Process Control Terminology

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process control terminology

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A

Absolute Pressure Sensor-a sensor which measures input pressure in relation

to zero pressure (a total vacuum on one side of the diaphragm).

Actuator-mechanism of the switch or switch enclosure which operates the

contacts.

Acceleration-the rate of change of velocity. Acceleration has two characteristics:

magnitude and direction.

Accuracy- a comparison of the actual output signal of a device to the true value

of the input pressure. The various errors (such as linearity, hysteresis,

repeatability and temperature shift)* attributing to the accuracy of a device are

usually expressed as a percent of full scale output (Span)

Alignment-placing the emitter (light source) and receiver (photoreceiver or

reflector) so as to direct the maximum amount of light on the photosensor. At

long distances, when the light beam has widened, the receiver should be centered

in the beam to lessen the chance of the emitter and receiver drifting out of

alignment due to vibration or shock.

Alternating Current (AC)-one that reverses at regularly recurring intervals of

time and has alternately positive and negative values.

Ambient-in the area. 1) light-Light in the area of the photosensor, but not

originating with the control light source. Ambient light can adversely affect non-

modulated control operation, and should be screened, if possible, from the

sensor; 2) Temperature-average temperature of surrounding medium such as

water, air, or earth, into which the heat of the equipment is dissipated.

Analog Output-having the property of being continuously variable, as opposed

to having discrete states.

AND Logic-an output is produced only when all inputs are present.

Analog Output- an electrical output from a sensor that changes proportionatelywith any change in input pressure.

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Anode-the switch contact connected to the positive terminal of the power supply.

Aperture-most often an external cap (with a small opening) placed over the

receiver lens to help detect small objects. It lets even a small object block enough

light to be detected. Also, an internal aperture in most receivers reduces theeffect of off-axis ambient light.

Arc-one of several kinds of visible electrical discharge between separated

contacts of a switch. It is primarily a stream of electrons and is accompanied by

incandescent metal vapor.

Attenuation-loss or reduction of beam intensity as a result of environmental

factors, dust, humidity, steam etc.

Auto Zeroing Technique- a method used to automatically set the null point on

a pressure sensor. This is usually done by using a microprocessor to open a

solenoid valve at a predetermined time interval. This references atmospheric

pressure to both sides of the pressure sensor chip. The microprocessor reads the

output voltage and makes that the new null point. This method is used to

eliminate errors due to null offset and null temperature shift.

Auxiliary Actuator-a mechanism, sold separately, to provide basic switches with

easier means of operation and adjustment and adapt switches to different

operating motions by supplying supplemental overtravel.

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B

Basic Switch-a self contained switching unit. It can be used alone, gang-

mounted, built into assemblies or enclosed in metal housings.

Bifurcated Contact-a movable or stationary contact which is forked or divided to

provide two pairs of mating contact surfaces connected in parallel, instead of a

single pair of mating surfaces.

Bidirectional Differential Pressure Sensor-a differential pressure sensor

allowing the greater input pressure to be applied to either pressure port.

B.F.S.L. (Best Fit Straight Line)-a method for defining linearity. A straight line

placed on a sensor output curve such that half the data points lie above and half

below that line. The method for determining B.F.S.L., is the sum of least squares.

Bridge Resistance- see Input Impedance and Output Impedance.

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Break-to open an electrical circuit.

Break Distance-the minimum distance between separated mating contacts in

their fully open position.

Burst pressure-the specified pressure which will rupture the sensing element

but not the sensor case.

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C

Cascade-to combine logic circuitry to get more complex logic or timing control.

(Inputs and outputs are wired in series.)

Calibration-a test during which known values ofMeasurandare applied to the

device under test and corresponding output readings are recorded under specified

conditions.

Calibration Curve-a graphical representation of the calibration record.

Calibration Cycle-the application of known values of Measurand and recording of

corresponding Output readings over the full or the specified portion of the Range,

in an ascending and descending direction.

Catalyst-a substance which changes the rate of a chemical reaction but is itself

not changed. Switch contact material sometimes acts as a catalyst, accelerating

the formation of polymers on the contact surface.

Cathode-the switch contact connected to the negative terminal of the power

supply.

Characteristics-This term is used by MICRO SWITCH in a restricted sense and

refers only to switch operating characteristics such as pretravel, operating force,

etc.

Clean Air-ideal conditions. Climate controlled or sterile area.

Chip-a die (unpackaged semiconductor device) cut from a silicon wafer,

incorporating semiconductor circuit elements such as resistors, diodes,

transistors, and/or capacitors.

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Compensation-procedure of providing a supplemental device, circuit, or special

materials to conunteract known sources of error (e.g., ambient temperature

change). Compensation is often related to temperature compensation only.

Complementary Output-both N.O. and N.C. outputs are available for use. Acircuit that provides sink or source capability with a single input. Output that can

be both light operated and dark operated. (Also known as 4-wire DC controls.)

Control-the complete system; sensor, amplifier, output.

Control Base-unit remote from sensor in which amplification and conditioning of

the input signal takes place. Usually contains a power supply and an output

device.

