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PRINCIPLES OF PRESSURE MEASUREMENTPrepared by : Sakinah
AnsaryAssisted by : Ahmad NizarReviewed by : Ezatolah MardasiDate :
11th of March 2004
Instrument & Control Department
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TPCP Descriptor
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INSTALLATION CONSIDERATIONMAINTENANCE & CALIBRATIONDEVICE
SELECTIONREFERENCESVariable Inductance Pressure SensorVariable
Differential Transformer TransducerVariable Capacitance
TransducerPotentiometric TransducerBourdon Tube
Bellows Sensor
Diaphragm Sensor
DATASHEETSStrain GaugeMECHANICAL PRESSURE ELEMENTELECTRICAL
PRESSURE ELEMENTELECTRONIC PRESSURE ELEMENTBASIC PRINCIPLES
PRESSURE MEASUREMENT
Pressure TransmitterPressure GaugeResonant Wire Pressure
TransducerOptical Pressure TransducerPiezoelectric
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BASIC PRINCIPLES
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What is PRESSURE??Pressure is Force exerted over a unit Area
P = F / A Where P = Pressure F = Force A = Area
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UNITS of PressurePounds per square inch (PSI)Newton force per
square meter / Pascal (Pa); where kPa is commonly usedKilogram per
square centimeter (kg/cm2)Inch of water (inH2O)Millimeter of water
(mmH2O)Inch of mercury (inHg)Millimeter of mercury / torr
(mmHg)Atmosphere (atm)Bar
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Conversion of common UNITS of Pressure
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Absolute & Gauge PressureAbsolute Pressure; denoted as a: -
Measured with reference to ZERO pressure, eg. psia
Gauge Pressure; denoted as g: - Measured with reference to
ATMOSPHERIC pressure, eg. psig
Thus, Pressureabsolute = Pressuregauge + Pressureatm
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PTPressure AppliedHLDiaphragmAtmosphericPlugged but not
sealedReference pressureGauge PressurePTPressure
AppliedHLDiaphragmVacuumedPlugged and sealedReference
pressureAbsolute Pressure
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Differential PressureDifference in pressure measurements taken
at TWO related points; denoted as d, eg. psid P = Phigh Plow
Vacuum
Measured BELOW atmospheric pressure
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Comparison of Pressure Modes
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Pascalss LawStates that whenever an external pressure is applied
to any confined fluid at rest, the pressure is increased at every
point in the fluid by the amount of the that pressure
Application of Pascals Law: Hydraulic presses, jacks or breaks
Instruments used for measurement and calibration
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MECHANICAL PRESSURE ELEMENTS
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Mechanical Pressure ElementsBase on pressure acting on a surface
area inside the element to provide a force that causes a mechanical
deflection
Common elements used are: - Bourdon tubes - Bellows elements -
Diaphragms
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Bourdon Tubes ElementsMost common type of pressure sensor
Increased pressure causes the flattened cross-section to
straighten and move the closed end
Closed end is attached to mechanical linkage
Linkage is connected to a pointer or other output device
There are three types of forms: - C-Tube - Spiral - Helical
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C-Tube (Low:015 psig & High:0-10000 psig)Most commonly used
element
Simple and lease expensive to manufacture
Bulky and subject to damage from over pressuring
Two bourdon tubes are used to measure differential pressure; (P1
P2)
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Spiral (Low:0-10 psig & High:0-10000 psig) Helical (Low:0200
psig & High:0-6000 psig)Much longer than C-Tube and is coiled
into a spiral and helix respectively
More costly to manufacture
Occupies less space for given amount of movement
Multiple turns allow thicker material for a given sensitivity;
less chance to damage
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Bellows SensorsAxially flexible, cylindrical enclosure with
folded sides [A]
Increased pressure causes the closed end to extend axially
Movement rotates a pointer or actuates a controller or
transmitter by mechanical linkage [B]
Movement of the bellows is opposed by - Spring action of the
bellows material - Pressure surrounding the bellows - External
force by spring [C] or another bellow [D]
Accurately measures LOW pressure compared to Bourdon tubes as
well as Vacuum and differential pressure [E] - Absolute ranges : 0
100 mmHg - Gauge ranges : 0 5 inH20
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Bellows Sensors[A][D][C][B][E]
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Diaphragm SensorsUsed to detect slight changes in pressure
Axially flexible, thin, flat and corrugated disk held in
place
Increase pressure on one side causes the other side to
deflect
Force opposing the pressure is the sum of: - Spring constant of
the diaphragm - Pressure on the opposite side of the diaphragm -
Spring constant of opposing spring
Axial movement can measure liquid level, rotate a pointer or
activate a controller by attaching the free end to linkage [A]
There two types of elements: - Elastic element - Limp
element
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Elastic ElementUsually metallic - Single; either flat or
