity: 1%Frequency Response: ± 10%; 1.0–9,000 Hz, ± 20%; 0.5–14,000 HzResonance Frequency, Mounted, Nominal: 22 kHzTransverse Sensitivity, Maximum: 5% of axialBase Strain Sensitivity, Maximum: 0.0002 g/µstrainElectromagnetic Sensitivity, equivalent g: 70 µg/GaussTemperature Response: See graph

SEE™ Sensor

DYNAMIC

Sensitivity: 100 kHz to 500 kHzNominal: 10 mV/SEE ± 2 dBSensor Capacitance, Nominal: 500 pFGrounding: Case isolatedCoupling Capacitance to Case: < 25 pF

ELECTRICAL

Power Requirement:Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1, 2): 2–10 mA

Electrical Noise: 2 Hz; 20 µg/√HzOutput Impedance, Maximum: 100 ΩBias Output Voltage, Nominal: 12 VDCGrounding: Case isolated, internally shielded

CMSS 786M Dual Sensor-Accelerometer and SEE™ Sensor,Piezoelectric

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 500 g peakShock Limit, Minimum: 5,000 g peakSealing: Hermetic

PHYSICAL

Weight: 95 gramsCase Material: 316L Stainless SteelMounting: 1/4-28 UNF Tapped HoleMounting Torque: 24 in-lbs (2,9 N-m)Output Connector: Amphenol PC1H-10-98PConnections: Pin A Case

Pin B SEE Sensor (–)Pin C SEE Sensor (+)Pin D Accelerometer, CommonPin E Accelerometer, Power and Signal

Cabling:Mating Connector (6-Pin): PC06-10-98S (Meets requirements of

MIL-C-26482)Recommended Cable: J9T2PS, Two shielded conductor pairs,

clear teflon jacket (100Ω nominal).

Accessories Supplied1/4-28 Mounting Stud, Calibration Data.

Accessories AvailableMetric Thread Mounting Studs, Splash-proof Cable Assembly, MagneticMounting Bases, Cementing Studs.

0.75"(19mm)

Diameter

7/8" HEX

2.00"(50mm)

6-PinConnector

1/4-28MountingHole

+4 +32 +77 +122 +176 +248(-20) (0) (+25) (+50) (+80) (+120)

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8 CMSS 793T-3 Accelerometer

CMSS 793T-3 Multifunction Sensor: Acceleration and Temperature

Features

• Measures both temperature andacceleration

• Rugged construction• Hermetically sealed• Ground isolated• ESD protection• Miswiring protection

SpecificationsDYNAMIC

Sensitivity: ± 5% of 100 mV/g; at +77°F (+25°C)Electrical Noise: 2 Hz; 40 µg/√HzPeak Amplitude (+24V supply): 80 gFrequency Response: ± 5%; 1.5–5,000 Hz

± 10%; 1.0–7,000 Hz± 3 dB; 0.5–15,000 Hz

Resonance Frequency, Mounted, Nominal: 24 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graphTemperature Sensor:

Temperature Output Sensitivity: ± 5% of 10 m Vdc/KelvinTemperature Measurement Range: -58°F to +248°F (+223°K to

+393°K)

NOTE: Each channel (acceleration and temperature) requires standard current powering for use with multiplexed sensors and data collector voltageinputs. Common leads are connected together inside the sensor.

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+10

0

-10

-20

Temperature, °F (°C)

0.5 10 100 1 k 20 k

3

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0

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2

–2

Frequency, Hz

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ACCELEROMETERTYPICAL TEMPERATURE RESPONSE TYPICAL FREQUENCY RESPONSE

ELECTRICAL

Power Requirement: Voltage Source: 18–30 VDCCurrent Regulating Diode: 2–10 mA

Bias Output Voltage, Nominal: 12 VDCTurn-On Time: 3 secondsShielding: Isolated Faraday

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 500 g peakShock Limit: 5,000 g peakElectromagnetic Sensitivity, equivqlent g: 10 µg/GaussSealing: HermeticBase Strain Sensitivity, Maximum: 0.0005 g/µstrain

PHYSICAL

Weight: 115 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF tapped holeMounting Torque: 24 in-lbs (2,9 N-m)Output Connector: 3-Pin, MIL-C-5015Cabling: Mating Connector: Amphenol 97-3106A-10SL-4S

Recommended Cable: Three conductor shielded, Teflonjacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Mounting Stud, Calibration Data.

Accessories AvailableMetric Thread Mounting Studs, Splash-proof Cable Assembly, MagneticMounting Bases, Cementing Studs.

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Piezofet Amplifier

AA

AAAA

AAAA

LM35CZ

A

AA

AA

AACX

Pin APower andAccelerometerSignal

Pin CTemperatureSensorOutput/Power

Pin BAccelerometerReturn,TemperatureCommon

CMSS 793T Block Diagram

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

1.00"(25mm)

Diameter

15/16" HEX

2.42"(61mm)

3-PinConnector

1.78"(45mm)

1/4-28Mounting Hole

Wiring Scheme

Connector CablePin Function Conductor Color

Shell Ground Shield

A Accelerometer Power and Signal Red

B Accelerometer Return, Temperature BlackCommon

C Temperature Sensor Signal and Power White

Page 12: 268580

CMSS 797T-1 Accelerometer 9

CMSS 797T-1 Low Profile, Industrial IsoRing® Accelerometerwith Internal Temperature Sensor

Features

• Measures both temperature andacceleration

• Rugged general purpose• Corrosion resistant• Hermetically sealed• Ground isolated• ESD protection• Miswiring protection

SpecificationsDYNAMIC

Sensitivity: ± 5% of 100 mV/g; at +77°F (+25°C)Acceleration Range: 80 g peakAmplitude Nonlinearity: 1%Frequency Response, Nominal: ± 5%; 3.0–5,000 Hz

± 10%; 2.0–7,000 Hz± 3 dB; 1.0–12,000 Hz

Resonance Frequency: 26 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graph

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

+20

+10

0

-10

-20

Temperature, °F (°C)

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TYPICAL TEMPERATURE RESPONSE

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, dB

20 k10 100 1 k

3

1

0

–1

–3

2

–2

1

TYPICAL FREQUENCY RESPONSE

Frequency, Hz

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Piezofet Amplifier

AA

AAAA

AAAA

LM35CZ

A

AA

AA

AACX

Pin APower andAccelerometerSignal

Pin CTemperatureSensorOutput/Power

Pin BAccelerometerReturn,TemperatureCommon

CMSS 797T Block Diagram

2-Pin Connector

MIL-C-5015

1.05"(26mm)

Diameter

2.15"(54mm)

1/4-28Mounting

Thread

1.20"(30mm)

1.70"(43mm)

0.25" (6mm)

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

Wiring Scheme

Connector CablePin Function Conductor Color

Shell Ground via Sensor - - -

A Accelerometer Power and Signal Red

B Accelerometer Return, Temperature BlackCommon

C Temperature Sensor Signal and Power White

Temperature Sensor:Temperature Output Sensitivity: ± 5% of 10 m Vdc/KelvinTemperature Measurement Range: -58°F to +248°F (+223°K to

+393°K)

ELECTRICAL

Power Requirement: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1,2): 2–10 mA

Electrical Noise: 2 Hz; 15 µg/√HzOutput Impedance, Maximum: 100 ΩBias Output Voltage, Nominal: 12 VDCGrounding: Case isolated, internally

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 500 g peakShock Limit: 5,000 g peakElectromagnetic Sensitivity, equivalent g: 30 µg/GaussBase Strain Sensitivity, Maximum: 0.002 g/µstrain

PHYSICAL

Weight: 135 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF captive screwMounting Torque: 30 in-lbs (3,4 N-m)Output Connector: 3-Pin, MIL-C-5015Cabling: Mating Connector: Amphenol 97-3106A-10SL-3S

Recommended Cable: Three conductor shielded, Teflonjacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Captive Screw, Calibration Data.

Accessories AvailableM6 Captive Screw, Splash-proof Cable Assembly, Magnetic MountingBases, Cementing Studs.

Page 13: 268580

10 CMSS 376 Accelerometer

CMSS 376 High Temperature Accelerometer

Features

• Operates Up to +500°F(+260°C)

• Intrinsic safety certified option

• Charge output

• Hermetically sealed

• Ground isolated

• Industrial ruggedness

SpecificationsDYNAMIC

Sensitivity: +500°F (+25°C), nominal, 25 pC/gAmplitude Nonlinearity, to 250 g: 1%Frequency Response(note 1): ± 5%; 3.0–7,000 Hz

± 10%; 2.0–10,000 Hz± 3 dB; 1.0–13,000 Hz

Resonance Frequency: 32 kHzTransverse Sensitivity, Maximum: 7% of axialTemperature Response: See graph

ELECTRICAL

Capacitance, nominal(note 2): 500 pFResistance, minimum: 1,000 MΩGrounding: Case Isolated

ENVIRONMENTAL

Temperature Range: -58°F to +500°F (-50°C to +260°C)Vibration Limit: 500 g peakShock Limit: 5,000 g peakBase Strain Sensitivity, Maximum: 0.002 g/µstrainHumidity Limit: 100% relative

+20

+10

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-20

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TYPICAL TEMPERATURE RESPONSE TYPICAL FREQUENCY RESPONSE

Frequency, Hz

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Temperature, °F (°C)

PHYSICAL

Weight: 75 gramsCase Material: stainless steelMounting: 1/4-28 tapped holeMounting Torque: 24 in-lbs (2,9 N-m)Output Connector: 10-32 coaxialCabling: Mating Connector: R1 (Microdot 10-32)

Recommended Cable: J3, low noise, Teflon jacket, 30 pF/ft;100 pF/m

Accessories Supplied1/4-28 Mounting Stud, Calibration Data.

Accessories AvailableMagnetic Mounting Bases, Metric Thread Mounting Studs, CementingStuds, Cable Assemblies, Power Supplies.

10-32 Coaxial Connector

1/4–28Mounting

Hole

0.046" (1mm)SafetyWire Hole

7/8" HEX

0.85"(21mm)

Diameter

1.74"(44mm)

1.62"(41mm)

NOTES: 1. As measured through a CMSS 628 charge amplifier.2. Tested at output connector.

-58 -32 +122 +212 +302 +392 +500(50) (0) (+50) (+100) (+150) (+200) (+260)

Page 14: 268580

CMSS 793L Accelerometer 11

CMSS 793L Low Frequency Piezoelectric Accelerometer

Features

• High sensitivity• Ultra low-noise electronics for

clear signals at very low vibrationlevels

• Filtered to attenuate highfrequencies

• Hermetically sealed• ESD protection• Miswiring protection

Agency Approved ModelsCMSS 793L-CA Canadian Standards

CMSS 793L-FM Factory Mutual

SpecificationsDYNAMIC

Sensitivity: ± 5% of 500 mV/g; at +77°F (+25°C)Acceleration Range: 10 g peakAmplitude Nonlinearity: 1%Frequency Response, Nominal: ± 5%; 0.6–700 Hz

± 10%; 0.4–1,000 Hz± 3 dB; 0.2–2,300 Hz

Resonance Frequency, Mounted, Nominal: 15 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graph

ELECTRICAL

Power Requirements: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1, 2): 2–10 mA

Electrical Noise: 2 Hz; 1.8 µg/√HzOutput Impedance, Maximum: 100 ΩBias Output Voltage, Nominal: 10 VDCTurn-On Time: 7 seconds (BOV within 15% of nominal and

satisfactory for taking readings)Grounding: Case isolated, internally shielded

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+10

0

-10

-20

Temperature, °F (°C)

TYPICAL TEMPERATURE RESPONSE

3 k1 10 100 1 k

3

1

0

–1

–3

2

–2

TYPICAL FREQUENCY RESPONSE

0.2

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Frequency, Hz

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 250 g peakShock Limit: 2,500 g peakElectromagnetic Sensitivity, equivalent g: 20 µg/GaussSealing: HermeticBase Strain Sensitivity, Maximum: 0.0001 g/µstrain

PHYSICAL

Weight: 142 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF tapped holeMounting Torque: 24 in-lbs (2,9 N-m)Output Connector: 2-Pin, MIL-C-5015Connections: Pin A Signal/Power

Pin B CommonCabling: Mating Connector: Amphenol 97-3106A-10SL-4S

Recommended Cable: Two conductor shielded, Teflonjacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Mounting Stud, Calibration Data.

Accessories AvailableMetric Thread Mounting Studs, Splash-proof Cable Assembly, MagneticMounting Bases, Cementing Studs.

1.00"(25mm)

Diameter

15/16" HEX

2.42"(61mm)

2-PinConnector

1.78"(45mm)

1/4-28Mounting Hole

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

CSA

ApprovedFM

Page 15: 268580

12 CMSS 797L Accelerometer

CMSS 797L Low Profile, Low Frequency, Industrial IsoRing®

Piezoelectric Accelerometer

Features

• High sensitivity

• Ultra low-noise electronics forclear signals at very lowvibration levels

• Low frequency capable

• Filtered to eliminate highfrequencies

• ESD protection

• Miswiring protection

SpecificationsDYNAMIC

Sensitivity: ± 5% of 500 mV/g; at +77°F (+25°C)Acceleration Range: 10 g peakAmplitude Nonlinearity: 1%Frequency Response, Nominal: ± 5%; 0.6–850 Hz

± 10%; 0.4–1,500 Hz± 3 dB; 0.2–3,700 Hz

Resonance Frequency: 18 kHzTransverse Sensitivity, Maximum: 7% of axialTemperature Response: See graph

ELECTRICAL

Power Requirement: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1, 2): 2–10 mA

Electrical Noise: 2 Hz; 2 µg/√HzOutput Impedance, Maximum: 100 ΩBias Output Voltage, Nominal: 10 VDCTurn-On Time: 5 seconds (BOV within 15% of nominal and

satisfactory for taking readings)Grounding: Case isolated, internally shielded

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

+20

+10

0

-10

-20

Temperature, °F (°C)

Dev

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TYPICAL TEMPERATURE RESPONSE

0.2

TYPICAL FREQUENCY RESPONSE

1 10 100 1 k 4 k

3

1

0

–1

–3

2

–2

Frequency, Hz

Dev

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, dB

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 250 g peakShock Limit: 2,500 g peakElectromagnetic Sensitivity, equivalent g: 5 µg/GaussSealing: HermeticBase Strain Sensitivity, Maximum: 0.001 g/µstrain

PHYSICAL

Weight: 148 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF captive screwMounting Torque: 30 in-lbs (3,4 N-m)Output Connector: 2-Pin, MIL-C-5015Connections: Pin A Signal/Power

Pin B CommonCabling: Mating Connector: Amphenol 97-3106A-10SL-4S

Recommended Cable: Two conductor shielded, Teflonjacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Captive Screw, Calibration Data.

Accessories AvailableM6 Captive Screw, Splash-proof Cable Assembly, Magnetic MountingBases, Cementing Studs.

2-Pin Connector

MIL-C-5015

1.05"(26mm)

Diameter

2.15"(54mm)

1/4-28Mounting

Thread

1.20"(30mm)

1.70"(43mm)

0.25" (6mm)

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

Page 16: 268580

CMSS 732A Accelerometer 13

CMSS 732A High Frequency Accelerometer

Features

• Wide dynamic range

• Compact construction to fit intight spaces

• Wide frequency range

• Small size, lightweight

• Hermetically sealed

SpecificationsDYNAMIC

Sensitivity: ± 5% of 10 mV/g; at +77°F (+25°C)Acceleration Range(note 1): 500 g peakAmplitude Nonlinearity: 1%Frequency Response: ± 5%; 2.0–15,000 Hz

± 3 dB; 0.5–25,000 HzResonance Frequency, Mounted,Nominal: 60 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graph

ELECTRICAL

Power Requirement: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1, 2): 2–10 mA

Electrical Noise: 2 Hz; 126 µg/√HzOutput Impedance, Maximum: 100 ΩBias Output Voltage: 10 VDCGrounding: Case Grounded

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 500 g peakShock Limit: 5,000 g peakElectromagnetic Sensitivity, equivalent g: 100 µg/GaussBase Strain Sensitivity, Maximum: 0.005 g/µstrain

PHYSICAL

Weight: 13 gramsMaterial: 316L stainless steelMounting: 10/32 UNF tapped holeMounting Torque: 20 in-lbs (2,3 N-m)Output Connector: 10-32 coaxial (female)Cabling: Mating Connector: 10-32 coaxial

Recommended Cable: Coaxial, Teflon jacket, 30 pF/ft;100 pF/m

Accessories Supplied10-32 Mounting Stud, Calibration Data.

Accessories AvailableMetric Thread Mounting Studs, Cementing Studs, Magnetic MountingBases, Isolating Studs.