Convergent Beam-A variation of the diffuse scanning mode. A photoelectric

control whose optical system is key to its operation. It simultaneously focuses

and converges a very small, intense beam to a fixed-focal point in front of the

control. The control is essentially blind a short distance before and beyond this

focal point. Convergent beam scanning is used to detect the presence or absence

of small objects while ignoring nearby background surfaces.

Convertible Output-output that can be wired either as Normally Open or

Normally Closed, but not at the same time.

Corrective Factor-the mathematical factor that, when multiplied by the sensing

distance of a given sensor, will adjust sensing distance for the different metals

being used as targets.

Current-time value of movement of free electrons. One ampere equals one

coulomb per second. Conventional reference is opposite to direction of actual

electron movement.

Current Consumption-the amount of current required to power a sensor or

control (excluding load). See supplycurrent.

Current Sinking-an output type such that when it is On, current flow is from the

load into the device's output, then to ground. Output is Normally High. The

sensor "sinks" current from the load through the sensor to ground. The load is

connected between the positive lead of the supply and the output lead of the

sensor.

Current Sourcing-an output type such that when it is On, current flow is from

the device into the load. Output is Normally Low. The sensor "sources" current to

the load. The load is connected between the output lead and the negative groundlead of the supply.

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D

Dark Operated (D.O.)-control operating mode in which the output (load) is

energized when the light is blocked (retro/thru scan) or object not present

(diffuse), the photosensor is dark.

Dead Break-Imperfect snap action in which the normally closed circuit of the

switch opens before the plunger reaches the operating point, or the normally

open circuit opens before the plunger reaches the release point.

Dead Make-Imperfect snap action in which a switch fails to close its circuit when

the plunger reaches the operating or release point.

Diaphragm-the membrane of material that remains after etching a cavity into

the silicon sensing chip. changes in input pressure cause the diaphragm to

deflect.

Dielectric-the term dielectric is almost synonymous with electrical insulation,

which can be considered the applied form of the dielectric.

Dielectric Breakdown-rupture of insulation material when the electric stress

exceeds the dielectric strength of the material.

Dielectric Strength-the maximum potential gradient that a material can

withstand without rupture. As a material property it usually is calculated by

dividing the breakdown voltage by the thickness of the material between a pair of

test electrodes. The term often is applied to switches to mean the maximum

voltage a switch can withstand between specified terminals or between terminals

and ground without leakage current exceeding a specified value.

Differential Pressure Sensor-a sensor which is designed to accept

simultaneously two independent pressure sources. The output is proportional to

the pressure difference between the two sources.

Differential Travel-the distance from the operating point to the release point.

Diffusion-a thermochemical process whereby controlled impurities are

introduced into the silicon to define the piezoresistors. Compared to ion

implantation, it has two major disadvantages: 1) the maximum impurity

concentration occurs at the surface of the silicon rendering it subject to surface

contamination, and making it nearly impossible to produce buried piezoresistors;

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2) control over impurity concentrations and levels is about one thousand times

poorer than obtained with ion implantation.

Diffuse Scan-a reflective scanning technique in which reflection from a near-by

non-shiny surface illuminates the photosensor in the receiver. Sometimes calledproximity scan because of the required nearness of the light source and

photosensor to reflecting surface. Also used to detect color contrast as in

registration control.

Digital Circuit-a circuit that has only two stable states, operating in the manner

of a switch; that is, it is either On or Off.

Digital Output-output that is of only two stable states, appearing in the manner

of a switch; that is, it is either On or Off or High or Low (i.e., high voltage or low

voltage).

Direct Current (DC)-a unidirectional current in which changes in value are so

small that they may be neglected. As ordinarily used, the term designates a

practically non-pulsating current.

Disable-to prevent the output despite an input signal. A wiring terminal for this

purpose is provided on most MICRO SWITCH control bases. The disabling circuit

may receive its signal from the current sinking output of a photoelectric logic

card, or modulated LED control, or from an electromechanical limit switch, etc.

Disabling is used to prevent false or unwanted signals from triggering the control.

Double Break Contacts-(Twin break). This breaks the circuit in two places.

Referred to as form Z circuitry also.

Double-Pole Double Throw (DPDT)-switches which make and break two

separate circuits. This circuit provides a normally open and normally closed

contact for each pole.

Drift-an undesired change in output over a period of time, which is not a function

of any input pressure change.

Drift of an Operating Characteristic-an inexact term referring in a general way

to the degree of instability of a plunger force or travel characteristic under

specified conditions and during a specified number of cycles of switch operation.

Dry Circuit-slang expression meaning a low energy circuit. Although many

individuals and groups have assigned current and voltage values to "dry circuits"

there is at present no general agreement as to what the values should be.

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E

Effective Sensing Distance-the difference between nominal sensing distance

and the % manufacturing tolerance.

Electrical Life-life of a switch under a specified combination of electrical load,

actuation, environment and criterion of failure. Synonymous with switch life.

Enable-the opposite of disable. To allow output in response to an input signal. We

often speak of one light source-photoreceiver pair (the "gating" pair) enabling a

second pair (the "inspect" pair).

Enclosed Switch-a basic switch unit (contact block) enclosed in a durable metal

housing. The enclosure protects the switching unit, provides mounting means,

and fitting for conduit connection.

End points-the Outputs at the specified upper and lower limits of the Range.