concentric corrugations [B] - Capsular; consists of two diaphragms
welded together at their perimeter [C]
Limp Element
Metallic or non-metallic - Does not give an opposing force to an
applied pressure - Single diaphragm form - Used to contain pressure
and exert a force on an opposing spring [D]
Able to measure VERY LOW pressure
Common to measure absolute/gauge pressure down to 0 0.2
inH2O
Does not provide much movement which limits their use in gauges
and controllers
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Diaphragm Sensors[A][B][D][C][E]
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ELECTRICAL PRESSURE ELEMENTS
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Electrical Pressure ElementsElectro-mechanical pressure
transducers convert the motion produced by mechanical sensing
elements into changes in electrical signals for monitoring and
controlling process pressure
Generally, the electrical output is directly proportional to the
applied pressure
Types of electrical pressure elements are: - Potentiometric
transducer - Variable Capacitance Transducer - Variable
Differential Transformer Transducer - Variable Inductance Pressure
Sensor
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Potentiometric TransducerUtilizes a Wheatstone bridge circuit in
which one of the bridge resistors is replaced by a
potentiometer
Potentiometer is a wire-wound resistor with a movable slide on
it
When the slide moves, the resistance value of the potentiometer
changes which changes the resistance in the bridge circuit
But, this transducer has a limited response to pressure changes
and can easily wear and damage the windings
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Potentiometric Transducer
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Variable Capacitance TransducerConsists of two metal plates; one
of which is linked to a movable mechanical pressure element ie.
diaphragm and the other is a static plate
Both plates are separated from each other by dielectric
material
When distance between plates changes, capacitance changes
resulting in changes in opposition to current flow in the AC
circuit
Thus, by measuring the current flow, changes in pressure can be
detected
Ideal for measuring low input levels
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Advantages:- Low hysteresis- Good linearity, stability and
repeatability- Fast response Disadvantages:- High impedance output-
Complex electronics
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Linear Variable Differential Transformer (LVDT) TransducerLVDT
operates on the inductance ratio principleThree coils are wired
onto an insulating tube containing an iron core, which is
positioned within the tube by the pressure sensorAlternating
current is applied to the primary coil in the center, and if the
core also is centered, equal voltages will be induced in the
secondary coilsBecause the coils are wired in series, this
condition will result in a zero outputAs the process pressure
changes and the core moves, the differential in the voltages
induced in the secondary coils is proportional to the pressure
causing the movement
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LVDT-type pressure are available with ranges 0 - 30 psig to 0 -
10000 psigIt can detect absolute, gauge or differential
pressures
Advantages:- Rugged; will not be easily damaged- Do not need to
compensate for friction; movable core not in touch
Disadvantage:- Susceptible to mechanical wear and sensitivity to
vibration and magnetic
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Variable Inductance Pressure SensorTwo coils are wired in
opposition to form two legs of an AC circuit
A diaphragm made of a magnetic material is placed between the
two coils
Pressure form the measured process is applied to one side of
diaphragm while the other side is exposed to a reference pressure
ie. atmospheric pressure
Changes in process pressure will cause the diaphragm to flex and
move towards one of the coils and away from the other
As the diaphragm moves, the relative inductance of the coils
changes which change the circuit output, thus can be measured as
pressure
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Advantages:- Rugged and stable in performance- High output and
dependable overload protection
Disadvantages:- Frequency response is limited- No linear output
at times
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ELECTRONICS PRESSURE ELEMENTS
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Strain GaugeThere two types of strain gauges: - Bonded Strain
Gauges - Unbonded Strain Gauges
Bonded Strain Gauges
Discrete metal/silicon foil bonded or glued to a piece of
insulating material (usually some movable part of a mechanical
pressure sensing element eg. diaphragm) that will bend or flex with
pressure changes
As an active sensing element strains or bends, the bonded foil
will be strained
The tension of the foil will change its resistance
Ideal for taking dynamic measurements
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Advantages:- Fast response- Low source impedance- Minimum
mechanical motion, size and weight- Works well with AC and DC
power
Disadvantages: Loss of accuracy due to hysteresis Costly output
measurement devices
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Unbonded Strain GaugesConsists of insulated posts that support
stretched small wires that will respond to changes in pressure
These posts are linked to a mechanical pressure element eg.