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

Dev

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+20

+10

0

-10

-20

Temperature, °F (°C)

TYPICAL TEMPERATURE RESPONSE

30 k10 100 1 k 10 k

3

1

0

–1

–3

2

–2

0.5

TYPICAL FREQUENCY RESPONSE

Dev

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, dB

Frequency, Hz

1/2" HEX

10-32CoaxialConnector

10-32 Mounting Hole

0.48"(12mm)

Diameter

0.93"(23mm)

0.49"(12mm)

Diameter

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

Page 17: 268580

14 CMSS 793V Transducer

CMSS 793V Piezoelectric Velocity Transducer

Features

• Industrial ruggedness

• Eliminates distortion caused byhigh frequency signals

• Corrosion-resistant

• Internally integrated to velocity

• Ultra low-noise electronics forclear signals at very low vibrationlevels

• Miswiring protection

Agency Approved ModelsCMSS 793V-EE EECS (BASEEFA)

CMSS 793V-CA Canadian Standards

CMSS 793V-FM Factory Mutual

SpecificationsDYNAMIC

Sensitivity: ± 10% of 100 mV/in/sec; at +77°F (+25°C)Velocity Range: 50 in/sec peakAmplitude Nonlinearity: 1%Frequency Response: ± 10%; 2.0–3,500 Hz

± 3 dB; 1.5–7,000 HzResonance Frequency, Mounted, Nominal: 15 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graph

ELECTRICAL

Power Requirement: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(notes 1, 2): 2–10 mA

Electrical Noise: 2 Hz; 100 µin/sec/√HzAbsolute Phase Shift, Nominal, the greater of: tan-1 2/f or 2°Output Impedance, Nominal 4 mA Supply, the greater of: 5,000/f or

200 Ω

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

+20

+10

0

-10

-20

Dev

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Temperature, °F (°C)

1 10 100 1 k 7 k

TYPICAL FREQUENCY RESPONSE

Frequency, Hz

TYPICAL TEMPERATURE RESPONSEFOR ACCELEROMETER

Bias Output Voltage, Nominal: 10 VDCGrounding: Case isolated, internally shielded

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 250 g peakShock Limit: 2,500 g peakElectromagnetic Sensitivity, equivalent in/sec: 25 µin/sec/GaussSealing: HermeticBase Strain Sensitivity, Maximum: 0.0005 in/sec/µstrain

PHYSICAL

Weight: 145 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF tapped holeMounting Torque: 24 in-lbs (2,9 N-m)Output Connector: 2-Pin, MIL-C-5015Connections: Pin A Signal/Power

Pin B CommonCabling: Mating Connector: Amphenol 97-3106A-10SL-4S

Recommended Cable: Two conductor shielded, Teflonjacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Mounting Stud, Calibration Data.

Accessories AvailableMetric Thread Mounting Studs, Splash-proof Cable Assembly,Magnetic Mounting Bases, Cementing Studs.

1.00"(25mm)

Diameter

15/16" HEX

2.42"(61mm)

2-PinConnector

1.78"(45mm)

1/4-28Mounting Hole

3

2

1

0

-1

-2

-3

Dev

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-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100 (+120)

EECS(BASEEFA) CSA

ApprovedFM

Page 18: 268580

CMSS 797V Accelerometer 15

CMSS 797V Industrial IsoRing® Velocity Accelerometer

Features

• Industrial ruggedness

• Eliminates distortion causedby high frequency signals

• Corrosion-resistant

• Internally integrated tovelocity

• Ultra low-noise electronics forclear signals at very lowvibration levels

• ESD protection

• Miswiring protection

SpecificationsDYNAMIC

Sensitivity: ± 10% of 100 mV/in/sec; at +77°F (+25°C)Velocity Range: 50 in/sec peak; 1,270 mm/sec peakAmplitude Nonlinearity: 1%Frequency Response:

± 10%; 2.0–3,500 Hz± 3 dB; 1.6–7,000 Hz

Resonance Frequency: 18 kHzTransverse Sensitivity, Maximum: 5% of axialTemperature Response: See graph

ELECTRICAL

Power Requirement: Voltage Source(note 1): 18–30 VDCCurrent Regulating Diode(note 1,2): 2–10 mA

Electrical Noise: 2 Hz; 100 µin/sec/√HzOutput Impedance, Nominal 4 mA Supply, the Greater of: 5,000/f or

200 ΩBias Output Voltage, Nominal: 10 VDCGrounding: Case isolated, internally shielded

ENVIRONMENTAL

Temperature Range: -58°F to +248°F (-50°C to +120°C)Vibration Limit: 250 g peakShock Limit: 2,500 g peakElectromagnetic Sensitivity, equivalent g: 50 µin/sec/GaussBase Strain Sensitivity: 0.004 in/sec/µstrainSealing: Hermetic

PHYSICAL

Weight: 148 gramsCase Material: 316L stainless steelMounting: 1/4-28 UNF captive screwMounting Torque: 30 in-lbs (3,4 N-m)Output Connector: 2-Pin, MIL-C-5015

Pin A Signal/PowerPin B Common

Cabling: Mating Connector: Amphenol 97-3106A-10SL-4SRecommended Cable: Two conductor shielded, Teflon

jacket, 30 pF/ft; 100 pF/m

Accessories Supplied1/4-28 Captive Screw, Calibration Data.

Accessories AvailableM6 Captive Screw, Splash-proof Cable Assembly, Magnetic MountingBases, Cementing Studs.

NOTES: 1. To minimize the possibility of signal distortion when driving long cables with high vibration signals, +24 to +30 VDC powering isrecommended. A higher level constant current source should be used when driving long cables (please consult the Manufacturer).

2. A maximum current of 6 mA is recommended for operating temperatures in excess of +212°F (+100°C).

+20

+10

0

-10

-20

Dev

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Temperature, °F (°C)

TYPICAL TEMPERATURE RESPONSE

Dev

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, dB

Frequency, Hz

TYPICAL FREQUENCY RESPONSE

7 k10 100 1 k

3

1

0

–1

–3

2

–2

1

2-Pin Connector

MIL-C-5015

1.05"(26mm)

Diameter

2.15"(54mm)

1/4-28Mounting

Thread

1.20"(30mm)

1.70"(43mm)

0.25" (6mm)

+32 +77 +122 +167 +212 +248(0) (+25) (+50) (+75) (+100) (+120)

Page 19: 268580

16 CMSS 85 Series Transducers

CMSS 85 Series High Temperature Inductive Velocity Transducer

CMSS 85-7 (+392°F/+200°C)

CMSS 85-8 (+392°F/+200°C)

CMSS 85-9 (+707°F/+375°C)

CMSS 85-10 (+707°F/+375°C)

Features

• Ideal for Gas Turbine Engines

• Zero Friction Coil

• OEM Standard

• Hermetically sealed

• Approval for Class I, Division 1,Groups A, B, C, D

Utilizing a zero friction coil suspension, these hightemperature velocity transducers provide accurate andrepeatable vibration measurements over a wide range ofamplitude and frequency. The transducers are constructedof thermally resistant materials which allow forcontinuous operation at temperatures up to +392°F(+200°C) or +707°F (+375°C) depending on the modelselected.

The coil bobbin is suspended by two non-twisting,circular “spider” springs that provide a clean frequencyresponse free of spurious resonances, from 15 Hz to 2,000Hz. The damping is electromagnetic and purely viscous.Friction prone air damping is not employed. Theacceleration threshold is virtually zero, thereby allowingthe detection of extremely small vibration at lowfrequencies.

The velocity transducers are available with an integral 10feet (3 meters) armored cable or with a 2-pin connector.

Separate cables, armored and unarmored are alsoavailable. The sealed stainless steel case and ruggedinternals ensure durability in the most hostileenvironments.

The sensitive axis of the transducer can be mounted inany direction.

SpecificationsAxis Orientation: AnySensitivity: 145 mV/in/sec (5.71 mV/mm/sec), ± 5%Sensitivity vs. Temperature: Less than 0.01%/°F (0.02%/°C)Cross Axis Sensitivity: Less than 10%Temperature Limits: See Temperature Range TableFrequency Range: 15 Hz to 2,000 HzDisplacement Limits: 0.07 inches pk-pk, (1.8mm) pk-pkAcceleration Limits: 0 to 50 g’sDamping (Electromagnetic): At +68°F (+20°C): 0.8

At +392°F (+200°C): 0.55At +707°F (+375°C): 0.4

Case to Coil Isolation: At +68°F (+20°C): 100 megohms minimumAt +392°F (+200°C): 10 megohms minimumAt +707°F (+375°C): 1.0 megohm minimum

Case Material: Stainless SteelSealing: HermeticWeight: 7.5 oz. (0.21 kg)

1.25"(31.7mm)

0.25"(0.63mm)

2.25" Maximum(57.1mm)

(+) Pin For Upward Motion

1.14" Maximum(28.9mm)

Temperature Range

Model Temperature CoilNumber Range Resistance Termination

CMSS 85-7 -65°F to +392°F 550 ohms 2-Pin Hermetic Sealed Connector(-54°C to +200°C)

CMSS 85-8 -65°F to +392°F 550 ohms Integral Cable, 10 feet (3 meters)(-54°C to +200°C)

CMSS 85-9 -65°F to +707°F 125 ohms 2-Pin Hermetic Sealed Connector(-54°C to +375°C)

CMSS 85-10 -65°F to +707°F 125 ohms Integral Cable, 10 feet (3 meters)(-54°C to +375°C)

Page 20: 268580

CMSS 85 Series Transducers 17

CMSS 85 Series High Temperature Inductive Velocity Transducer

CablesCMSS 4850-015: Armored 15 feet cable (4.6 meters) that

mates to CMSS 85-7 and CMSS 85-9 VelocityTransducers with the 2-pin connector.

CMSS 4850-015-593: Unarmored 15 feet (4.6 meters)cable with only 2 feet of the cable having armor atthe velocity transducer end of the cable. This cablemates to the CMSS 85-7 and CMSS 85-9 VelocityTransducers with the 2-pin connector.

CONNECTOR CONFIGURATION

Mating Connector/Cable Assembly Model 4850-XXXStandard Is Model 4850-015 (15 Feet)

2 Pin Hermetic Connector3/8-32 Thread

1.14"(28.9mm)

1.25"(31.7mm)

0.25"(0.63mm)

2.25" Maximum(57.1mm)

(+) Pin For

Upward Motion

FIXED CABLE CONFIGURATION

Shielded 2 Conductor (20 AWG) GlassInsulation, Inside Statinless Steel Armor

120 Inches(3 Meters)Or Specify

BOTTOM VIEW

0.15" (3.8mm)Diameter4 Holes On1.375" (35mm) B.C.

The 015 in the model number of the cables designates thecable length. If other cable lengths are desired specify thelength in feet, (i.e. 020, 025 etc.). It is preferred that cablelengths be ordered in increments of 5 feet (1.51 meter),(i.e. 015, 020, 025 etc.).

The termination of the cable end opposite that mating tothe velocity transducer is trimmed wire only.

The cable mating connectors are custom designed andproprietary assembled by the vendor and consequently arenot available for on-site cable fabrication.

RESPONSE LIMITS

15 100 1K 2K

Frequency (Hz)

Dev

iati

on

(d

B)

Page 21: 268580

18 CMSS 603A-1 and CMSS 603A-3 Power Supply Units

CMSS 603A-1 and CMSS 603A-3 Power Supply Units

Features

• CMSS 603A-1 has onechannel

• CMSS 603A-3 has threechannels

• Powers most CMSS 700Series accelerometers

• Battery powered

• Uses common 9 VDCbatteries

• Can drive up to 50 feet (15meters) of cable

SpecificationsINPUT CHARACTERISTICS

Voltage to Transducer: 27 VDCCurrent to Transducer: 2.4 mA DC, ± 20%Maximum Input Voltage: 10 V RMS

OUTPUT CHARACTERISTICS

Output Impedance (accelerometerattached to input): Same as transducerRecommended Load Impedance: >100 kΩ

TRANSFER CHARACTERISTICS

Frequency Response: Same as transducerChannels: CMSS 603A-1: 1

CMSS 603A-3: 3Channel Separation: CMSS 603A-1: Not applicable

CMSS 603A-3: >80 dB

BATTERY TEST CIRCUIT

LED Lights: >18 VDCBattery Life: CMSS 603A-1: >120 hours

CMSS 603A-3: >40 hours

POWER REQUIREMENTS

Batteries: Three (3) 9V alkaline

ENVIRONMENTAL

Temperature Range: +32°F to +131°F (0 to +55°C)

PHYSICAL CHARACTERISTICS

Size: 3.0" (W) x 2.4" (H) x 4.0" (D) [76mm (W) x 61mm (H) x 102mm(D)]

Weight: CMSS 603A-1: 340 gramsCMSS 603A-3: 380 grams

Connectors: Signal Input: BNCSignal Output: BNC

Accessories SuppliedThree (3) 9V alkaline batteries

Page 22: 268580

Vibration Sensor Installation 19

Vibration Sensor Installation Considerations

CABLING REQUIREMENTS

Cabling is one of the most important aspects of vibrationsensor installation. As with sensors and monitoringequipment, money saved by purchasing inferiorcomponents is usually a poor investment. Time and effortto troubleshoot problems related to poor cabling caneasily cost several times the cost of the original cable.Furthermore, measurement results can be unreliable andinaccurate, thereby defeating the purpose of the conditionmonitoring program in the first place. Careful attentionmust be given to six major considerations: cable type,cable length, routing, grounding, anchoring, andenvironment.

CABLE TYPE AND CHARACTERISTICS

The type of cable used in conjunction with either a hand-held sensor or a permanently mounted sensor is animportant factor in determining the quality of the signalsthat reach the vibration monitor. But typically theconsideration of cable type is more important forpermanently mounted sensors since the length of the cableis usually longer and, therefore, exposed to more possiblesources of noise.

In general, high quality cable is recommended and can bedefined as twisted pair, shielded cable. The sensor powerand signal are carried on individuals wires and the cable’sshield in grounded at either the sensor or the vibrationmonitor (see section on Cable Grounding).

For sensors with coaxial cable, the center conductorcarries the signal and power, while the outer braidprovides shielding and signal return. Normally, the cableshield is electrically isolated from the sensor housing.This isolates the shield from the mounting point of themachine and prevents ground loops. If a non-isolatedsensor is used, an isolated mounting pad should be used tobreak possible ground loops.

– NOTE –

In cases where the monitoring equipment uses an instrumentationamplifier and the sensor is not grounded at the monitor, coaxial cables arenot recommended since any type of noise will be picked up on the coaxial

cable’s shield and amplified along with the signal. It should beemphasized that coaxial cables are not recommended for use with

vibration monitors in an industrial environment. They are not ruggedenough and are susceptible to noise intrusion as discussed above.

CHARACTERISTIC IMPEDANCE

For monitoring vibration at higher frequencies or forapplications requiring a cable to carry a signal over a longdistance with minimum loss and distortion, thecharacteristic impedance is possibly the most importantcable parameter. The characteristic impedance, Zo is thecombined resistive and reactive components of the cable’sresistance to the flow of electrons. Its value depends onthe type of conductors, their size, spacing, whether (and

how tightly) they are twisted together and the type andamount of insulating material used.

If there is a substantial mismatch between thecharacteristic impedance of the transducer and the cable,or the cable and the monitoring system, an electricalreflection will occur at the point of the impedancemismatch. This electrical reflection will distort bothsignal strength and quality. Additionally, if there is a lackof control in the manufacture of the cable then Zo can varyover the length of the cable causing electrical reflections,distortion, and reduction in signal integrity within thecable itself.

For these reasons it is important to use high quality cablewhich is matched to both the transducer and themonitoring system. With SKF sensors and monitoringequipment, best results will be obtained with signal cablehaving a characteristic impedance of 120 ohms.

CABLE LENGTH AND CAPACITANCE

All cables have capacitance across their leads, thereforethe capacitance load on the output of the sensor increaseswith cable length. Generally, this capacitance is 30–45picofarads per feet (100–130 picofarads per meter),depending on the cable construction. After the cablelength has been determined, its effect on the sensoroperation should be evaluated. Capacitive loadingattenuates the high frequency output of accelerometers.

– NOTE –

Cable lengths for velocity transducers are less important since they areemployed at low frequencies and contain filtering of acceleration

components.

The use of high quality, twisted pair(s), shielded cable cangreatly improve the quality and reliability of vibrationmeasurements, together with permitting the use of longercable runs in the installation. For example, a twisted pair,shielded cable with < 20 pF/ft (< 60 pF/m) with 100 ohmsimpedance can be run for twice the distance of a standardcable with twice the capacitance.

AMPLITUDE RANGE VERSUS CABLECAPACITANCE

When the amplifier drives a long cable, its performance islimited by the current available from the Constant CurrentDiode (CCD) to charge the cable capacitance at highfrequencies. This limits the amount of voltage swingfrom the amplifier and may reduce the high frequencyamplitude range. The reduction of the amplitude rangeincreases the sensor’s susceptibility to high frequencyamplifier overload. This will cause signal distortion andproduce erroneous signals at low frequencies. Sources ofhigh frequency overload could be gear impacts or thebroadband hiss of a steam release valve. Most SKFsensors are protected from distortion caused by moderateoverloads.

Page 23: 268580

20 Vibration Sensor Installation

SUMMARY OF RECOMMENDED CABLECHARACTERISTICS

The recommended cable characteristics can besummarized as follows:

Type: Twisted pair(s), shielded

Capacitance across leads: < 20 picofarads/feet(60 pF/m)

Impedance: 120 ohms for signal cable

Wire gauge: 20–24 AWG (American Wire Gauge)

Shield type: Braided or foil

Insulation material: As required by operatingenvironment. Teflon has a higher temperaturetolerance. Tefzel is recommended where fireretardation properties and radiation resistant cablesare needed.

POWERING VERSUS CABLE LENGTH

Proper powering will reduce signal distortion in longcable applications. It is recommended that for cablelengths over 100 feet (30 meters), the constant currentsource should be 6 to 10 mA. In addition, the voltagesource should be no less than 24 V for maximumamplitude range. Even when using very short cables, thecurrent source should be increased if amplifier overloadsignals are present or suspected.