Environment-Proof Switch-a switch which is completely sealed to ensure

constant operating characteristics. Sealing normally includes and "O" ring on

actuator shaft and fused glass-to-metal terminal seals or complete potting and an

elastomer plunger-case seal.

Erosion, Contact-a general loss of material from one or both working surfaces of

a pair of mating contacts, as a result of switching an electrical load.

Error-the algebraic difference between the indicated value and the true value of

the input pressure. Usually expressed in percent of full scale output, sometimes

expressed in percent of the sensor output reading.

Error Band-the band of maximum deviations of the output values from a

specified reference line or curve due to those causes attributable to the sensor.

Usually expressed as "+ -% of full scale output." The error band should be

specified as applicable over at least two calibration cycles, so as to include

repeatability, and verified accordingly.

Excess Gain-the ratio of optical power available at a given emitter-to-receiver

range to the minimum optical power required to trigger the receiver.

Excitation-the external source of energy (e.g., electrical voltage or current)

applied to a sensor for its operation.

Explosion-Proof-having the ability to contain an explosion within the sensor orhousing if it were to occur.

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Explosion-Proof Switch-a UL listed switch capable of withstanding an internal

explosion of a specified gas without ignition of surrounding gases.

Extreme Contamination-coal bins, residue on lens.

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F

Fall Time-a measure of the time required for the output voltage of a circuit to

change from a high voltage level to a low voltage level, once a level change has

started (90% to 10%).

False Pulse-an improper change of state of the output, usually associated withTurn-Off or Turn-On.

False Pulsing-circuitry designed to clamp output Off until the power supply has

time to reach proper voltage level. Typically 200-500 msec.

False Pulse Protection-circuitry designed to clamp output Off until the power

supply has time to reach proper voltage level. Typically 200-500 msec.

Fiber Optics-transparent fibers of glass or plastic used for conducting and

guiding light energy. Fiber optics are used in photoelectrics as light pipes

consisting of a bundle of small optical fibers (glass) or single strand (plastic)

housed inside a flexible sheathing.

Force, Contact-the force holding closed contacts together.

Force Differential-the difference between the operating force and the release

force.

Free Position of the Plunger-the position of the plunger when there is no

external force other than gravity applied to it.

Frequency, Natural-the frequency of free (not forced) oscillations of the sensing

element of a fully assembled sensor.

Frequency Output-an output in the form of frequency which varies as a function

of the applied pressure.

Full Overtravel Force-the force required to depress the plunger of a switch to

the full overtravel point.

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Full Overtravel Point-that position of the plunger beyond which further

overtravel would cause damage to the switch or actuator.

Full Scale Output (Span)-the algebraic difference between output curve end

points (outputs at specified upper and lower output limits).

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G

Gage Factor-a measure of the ration of the relative change of resistance to the

relative change in length of a resistive strain sensor (strain gage).

Gage Pressure-a form of differential pressure measurement in whichatmospheric pressure is used as a reference.

Gravity Unit-one gravity unit (abbreviated g) is an acceleration of 32.2 feet per

second per second.

Ground-a conducting path, intentional or accidental, between an electric circuit

or equipment and the earth, or some large conducting body serving in place of

the earth (a voltage reference).

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H

Hall Effect Technology-the description given to the following phenomena; when

a semiconductor, through which a current is flowing, is placed in a magnetic field,

a difference in potential (voltage) is generated between the two opposed edges of

the conductor in the direction mutually perpendicular to both the field and the

conductor. Typically used in sensing magnetic fields.

Hardwired-physically interconnected and intended for a specific purpose.

Hardwired logic is essentially unalterable.

Hazardous Location-defined as an area in which flammable or combustible

mixtures are present.

Head-On-a condition whereby the target approaches the sensing face of the

proximity sensor with its center along the sensing face.

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High Contamination-heavy particle laden air, extreme washdown environments,

grain elevators.

Hermetically Sealed Switch-a switch completely sealed to provide constant

operating characteristics. All junctures made with metal-to-metal or glass-to-metal fusion.

Hysteresis, Switching-the principle associated with sensors, such that the

operate point is not at the same level as the release point. In solid state sensors,

it is accomplished electrically. In mechanical switches, it results from the storing

of potential energy before the transition occurs. Also known as differential, and is

usually expressed as a percentage of the operate point (e.g. 3-15%).

I

Immediate Response-control transfers On/Off state immediately when target

enters the detection range, and reverses state immediately when target leaves

detection range.

Inductive Technology-technology based on inductance, the property of an

electric circuit by which an electromotive force is induced in it by a variation of

current, either 1) in the circuit itself, or 2) in a neighboring circuit.

Infrared (IR)-the invisible radiation (as opposed to visible light) that certain

LEDs emit. Standard MICRO SWITCH modulated LED controls have infrared

emitting LEDs.

Input-1) The device or collective set of devices used for bringing data into

another device; 2) The signal or stimulus put into a circuit to make the output do

something.

Input Impedance-the impedance (presented to the excitation source) measured

across the excitation terminals of a sensor.

Input Signal Duration-a length of time the light beam is blocked (in dark

operated mode), or uniterrupted (in light operated mode). Or, the length of time

a target is within the operating range.

Insulation Resistance-the resistance measured between specified insulated

points on a sensor when a specified DC potential is applied at room conditions.