diaphragm which deforms under pressure
The resulting changes in tension in the wire will change the
resistance indicating changes in process pressure
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Advantages:- High sensitivity- Moderate accuracy- May be used in
high temperature; no adhesive required
Disadvantages:Frequent recalibration due to hysteresisZero tends
to shift; long term changes in wire resistivity and stress
relief
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Resonant Wire Pressure TransducerIn the design, a wire is
gripped by a static member at one end, and by the sensing diaphragm
at the other
An oscillator circuit causes the wire to oscillate at its
resonant frequency
A change in process pressure, changes the wire tension, which in
turn changes the resonant frequency of the wire
A digital counter circuit detects the shift
Because this change in the frequency can be detected quite
precisely, this type of transducer can be used for low differential
pressure applications as well as to detect absolute and gauge
pressures
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Advantage:- It generates inherently digital signal; can be sent
to a stable crystal clock in microprocessor
Disadvantages:- Sensitive to temperature, shock and vibration
variation- Nonlinear output signal
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Optical Pressure TransducerAn LED is used as light source and a
vane which blocks some of the light as it is moved by a
diaphragm
As process pressure changes the vane between light source and
measuring diode, amount of IR received changes as compared to
reference diode which is never blocked by the vane
Detects the effects of minute motions due to changes in process
pressure and generate a corresponding electronic output signal
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Advantages:- Immune to temperature effects because all diodes
are effected equally by changes in temperature- Hysteresis and
repeatability errors are nearly zero due to small movements (<
0.5 mm)- Low maintenance- Stable and designed for long duration
measurements
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PiezoelectricWhen pressure, force or acceleration is applied to
a quartz crystal, a charge is developed across the crystal that is
proportional to the force applied.The fundamental difference
between these crystal sensors and static-force devices such as
strain gages is that the electric signal generated by the crystal
decays rapidly.This characteristic makes these sensors unsuitable
for the measurement of static force or pressures but useful for
dynamic measurements.Pieoelectric device can further be classified
according to whether the crystal's electrostatic charge, its
resistivity, or its resonant frequency electrostatic charge is
measured.Depending which phenomenon is used, the crystal sensor can
be called electrostatic, piezoresistive or resonant.The desirable
features of peizoelectric sensor include their rugged construction,
small size, high speed, and self-generated signal.Piezoelectrics
are sensitive to temperature variations and require special cabling
and amplification.
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Piezoelectric (Working Principle)When pressure is applied to a
crystal, it is elastically deformed.This deformation results in a
flow of electric charge (which lasts for a period of a few
seconds).The resulting electric signal can be measured as an
indication of the pressure which was applied to the crystal.This
sensor cannot detect static pressures, but are used to measure
rapidly changing pressures resulting from blasts, explosions,
pressure pulsations or other sources of shock or vibration.
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INSTALLATION CONSIDERATIONS
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Installation ConsiderationsManner in which a pressure measuring
instrument is installed is an important factor in achieving
accurate and reliable operation
Measuring device is normally placed in direct contact with the
process and should be installed in visible and readily accessible
locations
In some applications, it is desirable to prevent the process
fluid from coming in contact with the sensing element
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The process fluid may be noxious, poisonous, corrosive,
abrasive, freeze or decompose at ambient temperature or
hotter/colder than the sensor can tolerate
Other reasons are to filter out potentially plugging solids or
to remove potentially damaging pressure spikes or vibrations
Special installation precautions must be taken to protect the
measuring instrument and reading accuracy
Some of the protection devices used include: - Seal pots -
Mechanical pressure seals - Chemical seals - Pulsation dampeners -
Snubber
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Seal PotsUsed when measuring steam pressure or in processes in
which a vapor will condense into liquid at ambient temperature
Acts as a condensate chamber and provides a large area of liquid
contact between process and measuring instrument
Lead lines to the measuring instrument should be full of liquid
to protect the instrument from high temperatures
In some cases, the seal pot, line and instrument are filled with
a sealing fluid to prevent freezing
When a sealing fluid is used, the measuring instrument should be
zeroed with the lines full of the seal fluid; wet leg
installation
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Seal Pots
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Mechanical Pressure SealsInstalled between the measuring
instrument and the process
Isolates the instrument from corrosive, toxic or plugging
effects of the process
Operation is based on Pascals Law; force applied to a liquid in
a confined area is transmitted undiminished throughout the
liquid
Designed so that process pressure exerts a force on the