– NOTE –

For most industrial applications, cable lengths of 300-450 feet (100-150meters) are normally acceptable, as long as the sensor is not mounted on

a structure with high level vibrations.

– NOTE –

For European installations of Sensors and Local Monitoring Units (LMU's)the customer is referred to the CMMA 320 EMA Installation Manual

available from the SKF Zaltbommel, The Netherlands Office.

CABLE ROUTING AND ELECTROMAGNETICINTERFERENCE

Walkie-talkies, power lines, or even electrical sparks maycause signal interference. The following guidelines willeliminate many measurement errors due to electromagneticinterference and electrostatic discharge (ESD).

Assure that high quality, well shielded cables are used. Insuch environments 100% shield coverage is necessary. Ifcable splices are made, complete shielding continuity mustbe maintained.

Proper cable routing is imperative. Never run sensor cablealongside AC power lines; cables must cross AC power linesat right angles 3 feet (1 meter) away from the power line.Where possible, provide a separate grounded conduit toenclose the sensor cable. In addition, route the cable awayfrom radio transmission equipment, motors/generators,transformers and other high current charging conductor.

Finally, avoid routing the cable through areas prone toESD except in applications where it is unavoidable. For

Monitor

Internal ShieldIsolated From Housing

Figure 6. Ground loop from improper grounding.

Monitor

Ground Loop

Non-IsolatedAccelerometer

˜

Figure 7. Grounding at the Monitor.

example, in the area around a paper machine ESD can notbe escaped. Even though SKF sensors are protectedagainst ESD failure, temporary signals distortion mayappear at the monitor. Such signals usually appear as anoverload or a “ski-slope” shaped FFT.

CABLE GROUNDING AND GROUND LOOPS

The purpose of having one or more shields around a pairof signal lines is to reduce the coupling between theshielded signal line and other signal lines and to reducethe intrusion of external noise. Doing so protects thestrength and fidelity of the signal of interest.

Grounding of shields, and the way in which they aregrounded, has a dramatic effect on their effectiveness. Animproperly grounded shield may actually be worse thanno shield at all. In order to provide proper shielding andprevent ground loops, cable grounding should be carefullyconsidered. Ground loops are developed when a commonline (signal return/shield) is grounded at two points ofdiffering electrical potential. (See Figure 6.)

For sensors using two conductor/shielded cable, the signaland power are carried on one lead and the signal return onthe other. The cable shield serves to protect the signal

Page 24: 268580

Vibration Sensor Installation 21

Figure 10. Cable anchoring.

Figure 9. Dual isolated shield configuration.

from ESD and electromagnetic interference(EMI). The shield should be grounded at onlyone point, normally either to the monitor or tothe sensor housing. All SKF monitors aredesigned to accommodate grounding of thesensor cable shield at the monitor. (See Figure7). In cases where it is either impractical orimpossible to establish a ground at themonitor, it is acceptable to ground at thesensor–provided the sensor design allows forsuch a grounding scheme.

– NOTE –

Sensors mounted in Hazardous area’s and equipped with a

Zener barrier, may not be grounded at sensor side.

If the machine being monitored is wellgrounded and the transducer has a caseterminal, the shield can be connected there. Ifthe machine is not well grounded, or if there isno terminal available on the transducer, theshield should be connected to a good electricalground point at the machine. However, if ajunction box is used at the machine beingmonitored, it is acceptable practice to leave theshields open at the transducers and electricallyconnect all of the shields together in thejunction box. A ground wire should then berun from the “daisy chained” shields to a goodelectrical ground at the machine beingmonitored.

Some cables contain more than oneindividually shielded signal pair with theentire cable enclosed by an overall shield. Inthis case the recommended practice is toground the individual shields at the transducerand leave them open at the monitor. Theoverall shield should then be grounded at themonitor and left open at the transducers. If ajunction box is used, the overall shield must beelectrically continuous through the junctionbox and not connected to the other shields.

If, when grounding at the sensor, EMI signalsare found to affect the vibration signal, afiltering capacitor (0.01 µF, 200 V low loss)should be placed between the shield and thegrounded monitor. This capacitor prevents thepassage of low frequency ground currents, yetdiverts high frequency EMI signals to ground.(See Figure 8.)

Sources producing high levels ofelectromagnetic noise (such as radiotransmitters, static discharge, and motor busharcing) may require a cable with dual isolatedshields. In this configuration, the outer shieldis grounded to the sensor housing. The innershield, which is electrically isolated from theouter, is grounded to the monitor. The double

Figure 8. Multiconductor/shield configuration.

Monitor 0.01 µFHF Capacitor

(Optional)

AA

Attached to Machine Surface in Motion

MinimumClearance

1.45" (37mm)

AAAAAAAA

MinimumDistance

6.0" (150mm)

Cable Clamp

AMachine Surface

Splash-proof Connector

Splash-proof Connector

Fixed

0.01 µFHF Capacitor

(Optional)

Monitor

Internal ShieldIsolated From Housing

PREFERRED

Page 25: 268580

22 Vibration Sensor Mounting Requirements

shielding allows electrical chargesimpressed on the cable to be attenuatedtwice to minimize influence on thevibration signal. Similar to the previousconfiguration, it is recommended that acapacitor (0.01 µF, 200 V low loss) beplaced in the terminal box between theinner and outer shields to maximize thisprotection. (See Figure 9.)

– NOTE –

In all cases it is very important that the cable shieldbe properly grounded. Failure to do so in high EMI /

ESD environments can result in damage to the sensorelectronics.

CABLE ANCHORING

The cable should be anchored to reducestress at the cable terminations. Whensecuring the cable, leave just enough slackto allow free movement of theaccelerometer. Failure to leave enoughslack will cause undo stress on the cableand dramatically influence the sensorsoutput. (See Figure 10.)

Mounting RequirementsThe mounting configuration depends uponthe dynamic measurement requirementssuch as frequency and amplitude range.Other factors to be considered aremounting location, prohibitions,accessibility, and temperature. In general,there are four mounting configurations:threaded studs, adhesives, magnets andprobe tips (See Figure 11).

STUD MOUNTING

Threaded stud mounting results in thewidest frequency measurement range. Itis recommended for permanentmonitoring systems, high frequencytesting, and harsh environments.

The mounting point on the structureshould be faced 1.1 times greater than thediameter of the mounting surface of thesensor. For measurements involvingfrequencies above 1 kHz, the surface

should be flat within 0.001" (25 µm) and have surfacetexture no greater than 32 micro-inches (0.8 µm). Thetapped hole must be perpendicular to the mountingsurface and at least two threads deeper than the stud. Thiswill prevent a gap between the sensor and the mountingsurface, producing optimum frequency response.

Proper screw torque on the mounting stud is also required.Under-torquing the sensor reduces the stiffness of thecoupling. Over-torquing can cause permanent threaddamage to the sensor. See Figure 12 for recommendednominal mounting torques.

Figure 12. Stud mounting: surface preparation.

Figure 11. Mounting techniques.

6

Stud

5

Adhesive

3

FlatMagnet

2

2-PoleMagnet

1

ProbeTip

4

AdhesiveMounting

Pad

1

23

4 5 6

Rel

ativ

e S

ensi

tivi

ty (

dB

)

1 10 100 1,000 10,000 100,000

–10

0

10

20

30

–20

Stud Stud Size "A" Dimension "B" Dimension Torquein-lbs (N-m)

SF1 10-32 UNF 0.188" 0.250" 20(4.78mm) (6.35mm) (2,3)

CMSS30168700 1/4-28 UNF 0.250" 0.350" 24(6.35mm) (8.90mm) (2,9)

1/4-28 Captive Screw 0.250" 0.350" 30(6.35mm) (8.90mm) (3,4)

0.004"(100 µm)

A

0.001"(25 µm)

– A – "A""B"

> 1.1 × Sensor DiameterSurface Finish

32 µ in RMS(0.8 µm)

Before stud mounting the accelerometer, a coupling fluidshould be applied to the mating surfaces. The couplingfluid protects the mounting surface and optimizes thefrequency response by increasing the coupling stiffness.Suggested coupling fluids are machine oil or vacuumgrease. It is recommended that a thread adhesive such asLoctite 222 be used.

ADHESIVE MOUNTING

If a hole cannot be tapped properly into the machine, anadhesive mount is recommended. When using an

Page 26: 268580

Vibration Sensor Mounting Requirements 23

Table 2. Mounting adhesives.

tips may have structural resonances in the frequencyrange of interest, they should be made of steel and shouldnot exceed 6 inches (150mm) length.

Sensitivity ValidationSensitivity validation is not usually a requirement. Forexample, the procedure is unnecessary in applicationswhere gross vibrations are being measured and extremeaccuracy is not a concern. If high accuracy amplitudemeasurements are required, sensor calibration should beverified once a year and can normally be done on-site bya qualified technician with vibration generator/shakerdevice.

It is much better to regularly check or trend:

• Bias voltage of accelerometers with built inamplifier.

• Resistance of the inductive velocity meter.

SummaryVibration sensors are the initial source of machineryinformation upon which productivity, product quality andpersonnel safety decisions are based. It is crucial thatsensors be properly selected and installed to ensurereliable signal information. Procedures should beimplemented to monitor the performance of allmeasurement channels to further ensure the integrity ofthe vibration information base. Following this processwill increase the effectiveness of your vibrationmonitoring program and improve productivity of plantpersonnel and equipment.

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAdhesives Comments

Loctite Inc.: Number 325 Cyanoacrylate adhesive. Single component; sets up with 707 Activator quickly; use at temperatures below +200°F (+95°C) and

with low humidity. Surface must be clean and smooth. Remove by twisting the sensor.

Lord Chemical Products: Structural adhesive. Water resistant; useful to +250°FVersilok 406 (+120°C); cures to full properties at room temperature in

24 hours.

Hottinger Baldwin Structural adhesive with short curing time. Temperature Messtechnik: range: -328°F to +356°F (-200°C to +180°C). Surface Rapid Adhesive SX must be cleaned and roughened with medium coarse

emery paper (grade 18).

adhesive, the sensor may be directly attached to themachine or onto an adhesive mounting pad. Use of anadhesive mounting pad is recommended if repeatedremoval of the sensor is required.

– NOTE –

If the circuit grounding scheme requires the sensor case to be groundedto the machine, then the installer must ensure that the adhesive mountingpad is electrically grounded to the machine. If grounding at the adhesivemounting pad is not practical, a suitable option is to place a junction box

between the sensor and the monitor. The sensor shields can then bejumpered together and a common ground established at the machine.

The adhesive mounting pad is flat on one side with athreaded stud on the other. After the pad is adhered to themachine, the sensor is torqued onto the stud. A couplingfluid should be applied to the stud face that mates with thesensor.

In order to optimize the frequency response, machine thebonding surface flat within 0.001 inches (25 µm).Following standard adhesive bonding practice is criticalto durability. The surfaces should be abraded andcarefully cleaned with a solvent. Mixing and applicationof the adhesive must be in compliance with the adhesivemanufacturer. Suggested adhesives are shown in Table 2.

MAGNETIC MOUNTING AND PROBE TIPS

In walk around monitoring programs, magnet mounts andhand-held sensors may be used. The frequency range ofboth mounting methods is dramatically reduced whencompared to stud or adhesive mounts. Magnetic mountsare available with flat surfaces for flat locations or twopole configurations for curved surfaces. Because probe

Page 27: 268580

24 Vibration Sensor Mounting Accessories

Sensor Mounting Accessories

Mounting Hardware

Model CMSS 60139-4 Probe Tip(Stinger)

For hand-held use with sensors having 1/4-28UNF mounting hole.

Mounting: 1/4-28 UNF StudMaterial: Stainless SteelDimensions: 4.50" (114mm) stinger

Model CMSS 30168700 ThreadedMounting Stud (1/4-28 to 1/4-28)

Flanged sensor mounting stud, 1/4-28 threadon both sides.

Material: Stainless SteelRecommended Mounting Torque: 24 in-lbs (2,9 N-m)Frequency Response: Proper mounting on clean flat surface can

achieve the specified frequency response of sensor.

Model CMSS 30168701 Adaptor Stud (1/4-28 toM8)

Flanged sensor mounting stud, adapts 1/4-28 tappedthreads to M8 thread.

Material: Stainless SteelRecommended Mounting Torque: 24 in-lbs (2,9 N-m)Frequency Response: Proper mounting on clean flat surface can

achieve the specified frequency response of sensor.

Model CMSS 30168703 Adaptor Stud (1/4-28 toM6)

Flanged sensor mounting stud, adapts 1/4-28tapped threads to M6 thread.

Material: Stainless SteelRecommended Mounting Torque: 24 in-lbs (2,9 N-m)Frequency Response: Proper mounting on clean flat surface can

achieve the specified frequency response of sensor.

Model CMSS 30205300 Mounting Stud (1/4-28 to10-32)

Flanged sensor mounting stud, adapts 1/4-28 tappedthreads to 10-32 thread.

Material: Stainless SteelRecommended Mounting Torque: 20 in-lbs (2,3 N-m)Frequency Response: Proper mounting on clean flat surface can

achieve the specified frequency response of sensor.

Model CMSS 910M Cementing Stud with 1/4-28Male

Model CMSS 910F Cementing Stud with 1/4-28Female

Cementing studs for sensors with 1/4–28 tapped threadsto M6 threads. Includes key notch for consistent triaxialaxis orientation.

Material: Stainless SteelRecommended Mounting Torque: 24 in-lbs (2,9 N-m)Frequency Response: Flat up to about 80% of the specified response

value, using epoxy or similar cement, flat up to about 30% of thespecified response value using double sided tape.

– NOTE –

To avoid sensor damage, always remove the sensor from the cementingstud first, then remove the stud from surface by means of a wrench using

the flats provided..

Model CMSS 10876700 Captive Screw

Metric Thread Captive Screw M6 x 43mm for CMSS 787and CMSS 797 Series Accelerometers.

Magnetic Mounting HardwareModel CMSS 908-RE, Rare Earth, flat bottom magnetbase for general purpose measurements. CMSS 908-REfor use with mounting stud sensors.

Model CMSS 908-RE Rare Earth Magnetic BaseFlat Bottom

Material: Rare earth cobalt mounted in a stainless steel housing.Frequency Response: Flat up to about 20% of the specified frequency

response.Holding Power: Approximately 40 lbs of force.Mounting: 1/4-28 UNF holeDimensions: 0.95" (24.1mm) Height x 0.75" (19.0mm) Diameter

Page 28: 268580

Vibration Sensor Mounting Accessories 25

Magnetic Bases for Curved SurfacesModels CMSS 908-MD and CMSS 908-HD are designedin a 2-pole configuration for industrial vibrationmonitoring applications where flat surfaces are rarelyfound. Each magnet is supplied with a 1/4-28 mountingstud to allow compatibility with most SKF transducers.

– NOTE–

Two-pole magnet bases are recommended for low frequencymeasurements only and only for applications where other mounting

methods are not practical.

Model CMSS 908-MD Medium Duty MagneticBase

For use in moderate conditions.

Material: Alnico magnet material mounted in an aluminum housingwith steel poles.

Frequency Response: Flat up to about 10% of the specified frequencyresponse.

Holding Power: Approximately 30 lbs of force.Mounting: 1/4-28 UNF holeDimensions: 1.38" (35.0mm) Height x 1.50" (38.0mm) Diameter

Model CMSS 908-HD Heavy Duty Magnetic Base

For use under extreme conditions.

Material: Alnico magnet material mounted in an aluminum housingwith steel poles.

Frequency Response: Flat up to about 10% of the specified frequencyresponse.

Holding Power: Approximately 70 lbs of force.Mounting: 1/4-28 UNF holeDimensions: 1.800" (45.0mm) Height x 2.125" (64.0mm) Diameter

Quick Connect/Disconnect SensorMounting PadsMounting Pads allow vibration technicians using suchinstruments as the SKF Microlog on walkaround routes toquickly mount vibration sensors in less than one turn.This quick mount design results in a decrease in mountingtime as compared to the older style threaded studmounting pads.

Key Benefits• Decreased sensor mounting time by 90%.

• Eliminates wrist fatigue from repetitive twisting.

• Combines ease and speed of a magnet mount withthe accuracy and repeatability of a permanentmount.

• Ensures the repeatable, reliable vibration data of apermanently mounted sensor.

• Prevents cable twisting.

• Upgrades existing installations.

Features• Constructed of corrosion resistant 316 stainless

steel.

• Convenient cement mounting capability.

• Accepts all 1/4-28 compatible vibration sensors,including SKF's low profile models.

• Compatible with existing 1/4-28 stud mountinstallations.

• Easily removed to upgrade to permanent mountallowing the sensor to be directly attached to thesame measuring point.

Model CMSS 910QDP-1 Stud Mounting Pad

The CMSS 910QDP-1 Mounting Pad is stud mounted tothe measuring point or attached to an existing 1/4-28 stud.

Easy conversion to permanently mounted sensors.

Once the CMSS 910QDP-1 is mounted, conversion topermanently mounted sensors is quick and easy. Bysimply removing the pad and attaching a SKF vibrationsensor to the existing 1/4-28 stud, sensor location andvibration data history remains reliable.

Model CMSS 910QDP-2 Cement Mounting Pad

The CMSS 910QDP-2 Cement Mounting Pad is epoxiedto the measuring point.