Insulator-a non-conducting support for an electric conductor. A material that

does not conduct electricity.

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Integrated Circuit (IC)-an interconnected array of active and passive elements

integrated within a single semiconductor substrate or other compatible material,

and capable of performing one complete electronic function.

Interface-a common boundary between electronic systems, or parts of a singlesystem.

Interface Circuit-a circuit that links one type of device with another. It's

function is to produce the required current and voltage levels for the next stage

of circuitry from the previous stage.

Interrogate (Gate)-a function usually performed by gating light source-

photoreceiver pair; asking (interrogating) whether a certain condition has been

met (for example, proper fill level in boxes moving along a conveyor), and

thereby enabling or disabling an inspect light source-photoreceiver pair (which

will count only full boxes).

Intrinsically Safe-limits electrical/thermal energy to levels incapable of causing

ignition. External barriers are required.

IP-European environmental ratings similar to USA NEMA ratings.

Ion Implantation-a process whereby impurity ions are accelerated to a specific

energy level and impinged upon the silicon wafer. The energy level determines

the depth to which the impurity ions penetrate the silicon. Impingement time

determines the impurity concentration. Thus, it is possible to independently

control these parameters, and buried piezoresistors are easily produces. Ion

implantation is increasingly used throughout the semiconductor industry to

provide a variety of products with improved performance over those produced by

diffusion.

IR-Infrared: A portion of the spectrum of light which is not visible (wavelengths

which extend beyond 770nm).

IRED-Infrared-Emitting Diode: a diode capable of emitting radiant energy in the

infrared region of the spectrum.

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J

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K

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L

Laser Trimming (Automated)-a method for adjusting the value of thick film

resistors using a computer-controlled laser system.

Latching Logic-signal modification that causes the output to be energized and

remain energized (maintain output). Latched output may be immediate or

delayed. Usually, the latch is released by closing a circuit between the reset

(RS/D) terminal and ground.

Leakage Current-small current flowing through or leaking from the output

device in the Off state due to semiconductor characteristics.

Leakage Rate-the maximum rate at which a fluid is permitted or determined to

leak through a seal. The type of fluid, the deferential pressure across the seal,

the direction of leakage, and the location of the seal must be specified.

Least Squares Line-the straight line for which the sum of the squares of the

residuals (deviations) is minimized. This method is used to calculate B.F.S.L.

linearity.

LED (Light Emitting Diode)-a solid state light source that emits variable light,

or (in MICRO SWITCH modulated LED controls) invisible, infrared radiation.

Light Operated (L.O.)-control operating mode in which the output is energized

when the light beam is not blocked (retro/thru scan), or object is present

(diffuse) the photosensor is illuminated.

Linearity (Linearity Error)-the deviation of the sensor output curve from a

specified straight line. Linearity error is usually expressed as a percent of full

scale output.

Linearity (End Point)-see Terminal Base Linearity

Linear (Output)-output that is a continuous amplified version of its input. That

is, the output is a predetermined variation of its input.

Linearity (Terminal Base)-see Terminal Base Linearity.

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Load Current-units = Amps/milliamps (DC) or Amps RMS/milliamps RMS (AC).

The maximum amount of current that a proximity sensor will switch through its

load. Load current for a particular device can be calculated by dividing the load

voltage by the load resistance. Attempting to switch a higher load current than

the sensor is rated for will result in sensor failure.

Load Impedance-the impedance presented to the output terminals of a sensor

by the associated external circuitry.

Logic-the modification of an input signal that produces delayed, pulsed, latched.

or other output response. Logic circuitry is sometimes an integral part of the

control, but more often, a separate plug-in card or module.

Low Contamination-warehouse locations, light industry applications, material

handling operations.

Low Energy Circuit-a qualitative term having no exact definition. It usually

refers to a circuit having such low voltage and current that there are no

significant thermal effects at the contact interface.

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M

Magnetic Blow-Out Switch-contains a small permanent magnet which provides

a means of switching high DC loads. The magnet deflects arc to quench it.

Maintained Contact Switch-designed for applications requiring sustained

contact after plunger has been released, but with provision for resetting.

Manufacturer's Tolerance-the maximum variation from standard allowed by

the manufacturer between products with the same catalog listing.

Make-to close or establish an electrical circuit.

Maximum Excitation-the maximum value of supply voltage or current that can

be applied to the sensor at room conditions without causing damage or

performance degradation beyond specified tolerances.

Maximum Load Current-the maximum amount of current that can flow through

a sensor and not cause sensor failure.

Measurand-a physical quantity, property or condition which is measured (e.g.,

pressure, acceleration).

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Mechanical Life-life of a switch with no (or a negligible) electrical load, and a

specified combination of actuation, environment and criterion of failure.

Mechanical life usually is limited by the life of the switch's flexing parts and

bearing surfaces.

Media compatibility-ability to operate with a specified media carrying pressure

(e.g., salt water).

Metalization-the metal pattern deposited on the sensor chip (usually outside the

diaphragm area) to permit electrical connections to be made to the chip.

Aluminum is usually used, but has potential contamination problems (known as

the "purple plague"), if not protected. MICRO SWITCH uses gold, which is

impervious to almost everything.