diaphragm, which is transferred via the fill liquid to the
measuring instrument
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Mechanical Pressure SealsType of fill liquid used will depend on
the particular application
In all cases, the liquid should have a: - Low freezing point-
High boiling point- Low viscosity- Low coefficient of thermal
expansion
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SiphonSiphon or pig tail is a type of mechanical seal commonly
used
Used to protect pressure gases from thermal shock in high
process temperatures
Steam and other vapors condense and form a liquid trap in the
lower portion of the siphon
Usually mounted vertically to prevent thermal shock
When mounted horizontally, siphon will absorb some mechanical
shock and vibration
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Chemical SealsChemical seals is also known as a diaphragm
protector which uses diaphragm seals
Designed for use where the process fluid being measured would
normally clog the pressure system or might freeze due to changes in
ambient temperature and to withstand corrosive effects of certain
process fluids
The diaphragm seals the pressure system from process fluid
Any movement of the diaphragm will change the process pressure
accordingly and indicated by the gauge pointer
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Pulsation DampenersUsed in applications where there is rapid
fluctuation of process pressure
Sudden changes in pressure make it difficult to read the actual
value of the pressure measurement and will cause unnecessary damage
on the measuring instrument
Fluctuations can be minimized by placing a restriction in the
impulse line to reduce the response rate of the instrument
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Pulsation DampenersAvailable in a variety designs:- Contains a
porous filter disc at the inlet to the restriction; rate of
response is delayed by a fixed time of about 10 seconds [A]-
Contains a piston that absorbs shock and surge by rising and
falling with pressure impulses [B]- Design provide a means for
adjusting the amount of restriction to obtain the best damped
response [C&D]
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SnubberPressure snubber has the following functions:
- Eliminates pressure instrument failure due to hydraulic or
pneumatic shock- Smoothes out pressure impulses and fluctuations-
Removes harmful solids from actuating fluid- Assures steady average
pressure readings
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Throttling ScrewSimplest means of providing a restriction in the
socket
This device is threaded into a tapped hole
Its size is selected base on the viscosity of the pressure
fluid, rapidity of pressure fluctuations and the amount of
dampening effect desired
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Pressure Tap for GasFor non-condensing gasses, tapping point
should be made to the side or upper quadrant of the process line
and fitted with a suitable process isolation valve
The pressure transducer (transmitter) should be positioned above
the tapping point with its process connection downwards to allow
any condensate that may form to drain back into the process without
blocking the impulse line
To ease service and commissioning the transducer should be
fitted with an isolation valve and vent (or vent valve
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Pressure Tap for Vapor/SteamFor vapor or steam service, the
tapping point should be made to the side or upper quadrant of the
process line and fitted with a suitable process isolation valve
The pressure transducer (transmitter) should be positioned below
the tapping point so that the impulse line will stay filled with
condensate in service
The distance below the impulse line should be chosen to ensure
that adequate cooling occurs to prevent thermal damage to the
transducer
For steam service the impulse line must be filled with water
prior to startup to prevent possible thermal damage to the
transducer by live steam
To ease service and commissioning the transducer should be
fitted with an isolation valve and vent (or vent valve)
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Pressure Tap for LiquidFor liquids, the tapping point should be
made to the side or lower quadrant of the process line and fitted
with a suitable process isolation valve. If sediments may be
present, do not fit to the bottom of the process lineThe pressure
transducer (transmitter) should be positioned below the tapping
point with its process connection upwards (if possible) to allow
any gasses that may form to vent back into the processTo ease
service and commissioning the transducer should be fitted with an
isolation valve and vent (or vent valve)
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MAINTENANCE& CALIBRATION
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MaintenancePressure sensors require scheduled, periodic
maintenance and/or recalibrationIt is necessary to periodically
remove the transducer from the process and to make sure that this
procedure does not require shutting down the process and does not
cause injury or damageBecause the process fluid may be toxic,
corrosive, or otherwise noxious to personnel or the environment, it
is necessary to protect against the release of such fluids during
maintenanceA three-way manifold can provide such protection. In the
illustration,
- Valve P is used to isolate the process - Valve D serves to
discharge the trapped process fluid from the instrument into some
safe containment- Valve T is to allow the application of a known
calibration or test pressure to the instrument
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CalibrationThe dead weight tester is generally regarded as the
most accurate method in calibration of pressure instruments
It is used for calibration of pressure gauges, transmitters,
transducers, etc.