Removable for upgrading to permanently mountedsensors.

When upgrading to permanently mounted sensors, thecement pad can easily be removed to allow a studmounted sensor to be installed in the location.

Model CMSS 910QDB-1 Sensor Base

The CMSS 910QDB-1attaches easily to 1/4-28compatible sensors. Inwalkaround datacollection, the sensor canbe attached in less thanone turn to any of theQuick Connect/Disconnect mountingpads. The CMSS910QDB-1 can remain onthe sensor or be removedand reattached to otherpopular SKF vibrationsensors.

Machine Surface

Stud

CMSS 910QDP-1Mounting Pad

CMSS 910QDB-1Sensor Base

Sensor With 1/4–28 Mounting Stud

Machine Surface

Epoxy

CMSS 910QDP-2Cementing Pad

Page 29: 268580

26 Vibration Sensor Mounting Accessories

CMSS 50042300 Case Mounted Transducer Housing

Introduction

The CMSS 50042300 Case Mounted Transducer Housingprovides physical and environmental protection for theCMSS 766, CMSS 786, and CMSS 793 Series SeismicSensors. Use in installations where the pickup can besubject to possible damage from adverse conditions. Thishousing meets API 670 standards when properly installed.

The mounting kit includes a dome cover, mounting basewith one (1) 3/4" conduit connection, neoprene gasket,mounting screws, washers, and one (1) 1/2" NPTreducing bushing.

– NOTE –

Seismic sensor must be ordered separately.

Installation

The housing is compatible with 1/2" and 3/4" flex, EMT,and rigid conduit.

1. Select or prepare flat surface for installation ofprotective housing at the sensor location.

– NOTE –

If machine housing is radiused, surface the mounting area flat to maintaina full 360 degree gasket seal in the radiused plane and install with a

minimum of two (2) mounting screws 180 degrees apart.

2. Drill center for 7/32" pilot hole 0.313" deep andspotface 1.0" surface to 0.030" deep to 63 RMS finishfor direct mounted sensor installation. Tap center ofspotfaced surface for 1/4-28 UNF threads.

– NOTE –

A 63 RMS finish cannot normally be achieved using portable power toolstypically requiring the machine housing to be removed and milled to the

proper specifications in a machine shop. An alternative is to install amounting pad with the proper finish such as Part Number 70005050.

1.65"(42mm) Neoprene

Gasket1.50"

(38mm)

3/4" NPT

2.50" (63.5mm)

3.38"(86mm)

4.75" (120mm)

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

AAAAAAAAAAAA

AAAAAA

AAAAA

AAAA

AAA

AAAA

AA

AAAA

1.25" (31.7mm) Diameter± 0.050" (± 1.27mm)

0.281" (7.13mm) Diameter, 4 PlacesEqually Spaced on 1.62" (41.5mm) Diameter ± 0.010" (± 0.25mm)

4

5

6

7

8

3. Drill and tap four (4) equally spaced 1/4-20 UNC-2Bby 0.375" (10.0mm) deep on a 1.62" (42.0mm)diameter bolt circle.

4. Place neoprene gasket in place.

5. Install housing base over gasket, orienting conduitoutlet as required for your installation. Secure housingbase with four (4) each 1/4-20 UNC cap screws andlockwashers (provided).

6. Screw transducer into the center mounting hole. Donot exceed manufacturer’s torque recommendations(23 NM).

7. Place O-ring on dome cover and screw dome coverinto housing base until finger tight.

8. Optional 3/4" to 1/2" conduit reducing bushings cannow be installed.

Page 30: 268580

Vibration Sensor Mounting Accessories 27

70003010 Mounting Kit for Seismic Transducers

IntroductionThe 70003010 Mounting Kit for Seismic Transducer incorporatesthe CMSS 50042300 case mounted housing with high domecover, neoprene gasket, mounting screws, washers and a 1/2"reducing bushing. It contains all parts necessary to install apermanent stud mounted or adhesive mounted CMSS 766, CMSS786 and CMSS 793 Series Seismic Sensor. A nylon spacercomplete with 1-3/4" long cap screws is included in the kit forinstallations using cables with the J9T2 Splash-proof connector.Use in installations where the pickup can be subject to possibledamage from adverse conditions. When properly installed this kitmeets API 670 standards for mounting protective housingsindependent of the transducer to prevent affecting the frequencyresponse.

The kit includes one (1) each:

• 2.5" Housing with 3/4" conduit hub• 2.5" Dome cover• 3/4" to 1/2" RE conduit fitting (reducing bushing)• Four (4) 1/4-20 UNC x 3/4" cap screws• Four (4) 1/4-20 UNC x 1-3/4" cap screws (used for

installing housing with 1" nylon spacer)• Permanent/adhesive mounting pad 1/4" thick x 1" OD with

1/4-28 UNF threaded ID• Permanent mounting stud 1/4-28 UNF x 3/4" hardened steel• 2.5" nylon spacer 1" thick

Optional Kit AccessoriesPart Number 70005010 Piloted End Mill 1" x 7/32" pilot for spot

facing machine surface to accommodate accelerometermounting pad.

Part Number 70005020 406/17 Acrylic Epoxy BiPaks forinstallation of adhesive mounting pads.

– NOTE –Use 1/4-28 UNF captive mounting stud supplied with the transducer.

Part Number 70005015 Permanent Mounted TransducerInstallation Kit including 1" piloted end mill, two (2) each7/32" drill bits, 1/4-28 UNF tap set (starter and bottom taps),and ten (10) each 1/4-28 UNF hardened Allen studs.

Part Number 70005015 Permanent Mounted TransducerInstallation Kit including 1" piloted end mill, two (2) each7/32" drill bits, 1/4-28 UNF tap set (starter and bottom taps),and ten (10) each 1/4-28 UNF hardened Allen studs.

– NOTE –Seismic sensor must be ordered separately.

InstallationThe housing is compatible with 1/2" and 3/4" flex, EMT, and rigidconduit.

1. Select or prepare flat surface for installation of protective housingat the sensor location.

– NOTE –If machine housing is radiused, surface the mounting area flat to maintain

a full 360 degree gasket seal in the radiused plane and install with aminimum of two (2) mounting screws 180 degrees apart.

2. Drill center for 7/32" pilot hole 0.313" deep and spotface 1.0"surface to 0.030" deep for installation of permanent mountingpad.

CMSS 50042300 Case MountedTransducer Housing

J9T2 Splash-proof Connector

CMSS 766, CMSS 786, CMSS 793 Piezoelectric Transducer

70003000 Standoff Kit

70005050 Mounting Pad (Adhesive or Stud Mounted)Machine

Housing

70005052 Stud

Neoprene Gaskets

CMSS 31188600

– NOTE –Use Part Number 70005010 Piloted End Mill or equivalent.

3. Tap center for 1/4-28 UNF threads and install 1/4-28 UNF x 3/4"permanent mounting stud. Stud must be installed maintaining aperpendicularity of ± 1 degree to ensure proper coupling of themounting pad to the housing.

– NOTE –If using the adhesive mounting approach, it is not necessary to tap

threads and install the permanent mounting stud. Sufficiently degreasethe spotfaced surface and mounting pad, apply a release agent, (i.e.silicon grease) to the pad ID threads and install using Part Number

70005020 acrylic epoxy adhesive or equivalent. Allow adequate setup timefor adhesive bond before installing the sensor (2 hours minimum curingtime required, 24 hours recommended dependent on temperature and

humidity).

4. Drill and tap four (4) equally spaced 1/4-20 UNC by 0.313" deepon a 1.62" diameter bolt circle for installation of housing.

5. Screw permanent mounting pad onto the permanent stud andtighten snugly.

Hint: Apply silicon grease (i.e. DOW 44 or equivalent) to thestud threads and underside of pad to enhance the couplingcharacteristics and improve corrosion resistance.

– NOTE –After installation, verify that the exposed threads are at least 3/16" and no

more than 7/32". This is to ensure the sensor face contacts the padsurface and prevents the possibility of bottoming out on the sensor

threads adversely affecting the response characteristics.

6. Install sensor onto pad using permanent mounting stud or captivestud (adhesive mount). Do not exceed manufacturer's torquerecommendations (23 NM).

7. Install housing base over neoprene gasket orienting conduit hubas required for your installation. Secure housing base with four(4) 1/4-20 UNC x 3/4" cap screws and lockwashers.

– NOTE –When using J9T2 type Splash-proof Cable Connectors install 1" nylon

spacer and neoprene gasket between the housing base and the machinemounting surface with four (4) 1/4-20 UNC x 1-3/4" cap screws and

lockwashers.

8. Place O-ring on dome cover, screw into housing base finger tightmaking sure sensor cable is not chafed or damaged in the process.

9. Attach conduit using RE reducing bushing if necessary.

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28 Vibration Sensor Housings

Vibration Sensor Housings

The Transducer Housing encloses a seismic transducer,protecting it from mechanical damage and shielding it andthe electrical connections from water spray and otherenvironmental hazards. The transducer mounts to the 1/4-28 UNF mounting hole provided on the top of themounting adapter (provided).

– NOTE –

The operating frequency response of an accelerometer may be affectedwhen mounted in this housing due to the change in mass configuration. It

is not recommended for higher speed or light case to rotor weightmachinery applications, (i.e. gearbox, gas turbines, etc.).

Ordering InformationCMSS 30266101

Transducer Housing, 3/4" NPT mounting

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Mounting Adapter

5.87"(149.1mm)

4.75"(120.7mm)

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Hazardous Area Information 29

Hazardous Area Information

Area GeneralInformationReview the HazardousLocation Informationsection to properlydefine the area in whichthe sensors andmonitoring systems areto be installed, thendetermine whichequipment will meet thespecified requirements.

Sensors may either beinstalled in a Class 1,Division 1 (Zone 0, 1) or a Division 2 (Zone 2) hazardousarea. However, for installation in these areas, the sensorsmust be approved by an appropriate agency.

SKF Condition Monitoring does have vibration sensorsystems approved for installation in these areas andspecific model numbers assigned to easily identify theseagency approved options.

It is strongly recommended that intrinsic safety barriers beused for the hazardous area installations as the means oflimiting the thermal and electrical energy to the sensorcomponents in Class 1, Division 1 (Zone 0, 1) andDivision 2 (Zone 2) hazardous areas. The agencyapproved intrinsic safe sensor components, and theintrinsic safety barriers provide for a very high level ofsafety, and aid in the prevention of fire and explosions inyour facility.

It is recommended in field installations, that housings beused to provide physical protection for the SKF ConditionMonitoring Vibration Sensors.

SKF does provide a series of standard housings which canbe used for these installations.

Agency ApprovalsSKF Condition Monitoring has obtained agency approvalsfrom the following:

British Approvals Service forElectrical Equipment inFlammable Atmospheres EECS (BASEEFA)

EECS (BASEEFA) certified equipment is intended foruse in Zone 0, 1 as intrinsically safe in accordance withCENELEC European harmonized Standards, [EN50, 014(1977) and EN50 020 (1977)] and is accepted by membercountries of Austria, Belgium, Denmark, Finland, France,Germany, Greece, Ireland, Italy, Luxembourg, theNetherlands, Norway, Portugal, Spain, Sweden,Switzerland, and the United Kingdom.

Canadian Standards Association – CSA

CSA certified equipment is intended for use in Class 1,Division 1, Groups A, B, C, D.

Table 3. Agency approvals.

Factory Mutual Research, USA – FM

FM certified equipment is intended for use inClass I, Division 1, Groups A, B, C, D, E, F, G.

FM certified equipment is intended for use in Class I, II,III, Division 1 and 2, Groups A, B, C, D, E, F, G asspecifically indicated in Table 3.

CE Approval

European Community Declaration of Conformity.

Manufacturer:

SKF Condition Monitoring4141 Ruffin RoadSan Diego, California USA

Product: SKF Sensors

SKF Condition Monitoring, Inc. of San Diego, CaliforniaUSA hereby declares, that the referenced product, towhich this declaration relates, is in conformity with theprovisions of:

Council Directive 89/336/EEC (3 May 1989), on theApproximation of the Laws of the Member StatesRelating to Electromagnetic Compatibility, asamended by:

Council Directive 92/31/EEC (28 April 1992);

Council Directive 93/68/EEC (22 July 1993).

The above-referenced product complies with thefollowing standards and/or normative documents:

EN 50081-2, Electromagnetic compatibility–Genericemission standard. Part 2: Industrial environment(August 1993).

EN 50082-2, Electromagnetic compatibility–Genericimmunity standard. Part 2: Industrial environment(March 1995).

To order Vibration Sensors with the various agencyapprovals please refer to Table 3 for determination ofthe appropriate and specific model number to meetinstallation requirements.

CMSS 793 Class I, II, III/Division 1/Group A, B, C, D, E, F, G Class 1/Group A, B, C, D EEx ia IIC T4Class I, II, III/Division 2/Group A, B, C, D, F, G

CMSS 793L Class I, II, III/Division 1/Group A, B, C, D, E, F, G Class 1/Group A, B, C, DClass I, II, III/Division 2/Group A, B, C, D, F, G

CMSS 793V Class I, II, III/Division 1/Group C, D, E, F, G Class 1/Group A, B, C, D EEx ia IIC T4Class I, II, III/Division 2/Group A, B, C, D, F, G

CMSS 797 EEx ia IIC T4

Agency Approved Sensors

EECSSensor FM CSA CENELEC

(BASSEEFA)Approved

Approved

Page 33: 268580

30 Technical Notes–Reprints

Technical Notes (Reprinted by permission from Wilcoxon Research)

Piezoelectric Materials for Vibration Sensors–The Technical Advantages of Piezoceramics Versus Quartz

Piezoelectric sensors are used extensively for monitoringstructural and machinery vibrations. Piezoceramic PZT andquartz are the most widely used sensing materials foraccelerometers and piezovelocity transducers.

Piezoceramics and QuartzQuartz occurs naturally in a crystalline form, however, thequartz used in sensor fabrication is artificially grown.Piezoceramic material is also produced in a laboratoryenvironment through a highly controlled process specificallydesigned for accelerometer applications.

Lead-Zirconate Titanate (PZT) is a tailored piezoceramic that iscapable of measuring much lower amplitude vibrations thanquartz. For this and other reasons, PZT has been carefullyselected as the best piezoelectric material for accelerometers bythe worlds leading sensor research companies. Speciallyformulated PZT provides stable performance and long termreliability for modern piezoceramic sensors.

Quartz is used by companies who historically manufacturedforce gauges and pressure sensors. The lower efficiency ofquartz works well in these applications because of the high forcelevels measured in typical pressure and force gauge applications.However, quartz is not recommended for low frequencyaccelerometer applications.

APPLICATIONS

Slow Speed MachinerySlow speed machinery such as paper machines and coolingtowers, require the higher charge output and broader frequencyrange of PZT based sensors. Manufacturers who traditionallyused quartz are now using PZT in many of their newaccelerometer designs to allow for a variety of low frequencymonitoring applications.

LOW FREQUENCY MEASUREMENTS

Very little machinery vibration, in terms of acceleration, isexcited at low frequencies. For example: When monitoring aroll at 60 cpm, 10 mils pp of shaft movement (0.03 ips) producesonly 0.0005 g of acceleration. These low amplitude levels canapproach the electronic noise floor of standard accelerometers.Furthermore, a standard 100 mV/g accelerometer presents only50 µV of output to the data collector and may introduceinstrument noise into the measurement.

Piezoceramics must be used for low frequency 500 mV/gaccelerometers and piezovelocity transducers due to its lownoise characteristics. PZT enables these higher output voltagesensors to overcome data collector noise and further decreasesystem noise for low level vibration measurements.

HIGH FREQUENCY MEASUREMENTS

When monitoring higher frequencies the difference betweenPZT and quartz is less important. In terms of acceleration, thegeneral velocity alarm level of 0.3 ips, is equivalent to 2.5 g at30,000 cpm (500 Hz). This excitation level is easily measuredby most amplifiers and data collectors. However, the resonancefrequency of a PZT accelerometer will be much higher than anequivalent charge output quartz sensor. This can extend thefrequency range and give more accurate high frequencyreadings.

Temperature Considerations

Temperature considerations are very important in manyindustrial applications. Although quartz crystal is known for itstemperature stability, once designed into an accelerometer itshares many of the same characteristics as piezoceramic sensors.

As temperature increases, the sensitivity of both types ofaccelerometers will change. The sensitivity of PZT and quartzaccelerometers exhibit 5 to 7% sensitivity shifts from roomtemperature to +250°F (+121°C) as shown in Figure 13. In veryhigh temperature environments, both materials are usedsuccessfully in applications exceeding +500°F (+260°C).

Thermal Transients

Thermal transient effects must be considered in someapplications such as low frequency monitoring. Transientchanges in temperature cause thermal expansion of the sensor’smetal housing. Sometimes mistaken for the “pyroelectric”effect, thermal expansion produces false signals related to thestrain sensitivity of the sensor.

Accelerometers, whether PZT and quartz, should be designedfor low mechanical strain sensitivity to minimize the effects ofthermal transients.

Stability

Recalibration is rarely required for either type of sensor fornormal industrial applications unless contractually required.Quartz is naturally stable and will not change unlessmechanically overstressed. Modern PZT sensors are heattreated to stabilize the poling process and eliminate changes dueto long term temperature and shock exposure. Properlydesigned and processed sensors of both types have been fieldproven for many years.