Migration, Contact Material-a net transfer of material from one contact to the

mating contact as a result of switching an electrical load. It usually takes the form

of a needle, cone or mound or one contact face and a corresponding pit in the

surface of the mating contact.

Minimum Life-this is an exact term only when applied to a specific group of

tested switches. It then means the lowest life figure obtained from the test of

that group of switches.

Moderate Contamination-milling operations, areas of high humidity, stream.

Modulated Light Source (MLS) Control-a photoelectric control that operates

on modulated (pulsed) infrared radiation, and responds only to that frequency

rather than steady light intensity. Modulated LED controls offer a high rejection of

troublesome ambient light.

Momentary Short Circuit Protection-output circuit protection designed to

protect the output device from damage due to a temporary (1-3 sec.) short

circuit or until an external fuse can interrupt current.

Momentary Short Circuit-a switch with contacts that return from operated

condition to normal condition when actuating force is removed. Unless otherwise

stated, all switches in this catalog are momentary.

Momentary Switch-a switch with contacts that return from operated condition

to normal condition when actuating force is removed. Unless otherwise stated, all

switches in this catalog are momentary.

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N

NEMA Ratings-National Electrical Manufacturers Association ratings of an

enclosure's ability to provide a degree of protection against contact withequipment and against specified environmental conditions.

Noise, Electrical-noise results from the presence of undesirable electrical

voltages or current. It causes devices to operate erratically (if the noise is on the

supply line to a device), or produces false information on erratic operation if

present on wires carrying signals from the output of a device to the load. Noise

can be present in the supply or picked up on lines in many ways. Pick-up from

noisy adjacent wires or metal parts is possible. Good wiring practice and/or

additional parts can be used to diminish the effects of noise.

Nominal Sensing Distance-an approximate dimension value measured from the

face of the sensor to the nearest point of the target. It does not take into

consideration manufacturer's tolerance or operational variables. Also known as

the operating point.

Non-contact-a slang expression referring to a defective condition in which a

supposedly closed switch lacks electrical continuity.

Nonincendive-inability under normal operation to ignite a hazardous mixture.

Non-modulated Controls-controls designed for indoor applications subject to

neither bright ambient light nor extreme vibration. Usually incandescent lamp

controls, scanners and light source-photoreceiver pairs.

Normal Contact Position-the normal contact position of a switch exits when no

force is applied to the plunger.

Normal High-the state of a control in which the output is high (logic1) in voltage

in the rest (Off) condition.

Normally Low-the state of a control in which the output is low (logic 0) in

voltage in the rest (Off) condition.

Normalization-process of creating sensor interchangeability.

NPN-a transistor consisting of two N-type regions separated by a P-type region.

Null-the condition when the pressure on each side of the sensing diaphragm is

equal.

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Null Offset-the electrical output present, when the pressure sensor is at null.

Null Temperature Shift-the change in null output value due to a change in

temperature.

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O

Off Delay Logic-adjustable delay (after input signal stops) before output is de-

energized.

Off State Current-the supply or bias current flowing into a solid state device

when it is in the unactuated state (see Leakage Current).

Ohm-the unit of electrical resistance. Resistance through which a current of one

ampere will flow when a voltage of one volt is applied.

On Delay Logic-adjustable delay (after onset of input signal) before output is

energized.

One-shot Logic-seepulsed logic.

Opacity-the characteristic of an object that prevents light from passing through.The opposite of translucent. Opaque objects are easy to detect since they block

light almost entirely.

Operated Contact Position-the position to which the contacts move when the

plunger is traveled to the operating point or into the overtravel range.

Operating Characteristics of a Switch-the commonly specified force, torque

and linear or angular travel properties of a switch. Examples: operating or release

force, operating point, differential, overtravel.

Operating Force-the force which must be applied to the plunger to cause the

moving contact to snap from the normal contact position to the operated contact

position.

Operating Mode-refers to the condition of the photosensor (dark or light

illuminated) that energizes output. A mode selector switch determines the

operating mode.

Operating Point-that position of the plunger at which the contacts snap from

the normal contact position to the operated contact position.

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Operating Temperature-actual range over which sensors can be operated.

Usage outside the temperature limits will result in loss of stability, change in

operate point and possible permanent damage to the sensor. Nominal sensing

distance is determined at 25 - C.

Optical Power-power or intensity of the projected light available from a

particular emitter; beam intensity.

OR Logic-an output is produced when any one or more inputs are present.

Output-the useful energy delivered by a circuit or device. Can mean energy

produced at the output terminals of an amplifier-a source of energy.

Output Impedance-the impedance across the output terminals of a sensor

presented by the sensor to the associated external circuitry.

Output Noise-the rms, peak-to-peak (as specified) AC component of a sensors

DC output in the absence of a change in input pressure.

Overpressure-the maximum specified pressure which may be applied to the

sensing element of a sensor without causing a permanent change in the output

characteristics.

Overtravel-as an operating characteristic of a switch, overtravel is the distance

through which the plunger moves when traveled from the operating point to the

full overtravel point. As a characteristic of the actuation applied to the switch,

overtravel is the distance the plunger is driven past the operating point.

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P

Parallel Circuit-a circuit in which current has two or more paths to follow. Two

electrical elements are in parallel if both terminals of both elements are

electrically connected.