Conclusion

Both piezoceramics and quartz are excellent materials for use insensor design. Each material has a clear technical advantageover the other for different parameters. Quartz is the bettermaterial for measuring pressure and force due to the relativelyhigh forces involved. Piezoceramics are clearly the choice foraccelerometer applications due to the higher sensitivitiesrequired to monitor low level vibration. Piezoceramics coupledwith an internal micro amplifier are the materials of choice foradvanced accelerometers.

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Quartz

+20

+10

0

-10

-20

TYPICAL TEMPERATURE RESPONSE

-58 -13 +32 +77 +122 +167 +212 +248(-50) (-25) (0) (+25) (+50) (+75) (+100) (+120)

Temperature, ° F (°C)

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, %S

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Figure 13. Typical temperature response of PZT and Quartz.

Page 34: 268580

Technical Notes–Reprints 31

Sensors Solutions for Industrial Cooling Towers and ProcessCooler Fans

Cooling towers are a critical component in many powergeneration, chemical, and other process facilities.Catastrophic equipment failure can result in safetyhazards, lowered production, and expensive repairs.Vibration monitoring of cooling tower fans, gear boxes,shafts, and motors provides early warning of machinedegradation and impending disaster.

Changes in Cooling Tower Monitoring

In the past, vibration monitoring was a technicalchallenge due to the slow rotational speeds, variety ofsupport structures, and wet corrosive environments.Mechanical ball/spring vibration cutoff switches weretraditionally used to shut down machinery when vibrationlevels became excessive. These switches have provenunreliable and in many instances allowed extensivemachinery damage before motor power was disabled.Furthermore, switches did not allow for advance warningof problems. Walkaround data collection systems havealso been found ineffective at measuring fan and gearboxdegradation. Today, cooling towers use permanentlyinstalled sensors to effectively and safely preventcatastrophic cooling tower failure without unscheduleddowntime.

Advanced Sensor Solutions For EarlyWarning Monitoring

By measuring vibration on a regular schedule, problemscan be located and repaired before failure occurs. The

most common mechanical problems are:

• Bearing failure.

• Motor soft foot.

• Shaft imbalance from thermal blow.

• Shaft imbalance from corrosion build up.

• Gear lock up from misalignment.

• Blade breakage due to stress corrosion.

• Chlorine corrosion of support structures.

Two types of sensors are recommended for monitoringcooling towers. Multipurpose Models CMSS 793 andCMSS 797 Accelerometers for the motor end, and ModelsCMSS 793L and CMSS 797L Low FrequencyAccelerometers for monitoring the gearbox and fan.

The CMSS 793 and CMSS 797 IsoRing® sensors exhibitthe broad frequency range required to simultaneouslymeasure drive speed, bearing harmonics, and highfrequency detection (HFD).

The CMSS 793L and CMSS 797L provides a strong 500mV/g output to overcome data collector noise at the lowfrequency fan speeds.

Table 5 gives mounting locations and trend indication.Table 6 gives sensor specifications. Figure 14 shows atypical arrangement for vibration monitoring of a coolingtower fan.

The “Payoff” of Vibration Monitoring

Todays predictive maintenance vibration monitoringprograms have proven to be both cost effective andreliable. Users of vibration monitoring programs confirmthat early detection, accurate problem pinpointing, andscheduled downtimes significantly drops repair bills andincreases the return on investment.

Modern machinery health monitoring gives the reliableinformation needed to confidently plan inspections andequipment maintenance without unexpected failures orwasted time.

Table 5. Mounting locations.

Sensor

CMSS793 or CMSS797100 mV/g IndustrialAccelerometer

Location

Horizontal on motor outboard and inboard bearings

Axial on motor outboard bearing

Horizontal on gear box at mesh

Frequency/Order Trend Indication1x motor Shaft imbalance1x, 2x, 3x, motor Parallel misalignment, looseness2x line Stator problems, soft foothf harmonics Bearing wear, loosenessHFD noise Bearing fault progression

1x, 2x, motor Bent shaft

1x, 2x, 3x, motor Angular misalignment

hf harmonics Bearing wear, looseness

1x fan Imbalance2x, 3x, fan LoosenessBlade pass Blade Failure2x mesh Gear misalignment3x Gear WearMesh harmonics Gear fault progression

CMSS 793 or CMSS 797100 mV/g IndustrialAccelerometer

CMSS 793L or CMSS 797L500 mV/g Low FrequencyAccelerometer

Table 6. Sensor specifications.

Sensor Specifications CMSS 793/CMSS 797 CMSS 793L/CMSS 797L

Sensitivity (mV/g) 100 500

Frequency Response (± 3 dB)CPM 30 to 900,000 12 to 138,000Hz 0.5 to 15,000 0.2 to 2,300

Spectral Noise at 1 Hz (60 cpm)g/ Hz 0.000056 0.000004ips/ Hz 0.0034 0.00025mils/ Hz 0.55 0.039

Voltage Output For 0.03 ipsvibration at60 cpm (µV) 49 244

Vibration MeasurementPoints

Sensor Location For Permanent Installation (CMSS 797L)

Fan

Gear Drive

Drive ShaftMotor

Figure 14. Typical sensor placement.

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32 Technical Notes–Reprints

Accelerometers Measure Slow Speed Rollers and Detect HighFrequencies

Successful vibration monitoring of paper machinesdepends on quality sensors, field proven for reliability.Accelerometers used in paper mill applications mustsurvive harsh thermal, electrical and chemicalenvironments while performing demanding bearingmeasurements. Piezoceramic accelerometers are thesensor of choice for accurately measuring the broad rangeof frequencies and low amplitudes occurring in slowspeed roller bearing installations.

Accelerometers are specially designed to maximizesensitivity to low level vibrations. Their low electronicnoise floor is needed to measure the vibration signature ofheavy, slow turning rollers. In addition, their highfrequency range allows advanced early detectiontechniques such as high frequency detection (HFD) andenveloping.

The heart of a paper mill quality accelerometer is leadzirconate-titanante (PZT), the piezoceramic pickup insidethe sensor. The charge sensitivity of PZT is over twentytimes that of quartz. High charge sensitivity is the criticalfactor governing electronic noise and the fidelity of slowspeed measurements.

Many vibration technicians have experienced the “skislope” effect when analyzing spectrums. The “ski slope”effect is due to amplification of the low frequency noise.Integration from acceleration to velocity magnifies thiseffect to produce a steeper “ski slope”. In paper machinemonitoring, low frequency noise must be reduced.Piezoceramics accomplish this in two ways.

First, the high sensitivity piezoceramic pickup lowers thespectral amplifier noise. This increase the signal-to-noiseration and prevents the integration noise “ski slope” from

hiding running speed information such as misalignmentand imbalance. Spectral noise should always be reviewedbefore selecting sensors for low frequency vibrationmeasurements.

Secondly, for a given low frequency spectral noise,piezoceramic sensors exhibit a higher resonancefrequency. Leaks in carbon steam seals and gear mesh onnearby equipment can overload low resonance sensorsand cause signal distortion. When integrated, thedistortion can “swamp” the running speed and low orderbearing fault frequencies in noise.

In addition to improving low frequency measurements,the high resonance allows the sensor to be used foradvance monitoring techniques. HFD techniques trendhigh frequency noise to detect early bearing degradation.Higher detection frequencies result in earlier bearing faultidentification.

Newer enveloping techniques capture the very highfrequency spectrum, similar to an AM radio detector, thesignal is demodulated to extract the low frequencyrepetition rate of the bearing signature. Higher frequencyenvelope bands contain less unwanted vibrationinterference and produce cleaner measurements.

Sensors are the "eyes and ears" of the predictivemaintenance system. When millions of dollars may besaved through early fault detection, selection of reliablesensors becomes critical. In paper machine applications,piezoceramics not only provide greater signal fidelity, butcan adapt to revolving monitoring techniques andrequirements. Quality measurements begin with using theproper sensor for the job.

Page 36: 268580

Glossary 33

Glossary

– A –ACCELERATION. The time rate ofchange of velocity. Typical units are ft/sec/sec, meters/sec/sec, and G’s (1 G = 32.17ft/sec/sec = 9.81 m/sec/sec). Accelerationmeasurements are usually made withaccelerometers.

ACCELEROMETER. Sensor whoseoutput is directly proportional toacceleration. Most commonly usepiezoelectric crystals to produce output.

ACCURACY. The quality of freedom frommistake or error, that is, conformity to truth,a rule or a standard; the typical closenessof a measurement result to the true value;the specified amount of error permitted orpresent in a physical measurement orperformance setup.

ACOUSTIC SENSITIVITY. The parameterquantifying output signal picked up by amotion transducer when subjected toacoustic fields.

ALIASING. A phenomenon which canoccur whenever a signal is not sampled atgreater than, twice the maximum frequencycomponent, causes high frequency signalsto appear at low frequencies. Aliasing isavoided by filtering out signals greater than1/2 the sample rate.

ALIGNMENT. A condition whereby theaxes of machine components are eithercoincident, parallel or perpendicular,according to design requirements.

AMPLITUDE. The magnitude of dynamicmotion or vibration. Amplitude isexpressed in terms of peak-to-peak, zeroto-peak, or RMS. For pure sine wavesonly, these are related as follows:

RMS = 0.707 times zero-to-peak;

peak-to-peak = 2 times zero-to-peak.

ANALOG-TO-DIGITAL CONVERTER (A/D, ADC). A device, or subsystem, thatchanges real-world analog data (as fromtransducers, for example) to a formcompatible with digital (binary) processing.

ANALYSIS RANGE (ANALYSISBANDWIDTH). (See FREQUENCY

RANGE.)

ANTI-ALIASING FILTER. A low-pass filterdesigned to filter out frequencies higherthan 1/2 the sample rate in order to preventaliasing.

ANTI-FRICTION BEARING. (SeeROLLING ELEMENT BEARING.)

ASCII (AMERICAN STANDARD CODEFOR INFORMATION INTERCHANGE). Aseven-bit code capable of representingletters, numbers, punctuation marks, andcontrol codes in a form acceptable tomachines.

ASYMMETRICAL SUPPORT. Rotorsupport system that does not provideuniform restraint in all radial directions.This is typical for most heavy industrialmachinery where stiffness in one planemay be substantially different than stiffnessin the perpendicular plane. Occurs inbearings by design, or from preloads suchas gravity or misalignment.

ASYNCHRONOUS. Vibration componentsthat are not related to rotating speed (alsoreferred to as nonsynchronous).

ATTENUATION. The reduction of aquantity such as sensitivity: i.e. throughfiltering or cable loading.

ATTRIBUTE. An individual field of a SETrecord or of a POINT record, acharacteristic of a POINT.

AVERAGING. In a dynamic signalanalyzer, digitally averaging severalmeasurements to improve statisticalaccuracy or to reduce the level of randomasynchronous components. (See RMS.)

AXIAL. In the same direction as the shaftcenterline.

AXIAL POSITION. The average position,or change in position, of a rotor in the axialdirection with respect to some fixedreference position. Ideally the reference isa known position within the thrust bearingaxial clearance or float zone, and themeasurement is made with a displacementtransducer observing the thrust collar.

AXIS. The reference plane used in plottingroutines. The X-axis is the frequencyplane. The Y-axis is the amplitude plane.

– B –BACKGROUND NOISE. The total of allnoise when no signal is input into theamplifier. (See BROADBAND NOISE.)

BALANCE RESONANCE SPEED(s). Arotative speed that corresponds to a naturalresonance frequency.

BALANCED CONDITION. For rotatingmachinery, a condition where the shaftgeometric centerline coincides with themass centerline.

BALANCING. A procedure for adjustingthe radial mass distribution of a rotor sothat the mass centerline approaches therotor geometric centerline.

BALL PASS INNER RACE (BPFI). Thefrequency at which the rollers pass theinner race. Indicative of a fault (crack orspall) in the inner race.

BALL PASS OUTER RACE (BPFI). Thefrequency at which the rollers pass theouter race. Indicative of a fault (crack orspall) in the outer race.

BALL SPIN FREQUENCY (BSF). Thefrequency that a roller turns within thebearing. Indicative of a problem with anindividual roller.

BANDPASS FILTER. A filter with a singletransmission band extending from lower toupper cutoff frequencies. The width of theband is determined by the separation offrequencies at which amplitude isattenuated by 3 dB (0.707).

BAND-REJECT. Also known as band stopand notch; a band-reject filter attenuatessignal frequencies within a specified band,while passing out-of-band signalfrequencies; opposite to the bandpassfilter.

BANDWIDTH. The spacing betweenfrequencies at which a bandpass filterattenuates the signal by 3 dB. In ananalyzer, measurement bandwidth is equalto [(frequency span)/(number of filters) x(window factor)]. Window factors are: 1 foruniform, 1.5 for Hanning, and 3.63 for flattop.

BASE STRAIN SENSITIVITY. Theparameter quantifying the unwanted outputsignal picked up by a motion transducerwhen its mounting surface is subjected tomechanical strains.

CAMPBELL DIAGRAM. A mathematicallyconstructed diagram used to check forcoincidence of vibration sources (i.e. 1Ximbalance, 2X misalignment) with rotornatural resonances. The form of thediagram is a rectangular plot of resonantfrequency (Y-axis) versus excitationfrequency (X-axis). Also known as aninterference diagram.

CAPACITANCE. The ratio of the electriccharge stored to the voltage applied acrossconductive plates separated by a dielectricmaterial (C = q/V).

CARTESIAN FORMAT. A graphicalformat consisting of two (2) orthogonalaxes; typically, Y is the vertical axis and Xis the horizontal axis. This format is usedto graph the results of one variable as afunction of another, e.g., vibrationamplitude versus time (Trend), frequencyversus amplitude (Spectrum) and 1Xamplitude versus shaft rotative speed(Bodé).

CASCADE PLOT. (See SPECTRAL

MAP.)

CAVITATION. A condition which canoccur in liquid-handling machinery (e.g.centrifugal pumps) where system pressuredecrease in the suction line and pump inletlowers fluid pressure and vaporizationoccurs. The result is mixed flow which mayproduce vibration.

CENTER FREQUENCY. For a bandpassfilter, the center of the transmission band.

CENTERLINE POSITION. (See RADIAL

POSITION.)

CHANNEL. A transducer and theinstrumentation hardware and relatedsoftware required to display its outputsignal.

CHARGE AMPLIFIER. Amplifier used toconvert charge mode sensor outputimpedance from high to low, makingcalibration much less dependent on cablecapacitance (also, charge converter).

CHARGE MODE ACCELEROMETER.Any piezoelectric accelerometer that doesnot contain an internal amplifier andproduces a high impedance charge signal.

CHARGE SENSITIVITY. A measure of theamount of charge produced by a chargemode accelerometer per unit ofacceleration. Usually given in terms ofpicocoulombs per g of acceleration; written(pC/g). (See COULOMB, VOLTAGE

SENSITIVITY.)

CLIPPING. Clipping is the term applied tothe generally undesirable circumstance inwhich a signal excursion is limited in somesense by an amplifier, ADC, or other devicewhen its full scale range is reached.Clipping may be “hard” in which the signalexcursion is strictly limited at some voltage;or, it may be “soft” in which case theclipped signal continues to follow the inputat some reduced gain above a certainoutput value.

CLONE. The process of exactlyduplicating a SET or a POlNT.

CLOSE. A SET or POINT is consideredCLOSED if the members below it in itshierarchy are not visible. Use LEFTARROW to CLOSE a SET or POINT. ASET or POINT that is marked on its left bya hyphen symbol is CLOSED (not OPEN).Its members are not displayed (not visibleon screen). (Also, See OPEN.)

BASELINE SPECTRUM. A vibrationspectrum taken when a machine is in goodoperating condition; used as a referencefor monitoring and analysis.

BAUD RATE (BIT RATE). The rate in bitsper second at which information istransmitted over a serial data link.

BENDER BEAM ACCELEROMETER. Anaccelerometer design which stresses thepiezoelectric element by bending it. Thisdesign is used primarily for low frequency,high sensitivity applications. (SeeCOMPRESSION MODE

ACCELEROMETER, SHEAR MODE

ACCELEROMETER.)

BIAS OUTPUT VOLTAGE. abr. BOV.Syns. Bias Voltage, Rest Voltage. The DCvoltage at the output of an amplifier onwhich the AC motion signal issuperimposed.

BLADE PASSING FREQUENCY. Apotential vibration frequency on any bladedmachine (turbine, axial compressor, fan,etc.). It is represented by the number ofblades times shaft rotating frequency.

BLOCK SIZE. The number of samplesused in a DSA to compute the Fast FourierTransform. Also the number of samples ina DSA time display. Most DSAs use ablock size of 1024. Smaller block sizereduces resolution, larger block sizeincreases resolution.

BLOCKING CAPACITOR. A capacitorplaced in series with the input of a signalconditioning or measurement device whichblocks the DC Bias Voltage but passes theAC Signal.

BODÉ. Rectangular coordinate plot of 1Xcomponent amplitude and phase versusrunning speed.

BOW. A shaft condition such that thegeometric centerline of the shaft is notstraight.

BRINNELING (FALSE). Impressionsmade by bearing roiling elements on thebearing race; typically caused by externalvibration when the shaft is stationary.

BROADBAND NOISE. The total noise ofan electronic circuit within a specifiedfrequency bandwidth. (SeeBACKGROUND NOISE.)

BUFFER. 1) An isolating circuit used toavoid distortion of the input signal by thedriven circuit. Often employed in datatransmission when driving through longcables. 2) A temporary software storagearea where data resides between time oftransfer from external media and time ofprogram-initiated I/O operations.

– C –CAGE (RETAINER). A component ofrolling bearings which constrains therelative motion of the rolling elementscircumferentially around the bearing.

CALIBRATION. Comparison of theperformance of an item of test andmeasuring equipment with a certifiedreference standard.

CALIBRATION CURVE. A graphicalrepresentative of the measured transduceroutput or instrument readout as comparedto a known input signal.

CALIBRATOR. Verifies that theperformance of a device or instrument iswithin its specified limits.

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– C –COHERENCE. The ratio of coherentoutput power between channels in a dual-channel DSA. An effective means ofdetermining the similarity of vibration at two(2) locations, giving insight into thepossibility of cause and effect relationships.The real part of a complex function. Thecomponent which is in phase with the inputexcitation. In frequency domain analysis,the coincident terms are the cosine termsof the “Fourier transform.”

COHERENCE FUNCTION. Coherence isa frequency domain function generallycomputed to show the degree to which alinear, noise-free relationship existsbetween a system input and the output.Values vary between one and zero, withone being total coherence and zero beingno coherence between input and output.

COMPRESSION MODEACCELEROMETER. An accelerometerdesign which stresses the piezoelectricelement in the compressive direction: i.e.the electrode faces move toward and awayfrom each other. (See BENDER BEAM

ACCELEROMETER, SHEAR MODE

ACCELEROMETER.)

CONDITION MONITORING. Determine ofthe condition of a machine by interpretationof measurements taken either periodicallyor continuously indicating the condition ofthe machine.

CONSTANT BANDWIDTH FILTER. Abandpass filter whose bandwidth isindependent of center frequency. Thefilters simulated digitally in a DSA areconstant bandwidth.

CONSTANT PERCENTAGEBANDWIDTH. A bandpass filter whosebandwidth is a constant percentage ofcenter frequency. 1/3 octave filters,including those synthesized in DSAs, areconstant percentage bandwidth.

CONTINUOUS SPECTRUM. The type ofspectrum produced from non-periodic data.The spectrum is continuous in thefrequency domain (See LINE

SPECTRUM).

COULOMB. symbol C. The SI unit ofelectric charge. The amount of chargetransported by one volt of electricalpotential in one second of time. One (1)picocoulomb = 10-12 coulombs.

CPM. Cycles per minute.

CPS. Cycles per second. Also referred toas Hertz (Hz).

CREST FACTOR. Relation between peakvalue and RMS value (Peak divided byRMS.)

CRITERIA. A means of selecting desireditems from the database. Very helpful ingenerating reports or downloading to theMICROLOG. The types of selection criteriathat can be set are POINTS IN ALARM,ENABLED POINTS, and OVERDUEPOINTS that fit a selectable date range.

CRITICAL MACHINERY. Machines whichare critical to a major part of the plantprocess. These machines are usuallyunspared.

CRITICAL SPEED MAP. A rectangularplot of system natural frequency (Y-axis)versus bearing or support stiffness (X-axis).

CRITICAL SPEEDS. In general, anyrotating speed which is associated withhigh vibration amplitude. Often, the rotorspeeds which correspond to naturalfrequencies of the system.

DIFFERENTIATION. Representation interms of time rate of change. For example,differentiating velocity yields acceleration.In a DSA, differentiation is performed bymultiplication by jw, where w is frequencymultiplied by 2π. (Differentiation can alsobe used to convert displacement tovelocity.)

DIFFERENTIAL EXPANSION. Themeasurement of the axial position of therotor with respect to the machine casing atthe opposite end of the machine from thethrust bearing. Changes in axial rotorposition relative to the casing axialclearances are usually the result of thermalexpansion during start-up and shutdown.Often incorporated as a measuredparameter on a steam turbine.

DIGITAL FILTER. A filter which acts ondata after it has been sampled anddigitized. Often used in DSAs to provideanti-aliasing protection after internalresampling.

DIGITAL-TO-ANALOG CONVERSION.The process of producing a continuousanalog signal from discrete quantizedlevels. The result is a continuouswaveform designed to match as closely aspossible a previously sampled signal or asynthesized result. Usually followed by alow pass filter.

DISCRETE FOURIER TRANSFORM. Aprocedure for calculating discretefrequency components (filters or lines) fromsampled time data. Since the frequencydomain result is complex (i.e. real andimaginary components), the number ofpoints is equal to half the number ofsamples.

DISPLACEMENT. The change in distanceor position of an object relative to areference.

DISPLACEMENT SENSOR. A transducerwhose output is proportional to the distancebetween it and the measured object(usually the shaft).

DOWNLOAD. Transferring information tothe Microlog from the host computer.

DYNAMIC DATA. Data (steady state and/or transient) which contains that part of thetransducer signal representing the dynamic(e.g., vibration) characteristics of themeasured variable waveform. Typicaldynamic data presentations includetimebase, orbit, frequency-based spectrum,polar, Bodé, cascade, and waterfall.

DYNAMIC MOTION. Vibratory motion of arotor system caused by mechanisms thatare active only when the rotor is turning atspeeds above slow roll speed.

DYNAMIC RANGE. For spectrummeasurements, the difference, in dB,between the overload level and theminimum detectable signal level (above thenoise) within a measurement system. Theminimum detectable signal of a system isordinarily fixed by one or more of thefollowing: noise level; low level distortion;interference; or resolution level. Fortransfer function measurements, theexcitation, weighting and analysisapproaches taken can have a significanteffect on resulting dynamic range.

– E –ECCENTRICITY, MECHANICAL. Thevariation of the outer diameter of a shaftsurface when referenced to the truegeometric centerline of the shaft. Out-of-roundness.

CRYSTAL CAPACITANCE. The electricalcapacitance across the terminations of apiezoelectric crystal. Usually given in termsof picofarads; written (pF).

CROSS AXIS SENSITIVITY. A measure ofoff-axis response of velocity andacceleration transducers.

CROSS TALK. Interface or noise in atransducer signal or channel which has itsorigin in another transducer or channel.When using eddy probes, cross talk canoccur when the tips of two (or more) probesare too close together, resulting in theinteraction of electromagnetic fields. Theeffect is a noise component on each of thetransducers’ output signals.

CURRENT REGULATING DIODE. Asemiconductor device which limits andregulates electrical current independent ofvoltage.

CURVEFITTING. Curvefitting is theprocess whereby coefficients of an arbitraryfunction are computed such that theevaluated function approximates the valuesin a given data set. A mathematicalfunction, such as the minimum meansquared error, is used to judge thegoodness of fit.

CYCLE. One complete sequence of valuesof a periodic quantity.

– D –DAMPING. The quality of a mechanicalsystem that restrains the amplitude ofmotion with each successive cycle.Damping of shaft motion is provided by oilin bearings, seals, etc. The dampingprocess converts mechanical energy toother forms, usually heat.

DAMPING, CRITICAL. The smallestamount of damping required to return thesystem to its equilibrium position withoutoscillation.

DATABASE. A group of SETs, subSETs,and POINTs arranged in a hierarchy thatdefine a user’s facilities (i.e., buildings,areas, machine, data gathering locations).Also a top menu bar function in PRISM2.Allows add to, change, and delete of datain the database.

DECIBELS (dB). A logarithmicrepresentation of amplitude ratio, definedas 20 times the base ten logarithm of theratio of the measured amplitude to areference. DBV readings, for example, arereferenced to 1 volt RMS. dB amplitudescales are required to display the fulldynamic range of a DSA.

DEFECT BEARING FREQUENCY.Frequency generated as a result of a defectin a bearing.

DEGREES OF FREEDOM. A phrase usedin mechanical vibration to describe thecomplexity of the system. The number ofdegrees of freedom is the number ofindependent variables describing the stateof a vibrating system.

DELAY. In reference to filtering, refers tothe time lag between the filter input and theoutput. Delay shows up as a frequency-dependent phase shift between output andinput, and depends on the type andcomplexity of the filter.

EDDY CURRENT. Electrical current whichis generated (and dissipated) in aconductive material in the presence of anelectromagnetic field.

ELECTROMAGNETIC INTERFERENCE.abr.: EMI. The condition in which anelectromagnetic field produces anunwanted signal.

ELECTROMAGNETIC SENSITIVITY. Theparameter quantifying the unwanted outputsignal picked up by a motion transducerwhen subjected to electromagnetic fields.

ELECTROSTATIC DISCHARGE. abr.:ESD. A very high voltage discharge,sometimes accompanied by a spark,caused by static electrical charges acrossa dielectric material, such as air. This is aproblem especially to electronic equipment,in hot, dry environments and plants wherelarge rollers transport textiles or paper andbuild up very large amounts of charge.

ENGINEERING UNITS. In a DSA, refersto units that are calibrated by the user (e.g.in/sec, g’s).

ENVELOPING. Screening technique toenhance pure repetitive elements of asignal.

EXTERNAL SAMPLING. In a DSA refersto control of data sampling by a multipliedtachometer signal. Provides a stationarydisplay of vibration with changing speed.

– F –FAST FOURIER TRANSFORM (FFT). Acomputer (or microprocessor) procedurefor calculating discrete frequencycomponents from sampled time data. Aspecial case of the discrete Fouriertransform where the number of samples isconstrained to a power of 2.

FIELD. One data item of a record.Examples of fields are first name, middleinitial, last name, room number, machineID, etc.

FILTER. Electronic circuitry designed topass or reject a specific frequency band.

FLAT TOP WINDOW. DSA windowfunction which provides the best amplitudeaccuracy for measuring discrete frequencycomponents.

FLUID-FILM BEARING. A bearing whichsupports the shaft on a thin film of oil. Thefluid-film layer may be generated by journalrotation (hydrodynamic bearing), or byexternally applied pressure (hydrostaticbearing).

FOLDING FREQUENCY. Equal to one-half of the sampling frequency. This is thefrequency above which higher signalfrequencies are folded or aliased back intothe analysis band.

FORCED VIBRATION. The oscillation of asystem under the action of a forcingfunction. Typically forced vibration occursat the frequency of the exciting force.

FRAME. Discrete set of elements(numbers) representing a time or frequencydomain function. The numerical size of theelement set is called the frame, block, orrecord size and is generally a power of 2,such as 64, 128, 256, etc. The term, framelength or block length, is used to describethe length of the element set in seconds ormilliseconds and is equal to N D t where Nis the frame size and D t is the samplinginterval.

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– F –FREE RUNNING. A term used to describethe operation of an analyzer or processorwhich operates continuously at a fixed rate,not in synchronism with some externalreference event. Analyzers, processorsand computing systems are often thoughtto be operating in a triggered, blocksynchronous or free running mode ofoperation.

FREE VIBRATION. Vibration of amechanical system following an initialforce–typically at one or more naturalfrequencies.

FREQUENCY. The repetition rate of aperiodic event, usually expressed in cyclesper second (Hz), revolutions per minute(RPM), or multiples of rotational speed(orders). Orders are commonly referred toas 1X for rotational speed, 2X for twicerotational speed, etc.

FREQUENCY COMPONENT. Theamplitude, frequency and phasecharacteristics of a dynamic signal.

FREQUENCY DOMAIN. An FFT graph(amplitude versus frequency).

FREQUENCY RANGE. The frequencyrange (bandwidth) over which ameasurement is considered valid; (i.e.,within manufacturer’s specifications).Typical analyzers have selectable ranges.Usually refers to upper frequency limit ofanalysis, considering zero as the loweranalysis limit (See ZOOM ANALYSIS).

FREQUENCY RESPONSE. The amplitudeand phase response characteristics of asystem.

FREQUENCY RESPONSE FUNCTION.The transfer function of a linear systemexpressed in the frequency domain.Commonly defined as the ratio of theFourier transform of the system’s responseto the Fourier transform of the system’sexcitation function as magnitude and phaseor real and imaginary parts. Whereas thetransfer function of a linear system is, in astrict sense, defined as the ratio of theLaPlace transform of the system responseto the LaPlace transform of the LaPlacetransform of the system response to theLaPlace transform of the system input, thefrequency response function is moregenerally used.

FTF. Fundamental Train Frequency.

FUNDAMENTAL. The lowest frequencyperiodic component present in a complexspectrum. At least one complete period ofa signal must be present for it to qualify asthe “fundamental.”

FUNDAMENTAL TRAIN FREQUENCY(FTF). The frequency at which the cagethat contains the rollers rotates. Indicativeof a fault in the cage.

– G –g. A standard unit of acceleration equal toone earth’s gravity, at mean sea level. Theacceleration of free-fall. One g equals32.17 ft/s2 (FPS) or 9.807 m/s2 (MKS).

GAIN. The factor by which an outputsignal exceeds an input signal; theopposite of attenuation; usually expressedin dB.

GEAR MESH FREQUENCY. A potentialvibration frequency on any machine thatcontains gears; equal to the number ofteeth multiplied by the rotational frequencyof the gear.

GLOBAL BEARING DEFECT. Relativelylarge damage on a bearing element.

GROUND LOOP. Current flow betweentwo or more ground connections whereeach connection is at a slightly differentpotential due to the resistance of thecommon connection.

– H –HANNING WINDOW. DSA windowfunction that provides better frequencyresolution than the flat top window, but withreduced amplitude accuracy.

HARMONIC. Frequency component at afrequency that is an integer multiple of thefundamental frequency.

HEAVY SPOT. The angular location of theimbalance vector at a specific laterallocation on a shaft. The heavy spottypically does not change with rotationalspeed.

HERTZ (Hz). The unit of frequencyrepresented by cycles per second.

HFD. High Frequency Detection. Adynamic high frequency signal from anaccelerometer which includes theaccelerometer’s resonant frequency. Forassessing the condition of rolling elementball or roller bearings.

HIGH-PASS FILTER. A filter with atransmission band starting at a lower cutofffrequency and extending to (theoretically)infinite frequency.

HIGH SPOT. The angular location on theshaft directly under the vibration transducerat the point of closest proximity. The highspot can move with changes in shaftdynamics (e.g. from changes in speed).

– I –IEEE 488 BUS. An industry standard busthat defines a digital interface forprogrammable instrumentation; it uses abyte-serial, bit-parallel technique to handle8-bit-wide data words.

IMBALANCE. Unequal radial weightdistribution on a rotor system; a shaftcondition such that the mass and shaftgeometric centerlines do not coincide.

INFLUENCE COEFFICIENTS.Mathematical coefficients that describe theinfluence of system loading on systemdeflection.

IN-PHASE (DIRECT) MOTIONCOMPONENT. (In F) The Cartesian valueof the 1X vibration transducer angularlocation. This may be expressed as: IN F =A cos Q, where A is the peak to peakamplitude, and Q is the base angle of the1X peak to peak amplitude, and Q is thephase angle of the 1X vector.

INNER RACE. A generally cylindricalcomponent of rolling bearings which ispositioned between the shaft and therolling elements.

INTEGRATED CIRCUITPIEZOELECTRIC. The industry standardpowering scheme using a current limitedvoltage supply for powering internallyamplified accelerometers and PVTs.

INTEGRATION. A process producing aresult that, when differentiated, yields theoriginal quantity. Integration ofacceleration, for example, yields velocityintegration is performed in a DSA bydividing by jw, where w is frequencymultiplied by 2π. (Integration is also usedto convert velocity to displacement.)

IsoRing®. A bolt through shear modepiezoelectric sensor designs thatelectrically, mechanically, and thermallyisolates the sensing element from thesensor housing. A registered trademark ofWilcoxon Research.

– J –JITTER. Abrupt and spurious shifts in time,amplitude, frequency or phase withwaveforms of either a pulse or continuousnature. Can also be introduced by designas in the case of sample pulse dither.

JOURNAL. Specific portions of the shaftsurface from which rotor applied loads aretransmitted to bearing supports.

– K –KEYPHASOR PHASE REFERENCESENSOR. A signal used in rotatingmachinery measurements, generated by asensor observing a once-per-revolutionevent The keyphasor signal is used inphase measurements for analysis andbalancing. (Keyphasor is a Bently-Nevadaname.)

– L –LATERAL LOCATION. The definition ofvarious points along the shaft axis ofrotation.

LEAD-ZIRCONATE TITANATE. Apiezoelectric ceramic materialcharacterized by a very high activity(sensitivity), broad temperature range, andlong term stability.

LEAKAGE. When power from discretefrequency components extends intoadjacent frequency bands.

LINEAR RANGE. The portion of asensor’s output voltage versus gap curvewithin which the slope (linearity) does notvary significantly from the nominal slope.

LINEARITY. The response characteristicsof a linear system remain constant withinput level. That is, if the response to inputa is A, and the response to input b is B,then the response of a linear system toinput (a + b) will be (A + B). An example ofa nonlinear system is one whose responseis limited by a mechanical stop, such asoccurs when a bearing mount is loose.

LINES. Common term used to describethe filters of a DSA (e.g. 400 line analyzer).

LINE SPECTRUM. The discrete frequencyspectrum produced by the analysis of aperiodic time function. Typically presentedwith fixed bandwidth resolution andnormally contains neither broadband noisenor transient characteristics. Notnecessarily given as a line or bar display.

LOCAL BEARING DEFECT. Relativelysmall damage on a bearing element, forexample, a crack in an outer ring.

LOW-PASS FILTER. A filter whosetransmission band extends from dc to anupper cutoff frequency.