Photocell-a resistive, bulk effect type of photosensor, the type used when it is

desirable to wire several photoreceivers in series or in parallel. The resistance

decreases with increasing light intensity.

Photoreceiver-a unit consisting of photosensor, focusing lens, and protective

enclosure.

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Photosensor-a light sensitive portion of a photoelectric control that converts a

light signal into an electrical signal. MICRO SWITCH uses photocells and

phototransistors.

Phototransistor-a type of photosensor. Typically used where speed of responseis important or ambient temperature variations are great.

Piezoresistance-a change in resistance in a semiconductor, caused by an

applied stress to the diaphragm.

Polarized Photoelectric Controls-controls that emit a visible LED beam and

use a special lens which filters the beam of light so that it is projected in one

plane only. The control responds only to the de-polarized reflected light from

corner-cube type reflectors (FE-RR1) or special polarized reflective tape.

PN-a diode consisting of one N-type region and one P-type region.

Pole-the number of completely separate circuits that can pass through a switch

at one time. A single pole switch can control only one circuit at a time. A double

pole switch can control two independent circuits (such as a 120 volt AC heater

and a 6 volt DC lamp) at the same time. The number of poles is completely

independent of the number of throws and number of breaks.

Polymers Between Contacts-compounds having long-chain molecular

structure, formed from simple organic contaminants on contacts, under the

influence of contact wipe and the catalytic effect of the contact material.

Power Dissipation-units = Watts/milliwatts (DC) or Volt-Amps (AC). The

amount of power that is consumed and converted to heat in normal operation.

Supply Voltage (max) x Supply Current

(max) = Power Dissipation

Volts x Amps = Watts (DC) or Volt/

Amps (AC)

Precision Snap-Acting Switch-an electromechanical switch having

predetermined and accurately controlled characteristics and having a spring

loaded quick make and break contact action.

Pressure-force applied to, or distributed over a surface expressed in terms of

force to area ratio.

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Pressure, Absolute-pressure measured relative to absolute zero pressure

(perfect vacuum). The output of the absolute sensor will change as a result of

barometric pressure change. Thus it can be used as a barometer.

Pressure, Differential-pressure between two points of measurement.

Pressure, Gage-pressure measured relative to ambient pressure. The output of

a gage pressure sensor, contrasted to an absolute pressure sensor, does not

change with a change of barometric pressure.

Pressure Range-the pressure limits over which the pressure sensor is calibrated

or specified.

Pressure, Reference-the pressure relative to which a differential sensor

measures pressure. Ambient pressure is a specific case of reference pressure.

Pressure Sensor-a device that converts an input pressure into an electrical

output.

Pressure, Static-the average pressure on the inputs of a differential pressure

sensor (sometimes referred to as common mode or working pressure).

Pretravel-the distance through which the plunger moves when traveled from the

free position to the operating point.

Proof Pressure-see Overpressure.

Proximity Sensor-a sensor with the ability to detect the presence of a metal

target, within a specified range, and without making physical contact.

Pull-Down Resistor-a resistor connected across the output of a device or circuit

to hold the output equal to or less than the zero input level. Also used to lower

output impedance of digital or analog devices. Usually connected to a negative

voltage or ground.

Pull-Up Resistor-a resistor connected across the output of a device or circuit to

hold the output voltage equal to or greater than the input transition level of a

digital device. Usually connected to the positive voltage or plus supply.

Pulse-a momentary sharp change in current, voltage, or other quantity that is

normally constant. A pulse is characterized by a rise and fall and has a finite

duration.

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Pulsed Logic-a signal modification that produces output independently of input

signal duration. Pulse duration (dwell) is usually adjustable. Also referred to as

one-shot logic. Pulsed logic may be immediate or delayed

Q

Quiescent Supply Current-the supply current being drawn when the pressure

sensor is at null.

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R

Ratiometric (Ratiometricity Error)-at a given supply voltage, sensor output is

a proportion of that supply voltage. Ratiometricity error is the change in this

proportion resulting from any change to the supply voltage. Usually expressed as

a percent of full scale output.

Range-the measurand values over which the sensor is intended to measure,

specified by the upper and lower limits.

Rectifier-a device that converts alternating current into direct current.

Reed Technology-technology where the reed contacts are designed to be

actuated by a magnet. When a magnetic field is brought close to the reed

contacts, the contacts are drawn together to make the circuit.

Reflective Scan-a scanning technique in which the light source is aimed at a

reflective surface to illuminate the photosensor. Retroreflective, specular, diffuse

scan and convergent beam are all reflective scan techniques.

Regulation %-the ratio of voltage extremes due to loading or line fluctuations.

The process of holding constant a quantity such as voltage by means of a system

that automatically corrects errors. For example, as more current is drawn from a

battery or power supply, the output voltage tends to decrease (load regulation).

With a power supply derived from AC, the DC output voltage can vary with the

variation in AC voltage (line regulation).

Release Force-the level to which force on the plunger must be reduced to allow

the contacts to snap from the operated contact position to the normal contact

position.

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Release Point-that position of the plunger at which the contacts snap from the

operated contact position to the normal contact position.

Release Travel-as an operating characteristic of a switch, release travel is the

distance through which the plunger moves when traveled from the release pointto the free position. As a characteristic of the actuation applied to the switch,

release travel is the distance the plunger is released past the release point.