LVDT. Acronym for Linear VariableDifferential Transformer. A contactingdisplacement transducer consisting of amoveable core and a stationarytransformer. The core is attached to thepart to be measured and the transformer isattached to a fixed reference. Often usedfor valve position measurements.

– M –MEMORY LENGTH (PERIOD). The sizeof storage, typically expressed in units oftime for a specified sampling rate. Usuallyrefers to the input memory section of anFFT processing system. Also, sometimesreferred to as block or frame length (SeeFRAME). Defined as the sampling interval(∆t) times the number of samples (N) in thedata block.

MEMORY SYNC. A timing pulsecoincident with the starting address of afixed length, recirculating memory. Oftenrefers to an external sync pulse used toclock the loading of a finite length memorywith respect to an externally free-runningprocess, such as during a signal averagingoperation. Also used to refer to a pulseoutput, occurring once each time a fixedlength memory is updated or recirculated.

MODAL ANALYSIS. The process ofbreaking complex vibration into itscomponent modes of vibration, very muchlike frequency domain analysis breaksvibration down to component frequencies.

MODE SHAPE. The resultant deflectedshape of a rotor at a specific rotationalspeed to an applied forcing function. Athree-dimensional presentation of rotorlateral deflection along the shaft axis.

MODULATION, AMPLITUDE (AM). Theprocess where the amplitude of a signal isvaried as a function of the instantaneousvalue of another signal. The first signal iscalled the carrier, and the second signal iscalled the modulating signal. Amplitudemodulation produces a component at thecarrier frequency, with adjacentcomponents (sidebands) at the frequencyof the modulating signal.

MODULATION, FREQUENCY (FM). Theprocess where the frequency of the carrieris determined by the amplitude of themodulating signal. Frequency modulationproduces a component at the carrierfrequency, with adjacent components(sidebands) at the frequency of themodulating signal.

MOUNTING STUD. A threaded screwused to rigidly attach a motion sensor tothe structure under test.

MOUNTING TORQUE. The optimumtorque applied to the sensor whenmounting with a threaded stud.

MULTIPLEXER. A hardware device thatallows multiple channels to be digitized bya single ADC. In a typical scan, themultiplexer scans the input channelssequentially, pausing only long enoughbetween channels to allow the conversionto be completed.

– N –NATURAL FREQUENCY. The frequencyof free vibration of a system. Thefrequency at which an undamped systemwith a single degree of freedom willoscillate upon momentary displacementfrom its rest position.

NODAL POINT. A point of minimum shaftdeflection in a specific mode shape. Mayreadily change location along the shaft axisdue to changes in residual imbalance orother forcing function, or change inrestraint such as an increased bearingclearance.

NOISE. Any component of a transduceroutput signal that does not represent thevariable intended to be measured.

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OVERLAP PROCESSING. Theprocessing time of an FFT computingdevice is the total amount of time requiredto calculate a desired parameter once theloading of input data memory or memorieshas been accomplished. If the timerequired to process and display the resultsis equal to, or less than, the time requiredto sample the data signals and load inputmemories, the processing is said to beperformed on a real time basis. If theprocessing can be performed significantlyfaster than the time required to sample andload signal inputs, it is then possible toperform multiple analyses of the inputsignals on a segmented basis. Theconcept of performing a new analysis on asegment of data in which only a portion ofthe signal has been updated (some olddata, some new data) is referred to asoverlap processing.

– P –PALOGRAM. Waterfall plot turned 90degrees for easier frequency specific trendidentification.

PASSBAND ANALYSIS. Analysis ofsignals (information) that occur in a known,usually restricted bandwidth. Normallyapplies to frequency domain analysis whichdoes not include dc. (See BASEBAND

ANALYSIS.)

PEAK SPECTRA. A frequency domainmeasurement where, in a series of spectralmeasurements, the one spectrum with thehighest magnitude at a specified frequencyis retained.

PEAK-TO-PEAK VALUE. The differencebetween positive and negative extremevalues of an electronic signal or dynamicmotion. (See AMPLITUDE.)

PERIOD. The time required for a completeoscillation or for a single cycle of events.The reciprocal of frequency.

PERIODIC IN THE WINDOW. Termapplied to a situation where the data beingmeasured in a sampled data system isexactly periodic (repeats an integralnumber of times) within the frame length.Results in a leakage-free measurement indigital analysis instrumentation if arectangular window is used. Real signalsare typically not periodic in the windowunless sampling is synchronized to thedata periodicity.

PERIODIC RANDOM NOISE. A type ofnoise generated by digital measurementsystems that satisfies the conditions for aperiodic signal, yet changes with time sothat devices under test respond as thoughexcited in a random manner. Whentransfer function estimates are measuredwith this type of noise for the excitation,each individual measurement is leakagefree and by ensemble averaging, theeffects of system non-linearities arereduced, thus providing benefits of bothpseudorandom and true random excitation.

PERIODIC WAVEFORM. A waveformwhich repeats itself over some fixed periodof time.

PERIODICITY. The repetitivecharacteristic of a signal. If the period is T(sec), then this results in a discretefrequency or line spectrum with energy onlyat frequencies spaced at 1/T (Hz) intervals.

PHASE. A measurement of the timingrelationship between two signals, orbetween a specific vibration event and akey phasor pulse.

PHASE ANGLE. 1) Time displacementbetween two currents or two voltages (ortheir mechanical analogs) or between acurrent and a voltage measured inelectrical degrees where an electricaldegree is 1/360 part of a complete cycle ofthe frequency at which the measurement ismade. 2) The angle A given by A = tan1 x/y, where x and y are the real and imaginaryparts of a complex number.

PHASE REFERENCE. A signal used inrotating machinery measurements,generated by a sensor observing a once-per-revolution event.

PHASE RESPONSE. The phasedifference (in degrees) between the filterinput and output signals as frequencyvaries; usually expressed as lead and lagreferenced to the input.

PHASE SPECTRUM. Phase-frequencydiagram obtained as part of the results of aFournier transform.

PICKET FENCE EFFECT. In general,unless a frequency component coincidesexactly with an analysis line, there will bean error in both the indicated amplitude andfrequency (where the highest line is takenas representing the frequency component).This can be compensated for, provided it isknown (or assumed) that one is dealingwith a single stable frequency component.

PIEZOELECTRIC. Any material whichprovides a conversion between mechanicaland electrical energy. For a piezoelectriccrystal, if mechanical stresses are appliedon two opposite faces, electrical chargesappear on some other pair of faces.

PIEZOELECTRIC ACCELEROMETER. Asensor which employs piezoelectricmaterials to transduce mechanical motioninto an electrical signal proportional to theacceleration.

PIEZOELECTRIC VELOCITYTRANSDUCER. A piezoelectricaccelerometer with on board signalintegration into velocity.

POINT. An ID established in the database.This ID names an entity which is onespecific and unique data collection location.One POINT is required for each specificmeasurement. Both vibration and processPOINTs can be established.

POLAR PLOT. Polar coordinaterepresentation of the locus of the 1X, 2X,3X, ... vector at a specific lateral shaftlocation with the shaft rotational speed as aparameter.

POLARITY. In relation to transducers, thedirection of output signal change (positiveor negative) caused by motion in a specificdirection (toward or away from thetransducer) in the sensitive axis of thetransducer. Normal convention is thatmotion toward the transducer will producea positive signal change.

PRELOAD, BEARING. The dimensionlessquantity that is typically expressed as anumber from zero to one where a preloadof zero indicates no bearing load upon theshaft, and one indicates the maximumpreload (i.e., line contact between shaftand bearing).

PRELOAD, EXTERNAL. Any of severalmechanisms that can externally load abearing. This includes “soft” preloads suchas process fluids or gravitational forces, aswell as “hard” preloads from gear contactforces, misalignment, rubs, etc.

PROCESS POINT. POINT type used tomonitor values other than vibration.Readings can be manually entered fromthe keyboard collected directly from certaintypes of instruments. Data values can betrended by the software for comparison ofthese process variables with vibration data.

PROCESSING GAIN. In a digital Fourieranalysis system, the improvement insignal-to-noise ratio between periodiccomponents and broadband noise obtainedby transformation to the frequency domainand observation in that domain. The effectis caused by the noise power being spreadout over all frequencies while the discretesignal power remains constant at fixedfrequencies. Doubling the number offrequency resolution lines provides 3 dB ofprocessing gain; (i.e., the noise floor willappear to be reduced by 3 dB in each cell).

PROM. Programmable Read Only Memorycomputer chip.

PSEUDORANDOM NOISE. A periodsignal generated by repeating a datarecord consisting of a series of randomvalues. This noise has a discrete spectrumwith energy at frequencies spaced at 1/record length (sec).

PYROELECTRIC EFFECT. A property ofmost piezoelectric materials whereby achange in temperature produces acorresponding electrical signal.

– R –RADIAL. Direction perpendicular to theshaft centerline.

RADIAL POSITION. The average location,relative to the radial bearing centerline, ofthe shaft dynamic motion.

RANDOM. Describing a variable whosevalue at a particular future instant cannotbe predicted exactly.

RANDOM VIBRATION (RANDOMNOISE). Vibration whose instantaneousvalue cannot be predicted with completecertainty for any given instant of time.Rather, the instantaneous values arespecified only by probability distributionfunctions which give the probable fractionof the total time that the instantaneousvalues lie within a specified range.

– NOTES –

“Random” means not deterministic.

“White” means uncorrelated (flat PSD).

“Gaussian” describes the shape of thePDF.

“Noise” usually means not the signal.

These are all different, though related.

REAL. In a complex signal, the componentthat is in phase with the excitation. Infrequency domain analysis, it is themagnitude of the cosine terms of theFourier series, “Coincident, Co”, as in CO-QUAD analyzer.

REAL-TIME ANALYSIS. Analysis forwhich, on the average, the computingassociated with each sampled record canbe completed in a time less than, or equalto, the record length. In digital analyzers,the functions accomplished during thecomputing time should be specified; (e.g.,Fourier transform, calibration, normalizingby the effective filter bandwidth, averaging,display, etc.).

– N –NORMAL SENSITIVITY. Syn.: AxialSensitivity. The sensitivity of a motionsensor in the direction perpendicular to thesurface of the mounting structure. (SeeTransverse Sensitivity.)

NOTCH FILTER. A band-elimination filterused to prevent the passage of specificfrequencies.

NULLING. Vector compensation at shaftslow roll speed for 1 X electrical/mechanical runout amplitude and phasethat would otherwise distort vibrationmeasurements at higher shaft speeds.

NYQUIST RATE. The Nyquist rate isequal to twice the highest signal frequencyand is the minimum rate at which the datacan be sampled and still avoid aliasing.

– O –OCTAVE. The interval between twofrequencies with a ratio of 2 to 1.

OIL WHIRL/WHIP. An unstable freevibration whereby a fluid-film bearing hasinsufficient unit loading. Under thiscondition, the shaft centerline dynamicmotion is usually circular in the direction ofrotation. Oil whirl occurs at the oil flowvelocity within the bearing, usually 40–49%of shaft speed. Oil whip occurs when thewhirl frequency coincides with (andbecomes locked to) a shaft resonantfrequency. (Oil whirl and whip can occur inany case where a fluid is between twocylindrical surfaces.)

OPTICAL PICKUP. A non-contactingtransducer which detects the level ofreflectively of an observed surface.Provides a light source directed out of thetip of the pickup. When this light isreflected back to the pickup from theobserved surface, a voltage is generated.

ORBIT. The path of the shaft centerlinemotion during rotation. The orbit isobserved with an oscilloscope connectedto X and Y-axis displacement transducers.Some dual-channel DSAs also have theability to display orbits.

ORDER. A multiple of some referencefrequency. An FFT spectrum plotdisplayed in orders will have multiples ofrunning speed along the horizontal axis.Orders are commonly referred to as 1X forrunning speed, 2X for twice running speed,and so on.

ORDER ANALYSIS. The ability to studythe amplitude changes of specific signalsthat are related to the rotation of the deviceunder test. Orders are numbered by theirrelationship to rotational speed, such assecond order = 2 times RPM; third order =3 times RPM.

OSCILLATION. The variation with time ofthe magnitude of a quantity alternatingabove and below a specified reference.(See Vibration.)

OUTER RACE. For rolling bearings, agenerally cylindrical component which ispositioned between the rolling elementsand the bearing housing.

OUTPUT IMPEDANCE. The electricalimpedance as measured from the output ofan electrical system. The impedance atthe output of a sensor must beconsiderably less than that of the input ofthe measurement system.

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– R –REAL TIME RATE. For a DSA, thebroadest frequency span at which data issampled continuously. Real time rate ismostly dependent on FFT processingspeed.

RELATIVE MOTION. Vibration measuredrelative to a chosen reference.Displacement transducers generallymeasure shaft motion relative to thetransducer mounting.

REPEATABILITY. The ability of atransducer or readout instrument toreproduce readings when the same input isapplied repeatedly.

RESOLUTION. The smallest change instimulus that will produce a detectablechange in the instrument output.

RESONANCE. The condition of vibrationamplitude and phase change responsecaused by a corresponding systemsensitivity to a particular forcing frequency.A resonance is typically identified by asubstantial amplitude increase, and relatedphase shift.

ROLL-OFF FREQUENCY. syn.: cutofffrequency. The frequency at which a filterattenuates a pass band gain by 3 dB.

ROLL-OFF RATE. Usually refers to a filtercharacteristic. The best straight-line fit tothe slope of the “filter transmissibilitycharacteristic” in the “transition band,”usually expressed in dB per octave.

ROLLING ELEMENT BEARING. Bearingwhose low friction qualities derive fromrolling elements (balls or rollers), with littlelubrication.

ROLLOFF RATE. Also known as “ultimateslope;” filter’s attenuation rate atfrequencies well outside the passband.Expressed as a positive rate of change ofamplitude (in dB/octave or dB/decade offrequency) for a low-pass filter; as anegative attenuation rate for a high-passfilter.

ROOT MEAN SQUARE IRMSR. Squareroot of the arithmetical average of a set ofsquared instantaneous values. DSAsperform RMS averaging digitally onsuccessive vibration spectra.

ROOT MEAN SQUARE RMS. Square rootof the arithmetic average of a set ofsquared instantaneous values. This can beexpressed by an integral as: where x is thedependent variable, t is the independentvariable and T is the period. (SeeAMPLITUDE.)

ROTOR, FLEXIBLE. A rotor whichoperates close enough to, or beyond itsfirst bending critical speed for dynamiceffects to influence rotor deformations.Rotors which cannot be classified as rigidrotors are considered to be flexible rotors.

ROTOR, RIGID. A rotor which operatessubstantially below its first bending criticalspeed. A rigid rotor can be brought into,and will remain in, a state of satisfactorybalance at all operating speeds whenbalanced on any two arbitrarily selectedcorrection planes.

RPM SPECTRAL MAP. A spectral map ofvibration spectra versus RPM.

RTD. An acronym for Resistance ThermalDevice; a sensor which measurestemperature and change in temperature asa function of resistance.

RUNOUT COMPENSATION. Electroniccorrection of a transducer output signal forthe error resulting from slow roll runout.

Glossary 37

RS-232C. A de facto standard, originallyintroduced by the Bell System, for thetransmission of data over a twisted-wirepair less than 50 feet in length; it definespin assignments, signal levels, and soforth, for receiving and transmittingdevices. Other RS-standards cover thetransmission of data over distances inexcess of 50 feet (RS-422; RS-485).

– S –SAMPLING. The process of obtaining asequence of instantaneous values of afunction at regular or intermittent intervals.

SAMPLING RATE. The rate, in samplesper second, at which analog signals aresampled and then digitized. The inverse ofthe sampling interval.

SCALE FACTOR. The Factor by whichthe reading of an instrument must bemultiplied in order to result in the true finalvalue, when a corresponding (but inverse)scale factor was used initially to bring thesignal amplitude within range of theinstrument.

SEISMIC. Refers to an inertiallyreferenced measurement or ameasurement relative to free space.

SCREENING. Transformation of ameasurement to such a form that itenhances the information about a certaindefect.

SEE™ (SPECTRAL EMITTED ENERGY).Technology developed by SKF to measurehigh frequencies (250-350 kHz) associatedwith metal-to-metal contact in rollingelement bearings.

SEISMIC TRANSDUCER. A transducerthat is mounted on the case or housing of amachine and measures casing vibrationrelative to free space. Accelerometers andvelocity transducers are seismic.

SENSITIVITY. The ratio of magnitude ofan output to the magnitude of a quantitymeasured (for example, sensitivity ofmeasuring voltage with an oscilloscope isspecified in centimeters/volt or divisions/volt). Also, the smallest input signal towhich an instrument can respond.

SENSOR. A transducer which senses andconverts a physical phenomenon to ananalog electrical signal.

SHEAR MODE ACCELEROMETER. Anaccelerometer design which stresses thepiezoelectric element in the shear direction:i.e. the electrode faces move parallel toeach other. (See BENDER BEAM

ACCELEROMETER, COMPRESSION

MODE ACCELEROMETER.)

SHOCK LIMIT. The maximum amount ofshort duration mechanical shock that asensor can be subjected to before thepossibility of permanent damage canoccur. (See MECHANICAL SHOCK.)

SIDEBANDS. Additional frequenciesgenerated by frequency modulation.

SIDE LOBE. A response separated infrequency from the main or desiredresponse. Usually refers to a filter shape,particularly in digital filters that havecomplex structure (many notches andpeaks) in the filter transition band

SIGNAL ANALYSIS. Process of extractinginformation about a signal’s behavior in thetime domain and/or frequency domain.Describes the entire process of filtering,sampling, digitizing, computation, anddisplay of results in a meaningful format.

SIGNAL CONDITIONER. A device placedbetween a signal source and a readoutinstrument to change the signal.Examples: attenuators, preamplifiers,signal converters (for changing oneelectrical quantity into another, such asvolts to amps or analog to digital), andfilters.

SIGNAL-TO-NOISE RATIO. A measure ofsignal quality. Typically, the ratio ofvoltage or power of a desired signal to theundesired noise component measured incorresponding units.

SIGNATURE. A vibration frequencyspectrum which is distinctive and special toa particular machine or component, systemor subsystem at a specific point in time,under specific machine operatingconditions. Used for historical comparisonof mechanical condition over the operatinglife of the machine.

SIGNATURE ANALYSIS. The methodwhereby a physical process or device isidentified in terms of the invariantfrequency characteristics of the signal itgenerates.

SIGNATURE ANALYZER. Comparesstored patterns (signatures) againstreceived patterns.

SIMULTANEOUS SAMPLE and HOLD. Indata acquisition systems, the technique ofusing separate sample and hold amplifiersfor each channel. This allowssimultaneous sampling on all channels,thereby eliminating any SKEW due to useof a multiplexer.

SLEW RATE. The large-signal rate-of-change of output of a filter under specificoperating conditions, expressed in volts/microsecond; expresses the fastest rate atwhich a filter output can execute voltagelevel output excursions to within predictedtolerances.

SLOW ROLL SPEED. Low rotative speedat which dynamic motion effects fromforces such as imbalance are negligible.

SPALL. In rolling bearings, a flake or chipof metal removed from one of the bearingraces or from a rolling element. Spalling isevidence of serious bearing degradationand may be detected during normalbearing operation by observing increasesin the signal amplitude of the highfrequency vibrations signals.

SPECTRAL MAP. A three-dimensionalplot of the vibration amplitude spectrumversus another variable, usually time orRPM.

SPECTRUM. The distribution of theamplitude of the components of a timedomain signal as a function of frequency.

SPECTRUM ANALYZER. An instrumentwhich displays the frequency spectrum ofan input signal.

STATIC DATA. Data which describes thequantitative characteristics of themeasured parameter. Static data can alsoinclude quantitative values describing theconditions under which the parameter wasmeasured. For condition monitoringpurposes, static data is typically presentedin various forms of trend graphs anddisplays/lists of current values. Examplesof static data include vibration amplitude,phase lag angle, frequency, vector,average shaft position, shaft rotativespeed, time, date, monitor alarm and OKstatus.

STEADY STATE DATA. Data (static and/or dynamic) acquired from a machinewhich is on-line, under (relative) constantoperating conditions (shaft rotative speed,load).

STIFFNESS. The spring-like quality ofmechanical and hydraulic elements toelastically deform under load.

STRAIN. The physical deformation,deflection, or change in length resultingfrom stress (force per unit area).

STRAIN GAUGE. A transducer whichreacts to changes in load, typically throughchanges in resistance.

SUBHARMONIC. Sinusoidal quantity of afrequency that is an integral submultiple ofa fundamental frequency.

SUBSYNCHRONOUS. Component(s) of avibration signal which has a frequency lessthat shaft rotative frequency.

SYNC PULSE. A trigger pulse which isused to synchronize two or moreprocesses.

SYNCHRONOUS. The component of avibration signal that has a frequency equalto the shaft rotative frequency (1X).

SYNCHRONOUS TIME DOMAIN. Adynamic amplitude vs. time graph (timedomain) of data averaged in relation to asynchronous trigger pulse.

SYSTEM IDENTIFICATION. The processof modeling a dynamic system andexperimentally determining values ofparameters in the mathematical modelwhich best describes the behavior of thesystem.

– T –TEMPERATURE RANGE. Thetemperature span, given by thetemperature extremes, over which thesensor will perform without damage.Specifications within the temperature rangemay vary as a function of temperature.

TEMPERATURE RESPONSE. A measureof the change in a quantity, usuallysensitivity, as a function of temperature.

THERMOCOUPLE. A temperaturesensing device comprised of two dissimilarmetal wires which, when thermally affected(heated or cooled), produce a proportionalchange in electrical potential at the pointwhere they join.

THRESHOLD. The smallest change in ameasured variable that will result in ameasurable change in an output signal.

THROUGH-PUT. Amount of workperformed by a system (e.g., number ofbatch jobs per hour processed by acomputer).

THRUST POSITION. (See AXIAL

POSITION.)

TIME AVERAGING. In a DSA, averagingof time records that results in reduction ofasynchronous components.

TIMEBASE DISPLAY/PLOT. Apresentation of instantaneous amplitude ofa signal as a function of time. A vibrationwaveform can be observed on anoscilloscope in the time domain.

TIME DOMAIN. A dynamic amplitudeversus time graph.

TIME LAG. In correlation analysis onecalculates an integral of the product of onesignal and a temporally displaced signal.The time difference between the twosignals is referred to as the time-lag.

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TSI. Acronym for Turbine SupervisoryInstrumentation. A TSI system is acontinuous monitoring system generallyused on turbogenerator sets. It can includesuch measurement parameters as shaftradial vibration, axial thrust position,differential expansion, case expansion,valve position, and shaft rotative speed.The TSI system consists of measurementsensors, monitors, interconnecting wiringand a microprocessor-based monitoring/data acquisition system.

TTL (TRANSISTOR-TRANSISTORLOGIC). A logic family characterized byhigh speeds, medium power consumption,and wide usage.

– U –UNBALANCE. (See IMBALANCE.)

UNIFORM WINDOW. In a DSA, a windowfunction with uniform weighting across thetime record. This window does not protectagainst leakage, and should be used onlywith transient signals contained completelywithin the time record.

UPLOAD. Transferring collected data fromthe MICROLOG to the host computer.

– V –VALVE POSITION. A measurement of theposition of the process inlet valves on amachine, using expressed as a percentageof the valve opening; zero percent is fullyclosed, 100 percent is fully open. Oftenincorporated as a measured parameter onsteam turbines.

VANE PASSING FREQUENCIES. Apotential vibration frequency on vanedimpeller compressors, pumps, and othermachines with vaned rotating elements. Itis represented by the number of vanes (onan impeller or stage) times shaft rotativefrequency.

VECTOR. A quantity which has bothmagnitude and direction (phase).

VELOCITY. The time rate of change ofdisplacement. This if often expressed asV, x or dx/dt; velocity leads displacementby 90 degrees in time. Typical units forvelocity are inches/second or millimeters/second, zero to peak. Velocitymeasurements are usually obtained with anaccelerometer and integrated to velocity ora mechanically activated velocitytransducer and are used to evaluatemachine housing and other structuralresponse characteristics. Electronicintegration of a velocity signal yieldsdisplacement.

VELOCITY SENSOR. Anelectromechanical transducer, typically ofseismic design, used for measuring bearinghousing and other structural vibration. Thistransducer measures absolute vibration,relative to a fixed point in space.

VIBRATION. Magnitude of cyclic motion;may be expressed as acceleration,velocity, or displacement. Defined byfrequency and timebase components.

VIBRATION LIMIT. The maximum amountof vibration that a sensor can be subjectedto before the possibility of permanentdamage can occur.

– W –WATERFALL PLOT. (See SPECTRAL

MAP.)

WAVEFORM. A presentation or display ofthe instantaneous amplitude of a signal asa function of time. A vibration waveformcan be observed on an oscilloscope in thetimebase mode.

WINDOW. When a portion only of a recordis analyzed, that portion is called a window.A window can be expressed in either thetime domain or in the frequency domain,although the former is more common. Toreduce the edge effects, which causeleakage, a window is often given a shapeor weighting function. A window in the timedomain is represented by a multiplicationand, hence, is a convolution in thefrequency domain. A convolution can bethought of as a smoothing function. Thissmoothing can be represented by aneffective filter shape of the window; energyat a frequency in the original data willappear at other frequencies as given by thefilter shape. Since time domain windowscan be represented as a smoothingfunction in the frequency domain, the timedomain windowing can be accomplisheddirectly in the frequency domain.

– Z –ZERO TO PEAK VALUE. One-half of thepeak to peak value. (See AMPLITUDE.)

ZOOM. Feature to magnify portions of aselected spectrum plot for more detailedexamination.

ZOOM ANALYSIS. A zoom analysis is atechnique for examining the frequencycontent of a signal with a fine resolutionover a relatively narrow band offrequencies. The technique basically takesa band of frequencies and translates themto a lower band of frequencies, where thesignals can be decimated to reduce thesample size. A standard analyzer can thenbe used to analyze the data.

– NOTE –

That the increased resolution of thistechnique requires a corresponding

increase in the time record length. Thesample rate is decreased by decimation,to reduce the number of samples in the

time window, only after thedemodulation.

38 Glossary

– T –TIME RECORD. In a DSA, the sampledtime data converted to the frequencydomain by the FFT. Most DSAs use a timerecord of 1024 samples.

TIME RECORD LENGTH. The total lengthof time over which a time history isobserved. This total time may be brokenup into several shorter data blocks.

TIMESTAMP. Current date assigned attime of data collection or event.

TIME SYNCHRONOUS. A data samplingand/or processing technique in which thebeginning or ending of a data block issynchronized with an external event.

TIME WINDOW. The time record is oftendivided into segments and each segment isanalyzed as a unit or frame of data. Eachframe is called a block or time window.(See WINDOW.)

TORQUE. A measure of the tendency of aforce to cause rotation, equal to the forcemultiplied by the perpendicular distancebetween the line of action of the force andthe center of rotation.

TORSIONAL VIBRATION. Amplitudemodulation of torque measured in degreespeak-to-peak referenced to the axis ofshaft rotation.

TRACKING FILTER. A low-pass orbandpass filter which automatically tracksthe input signal. A tracking filter is usuallyrequired for aliasing protection when datasampling is controlled externally.

TRANSDUCER. (See SENSOR.)

TRANSIENT ANALYSIS. When theexcitation of a system is of finite duration,the analysis of the data is a transientanalysis. A transient analysis can also beused to study the change from one steady-state to a second steady-state condition.

TRANSIENT VIBRATION. Temporarilysustained vibration of a mechanicalsystem. It may consist of forced or freevibration or both. Typically this isassociated with changes in machineoperating condition such as speed, load,etc.

TRANSVERSE SENSITIVITY. syn.: CrossAxis Sensitivity. The parameter quantifyingthe unwanted output signal picked up by amotion transducer when subjected tomotion perpendicular to the normal axis ofoperation. The transverse sensitivity isusually given in terms of the maximumpercent of the normal axis sensitivity.

TRIBOELECTRIC EFFECT. Electricalnoise caused by cable motion. When acable is bent, the displacement of oneconductor relative to the other introduces aspurious signal. Particularly problematicwith high impedance electrical systems,such as charge mode accelerometers.

TRIGGER. Any event which can be usedas a timing reference. In a DSA, a triggercan be used to initiate a measurement.

TRIP MULTIPLIER. That function providedin a monitor system to temporarily increasethe alarm (Alert and Danger) set pointvalues by a specific multiple. This functionis normally applied by manual (operator)action during start-up to allow a machine topass through critical speed ranges withoutnuisance monitor alarm indications.

Trademarks used in this publication.

RYTON® is a registered trademarkof Phillips Chemical Company.

TEFLON® is a registered trademarkof DuPont.

UL® is a registered trademark ofUnderwriters Laboratories Inc.

CSA® is a registered trademark ofCanadian Standards Association.

National Electric Code® is aregistered trademark of NationalFire Protection Association.

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Conversion Charts 39

Sinusoidal Motion (zero–peak).

Sinusoidal Wave Forms Multiplier x (A = xB).

Average Value = 0.637 x Peak Value

RMS Value = 0.707 x Peak Value

Peak Value = 1.414 x RMS Value

Peak to Peak Value = 2.000 x Peak Value

Peak to Peak Value = 2.828 x RMS Value

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Peak Peak to Peak RMS Average

Peak 1.000 0.500 1.414 1.570

Peak to Peak 2.000 1.000 2.828 3.140

RMS 0.707 0.354 1.000 1.110

Average 0.637 0.319 0.901 1.000

A

B

Average RMS Peak

Peakto

Peak

Conversion ChartsAcceleration

1 g = 32.174 ft/sec2

1 g = 9.807 m/sec2

1 in/sec2 = 0.0254 m/sec2

Displacement1 mil = 0.001 in1 mil = 0.0254 mm1 in = 25.4 mm1 cm = 10 mm

Frequency1 Hz = 1 cps1 Hz = 0.159 rad/sec1 Hz = 60 rpm1 rpm = 0.0167 Hz1 rpm = 1 cpm

Temperature°F °C-58 -50-40 -40+32 0+77 +25

+176 +80+248 +120+392 +200+500 +260

°F = (°C) 9/5 + 32°C = 5/9 (°F – 32)

Decibel ScaledB Gain60 1000.00040 100.00020 10.00010 3.1606 2.0003 1.4101 1.1200 1.000-1 0.891-3 0.708-6 0.501

-10 0.316-20 0.100-40 0.010-60 0.001

dB = 20 log (Vout/Vref)

Vout/Vref = log-1 (dB/20)

Weight1 ounce = 28.35 grams1 kilogram = 2.205 lbs1 Newton = 0.2245 lbs

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Displacement (D) Velocity (V) Acceleration (A)(in) (in/sec) (g)

Displacement (D) ---------- D = 0.159 V/ƒ D = 9.78 A/ƒ2(in)

Velocity (V) V = 6.28ƒD ---------- V = 61.4 A/ƒ(in/sec)

Acceleration (A) A = 0.102 ƒ2D A = 0.0163 ƒ V ----------(g)

ƒ = frequency, Hz

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Sensor Selection ChecklistFor assistance in selecting a vibration sensor, specific application and measurement requirements should be provided tothe application engineer. Completing the checklist below will help ensure that the proper sensor is chosen.

Describe the Vibration Measurement Application (check all that apply):INDUSTRY MACHINERY TYPE MEASUREMENT TYPE

Pulp and Paper Cooling Towers Balancing

Petrochemical Shipboard Machinery Diagnostic Testing

Power Plant Rotating Machinery Trend Analysis

Oil Exploration Bearings Predictive Maintenance

Mining Pumps Alarm Condition

Military Turbines High Frequency Testing

Automotive Compressors Other _______________________

Laboratory Research Engines

Microelectronics Machine Tools

Civil Engineering Other _______________________

Other _______________________

Please describe the application: ________________________________________________________________________________________________

_________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________

Dynamic Measurement Requirements of the Application:What is the approximate vibration amplitude level to be measured? __________ g peak (rms), ______ in/sec/peak (mm/sec/rms),______ mil peak (µm peak)

What is the maximum vibration amplitude level expected to be present? ______ g peak (rms), ______ in/sec/peak (mm/sec/rms),______ mil peak (µm peak)

What is the minimum vibration amplitude level of interest? ________________ g peak (rms), ______ in/sec/peak (mm/sec/rms),______ mil peak (µm peak)

What is the maximum frequency of interest? ____________ Hz, ____________ RPM

What is the minimum frequency of interest? ____________ Hz, ____________ RPM

Mechanical and Chemical Environment of the Application:Continuous temperature range (minimum to maximum): __________ to __________ °C, __________ to __________ °F

Intermittent temperature range (minimum to maximum): __________ to __________ °C, __________ to __________ °F

What is the expected humidity level? _______________ % relative

What fluids contact the accelerometer? _________________________________________________________________________________________

If submerged, what fluid pressure will be present? _______________ psi/nm

Are high amplitude mechanical signals present? (i.e. Steam valve release, gear chatter, impacts) ___________________________________________

What is the highest shock level expected to be present? _______________ g peak

What chemicals or gases contact the accelerometer or cable? (Check all that apply) Water (i.e. salt water, heavy water, steam) Describe: ____________________________________________________________________________

Halogens (i.e. chlorine, fluorine, halogenated compounds) Describe: _______________________________________________________________

Gases (i.e. ozone, chemical fumes) Describe: _________________________________________________________________________________

Acids (i.e. hydrochloric, sulfuric, nitric) Describe: ______________________________________________________________________________

Bases (i.e. ammonia, caustic soda) Describe: __________________________________________________________________________________

Solvents (i.e. methyl ethyl keytone, freon, alcohol) Describe: _____________________________________________________________________

Fuels (i.e. gasoline, kerosene) Describe: ______________________________________________________________________________________

Oil (i.e. lubricating, crude) Describe: ________________________________________________________________________________________

Detergents Describe: _____________________________________________________________________________________________________

Other Chemicals Describe: ________________________________________________________________________________________________

40 Sensor Selection Checklist

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SKF Reliability Systems5271 Viewridge Court

San Diego, California 92123 USA

Telephone: (+1) 858-496-3400

FAX: (+1) 858-496-3531

Web Site: www.skf.com/reliability

Although care has been taken to assure the accuracy of the data compiled in this publication, SKF does

not assume any liability for errors or omissions. SKF reserves the right to alter any part of this

publication without prior notice.

• SKF is a registered trademark of SKF.

• All other trademarks are the property of their respective owners.

CM2005 (Revised 11-99)

Copyright © 1999 by SKF Reliability Systems. ALL RIGHTS RESERVED.

SKF Reliability Systems