Repeatability-the ability of a sensor to reproduce output readings when the

same value is applied to it consecutively in the same direction, for a specified

number of cycles, or specified time duration.

Resolution-the magnitude of output step changes as the pressure is

continuously varied over the range. This term applies primarily to potentiometric

sensors. Resolution is best specified as average and maximum resolution. Usually

expressed in percent of full scale output.

Response Time-the time it takes for a device to respond to an input signal. The

sum of thesensor, amplifier, and output response is the total response time.

Retroreflective Scan-the reflective scan technique that uses a special reflector

(retroreflector) to return light along the same path it was sent.

Reverse Polarity Protection-circuitry, usually a diode which prevents current

from flowing into the control in case of accidental mis-wiring of the plus (+) or

minus (-) terminals, preventing damage to the unit.

Ripple-the alternating component of voltage from a rectifier or generator. A slight

fluctuation in the intensity of a steady current.

Rise Time-a measure (10% to 90%) of the time required for an output voltage

to rise from a state of low voltage to a high voltage level, once a level change has

started.

Room Conditions-ambient environmental conditions under which sensors must

commonly operate, which have been established as follows:

(a) Temperature: 25 + -10 %C (77 + - 18 degrees F).

(b) Relative humidity: 90% or less.

(c) Barometric pressure: 26 to 32 inches Hg.

Note: Tolerances closer than shown are frequently specified for sensor calibration

and test environments.

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S

Saturation Voltage-the voltage drop appearing across a control device that is

fully turned On.

Scan Technique-a method of scanning objects. The two general categories are

through and reflective scan.

Self-Contained Control-a photoelectric control in which all three phases of

control - sensing, signal conditioning, and output - occur in a single device.

Self-Contained Sensor-a proximity sensor in which all three phases of control,sensing, signal conditioning, and output, occur in a single device.

Sensing Distance-the maximum recommended distance between the sensor

and standard target at which sensor will effectively and reliably detect the target.

Sensing Element-that part of a sensor which responds directly to changes in

input pressure.

Sensitivity-maximum recommended distance between the sensor and standard

target at which sensor will effectively and reliably detect the target.

Sensitivity Shift-a change in sensitivity resulting from an environmental change

such as temperature.

Sensor-a sensing element. The basic element that usually changes some physical

parameter to an electrical signal.

Series Circuit-a circuit in which current has only one path to follow.

Shielded Sensor-a sensor which "senses" only to the front of its face and

ignores metals to its side. The presence of such side metal, however, may cause a

slight shift in operating characteristics.

Signal Conditioning-to process the form or mode of a signal so as to make it

intelligible to or compatible with, a given device, including such manipulation as

pulse shaping, pulse clipping, digitizing, and linearizing.

Signal Ratio-1) broadly, the comparison of light seen by a photosensor when the

beam is blocked to the light seen when the beam is not blocked; 2) More

specifically, the comparison of photocell resistance when sensor is dark to when it

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is illuminated. Proper control application involves establishing a large dark-to-light

ratio.

Single-Pole Double-Throw (SPDT)-switch which may either make or break a

circuit, depending on how it is wired.

Single-Pole Single-Throw (SPST)-switch with only one moving and one

stationary contact. Available either normally open (N.O.) or normally closed

(N.C.).

Shock, Mechanical-a short pulse of acceleration, usually lasting only a few

milliseconds. A typical shock test pulse is a half-sine acceleration wave having

100g peak and .007 second duration.

Slide-By-the condition whereby the target approaches the sensing face of the

proximity sensor in such a direction that its center will cross the axis of the

sensing face at right angles.

Slight Contamination-indoor locations, non-industrial areas, office buildings.

Snap Action-in strict terms, snap action is a property of a switch such that the

moving contact accelerates without added travel of the plunger beyond that travel

which was required to separate the contacts. National Electrical Manufacturers

Association defines snap action as "a rapid motion of the contacts from one

position to another position, or their return. This action is relatively independent

of the rate of travel of the actuator." The word "relatively" is important. In actual

fact, the acceleration of the moving contact is partially dependent upon the

velocity of the plunger. The important point is that, once the plunger reaches the

operating or release point, the movable contact immediately transfers to its

opposite position without further travel of the plunger. A non-snap acting switch

lacks this feature.

Span-the algebraic difference between limits of the pressure range.

Specular Scan-a reflective scan technique in which reflection from a shiny

surface illuminates the photosensor, which must be precisely positioned to receive

the reflected light. The angle of incidence equals the angle of reflection.

Stability of an Operating Characteristic-the extent to which an operating

characteristic such as operating point remains constant during a specified number

of cycles of switch operation, under specified conditions of actuation, electrical

loading and environment. Most clearly expressed as a graph of the characteristic

versus cycles of switch operation.

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Standard Target-an object used for making comparative measurements of

operating distance. A square of mild steel, 1mm thick. The length of the side of

the square is equal to either:

A: the diameter of the circle inscribed on the active surface of the sensitive faceof the sensor, or

B: three times the rated operating distance, whichever is the greater.

Storage Temperature Range-the minimum and maximum specified

temperature which may be applied to the pressure sensor without causing a

permanent change in the output characteristics.

Strain Gage-a sensing device providing a change in electrical resistance

proportional to the level of applied stress.

Sublimation-the change of state of a materiel from solid to vapor and back to

solid without going through a liquid state.

Supply Current-units = Amps or milliamps. The amount of current necessary to

maintain operation of a photoelectric control, proximity sensor or control base.

Sometimes referred to as Current Consumption.

Supply Voltage-units + Volts. The range of power required to maintain proper

operation of a photoelectric control, proximity sensor or control base. The

difference in potential (or range of difference in potential) necessary to operate

the unit.

Switching Frequency-the actual number of targets to which the sensor can

respond in a given time period, usually expressed as Hertz (cycles per second).

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T

Target-the part or piece being detected.

Terminal Base Linearity-T.B.L. (End Point Linearity) - a method of defining

linearity. The maximum deviation of any data point on a sensor output curve from

a straight line drawn between the end data points on that output curve. (T.B.L. is

approximately twice the magnitude of B.F.S.L.).

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Terminal Line-a theoretical slope for which the theoretical end points are

normalized at 0 and 100% of both measurand and output. Interchangeability

error is referenced to this line.

Temperature Error-the maximum change in output, at any input pressurewithin the specified range, resulting from a change in temperature.

Thermal Drift Chart-a chart illustrating sensor operating variance due to

changes in temperature.

Thick-Film-technology using silk screened pastes to form conductor, resistor,

themistors, and insulator patterns; screened onto the substrate (usually ceramic)

and cured by firing at elevated temperatures.

Thin Film-a technology using vacuum deposition of conductors and dielectric

materials onto a substrate (frequently silicon) to form an electrical circuit.

Threshold Response-a control type that responds to the change in input signal

level. Plug-in amplifiers are either threshold or transition responsive.

Throw-the number of circuits that each individual pole of a switch can control.

The number of throws is completely independent of the number of poles and

number of breaks. A single-pole double-throw single-break switch connects the

common terminal of the switch to the normally closed terminal when the plunger

is free, but connects the common terminal to the normally open terminal when

the plunger is depressed. A single-pole single-throw single-break switch has a

common terminal and either a normally open terminal or a normally closed

terminal but not both.

Thru Scan-a scanning technique in which the emitter (light source) is aimed

directly at the receiver. Also called direct scan and transmitted scan, since light is

transmitted directly, not reflected to the sensor. Presently, it is the only scanning

technique commonly used to scan distances greater than 40 feet.

Time Delay Before Availability-also know as False Pulse Protection. Outputs

are turned Off when power is first applied during this time period.

Total Travel-the distance from the plunger free position to the full overtravel

point.

Transducer-a fully packaged, signal conditioned, compensated and calibrated

sensor.

Transient Protection-circuitry to guard against spikes induced on the supplylines by inductive sources such as heavy motors or solenoids turning On and Off.

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Transients-in electronic usage, usually refers to an unwanted, temporary, large

increase or decrease in a current or supply voltage that only occurs occasionally.

Almost always due to reactive components during rapid changes in voltage or

current.

Transition Responsive-a control type that responds to the rate of change in

light intensity rather than the level change. Used to detect fast moving objects

that cause little change in light intensity level.

Translucent-allows light to pass through. Detecting translucent objects is often

best done with retroreflective scan, during which the light must pass through the

object twice, thereby causing more of a signal change (larger signal ratio).

Transmitter-a transducer with a current loop output, typically 4 to 20 mA,

enabling transmission of a signal over a longer distance.

TTL-a generic term for Transistor Logic which is used extensively in digital

electronics systems.

TTL Compatibility-TTL (transistor-transistor-logic) requires NPN (current

sinking) input signals. Reliable operation demands maximum input sensor voltage

drop of 0.8 V. Most TTL compatible interface devices have voltage drops of less

than 0.7V.

Typical-(as used herein): refers to the target value or where a range is given,

represents an estimate of where 2/3 of the total population of several production

runs would be.

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U

UL-Underwriter's Laboratories, Inc., a non-profit organization that establishes,

maintains and operates laboratories for the examination and testing of devices,

systems and materials primarily for safety.

Unidirectional Differential Pressure Sensor-a differential pressure sensor

requiring the greater input pressure to be applied to a specified pressure port.

Unshielded Sensor-a sensor with limited side and front sensing capabilities.

Usable Sensing Distance-sensing distance after temperature range tolerance

and manufacturers tolerance are taken into account.

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V

Velocity-the rate at which the position of a moving object is changing. Velocity

has two characteristics: magnitude (speed) and direction.

Voltage-units = Volts (DC) or Volts RMS (AC). The term used to designate the

electrical energy, differential that exists between two points and is capable of

producing the flow of current when a closed path is connected between the two

points.

Voltage Drop-units = Volts (DC) or Volts RMS (AC). Sometimes referred to as

Saturation Voltage. In any solid state control that switches a load, there will be

some voltage dropped across the output. This voltage drop or saturation voltage

will often vary with the amount of current going through the output section and

the load. It should be specified with current conditions.

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W

Welding, Contact-one of several conditions that may cause switch contacts to

fail to separate at the intended point of plunger travel. As the name implies, the

contacts literally are welded together as a result of the electrical and thermal

effects at the contact interface.

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X

Y

Z