When fluid pressure generated by a screw pump acts on the bottom
of a vertically free floating piston, the force produced pushes the
loaded free piston vertically upwards
The piston floats freely in its cylinder and the pressure in the
circuit will be determined by the weights loaded on the piston
divided by the effective area of the piston with corrections for
value of acceleration due to gravity, air buoyancy and surface
tension
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Dead-Weight Tester
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DEVICE SELECTION
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Electrical/Electronics Pressure Element SelectionFigure below
shows the selection of various electrical/electronic pressure
elements at a certain pressure
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Pressure Transmitter SelectionPressure transmitter is used where
indication, monitoring and/or controlling of pressure is required
at a location not adjacent to the primary elements eg. panel or
control room
The pressure range selection is made base on:- Process data
given by process engineers - Referring to Line List- Obtained from
Heat and Material Balance
There are two types of transmitters: - Pneumatic: 3-15 psig -
Electronic: 4-20 mA
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Pneumatic TransmitterThe differential pressure to be measured is
applied across a pair of metal diaphragms welded to opposite sides
of a capsule
Space between the diaphragms and core member is filled with
liquid
The force developed on the diaphragm by differential pressure is
brought out of the transmitters by a rigid rod passing through a
metal seal diaphragm
This force is opposed by a balancing force developed by
pneumatic bellows
Imbalance between capsule force and pneumatic bellows force is
sensed by a pneumatic nozzle-baffle; which in turn a servomechanism
responsive to nozzle pressure re-establishes the balance
As a result, pneumatic pressure is maintained exactly
proportional to differential pressure and is used as output
signal
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Pneumatic TransmitterElectronic Transmitter(Rosemount)
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Electronic TransmitterThis particular type utilizes a 2-wire
capacitance technique
Process pressure is transmitted through isolating diaphragms and
silicone oil fill fluid to a sensing diaphragm in the center of the
cell
The sensing diaphragm is a stretched spring element that
deflects in response to differential pressure across it The
displacement of the sensing diaphragm is proportional to the
differential pressure
The position of the sensing diaphragm is detected by capacitor
plates on both sides of the sensing diaphragm
The differential capacitance between the sensing diaphragm and
the capacitor plates is converted electronically to a 420 mA
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The operating range, maximum and minimum pressure should be
considered
Gauge pressure transmitters should have an overpressure rating
of at least 150% of the maximum rating operating pressure
Parameters used in transmitters:- Span: actual pressure range to
be measured after the transmitter adjustment- Range: pressure range
within which the span can be adjusted
Most transmitters have two adjustments- Zero: output minimum is
adjusted as 4 mA, 3 psig or 20 kPa at zero pressure- Span: output
maximum is adjusted as 20 mA, 15 psig or 100 kPa when pressure as
at top of the span
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(Rosemount)
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(Rosemount)(Foxboro)Functional Overview Block Diagram for
Pressure Transmitter
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Pressure Transmitter Sensor Units(Rosemount)The sensor is
isolated mechanically, electronically and thermally from the
process medium and the external environmentMechanical and thermal
isolation is achieved by moving the sensor cell away from the
process flange to a position in the neck of the electronics
housingThis design relieves mechanical tress on the cell, thereby
improving static pressure performance and removes the sensor from
direct process heatGlass-sealed pressure transport tubes and
insulated cell mountings provide electrical isolation, and thus
improve electronic circuitry's flexibility, performance and
transient protection
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Capacitance Principle (1967)The pressure applied to the
transmitter high and low pressure sides is transmitted by a sealed
fill-fluid to both sides of a sensing diaphragmAs the applied
differential pressure causes the sensing diaphragm to move, the
capacitor of the cell changes as the pressure changesThe amplifier
unit converts the change in capacitance to a 4 to 20 mA signalThe
sensing diaphragm is a stretched spring element that deflects in
response to differential pressure across itThe maximum sensing
diaphragm movement is 0.1mmA 1m distortion of a sensing diaphragm
is equivalent to a 1% error
(Yokogawa)
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Piezoresisitive Principle : (1982) The solid state sensor
consists of a Wheatstone Bridge circuit which has resistors
diffused into a silicon chip, thereby becoming a part of the
automatic structure of the silicon
As pressure is applied to the IC chip diaphragm, strain is
created in the bridge resistors
Piezoresistive effects created by this strain, change the
resistance in the arms of the bridge, producing a voltage
proportional to pressure
Output from the bridge is typically in the range of 75 to 150mV
at full scale pressure for a bridge excitation 1.0 mA
(Yokogawa)
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Single Crystal Silicon Resonant Principle : (1992)In the single
resonant sensor principle, the sensor has two H-shape resonators on
a diaphragm chip, one in the center of the chip and the other is
located slightly off to the sideThe resonating element consists of
a silicon beam, which is deflected by the application of pressureAs
pressure is applied, the center resonator goes into compression,
and the outer resonator goes into tension altering its natural
frequencyThe output of the compression resonator increases from 90
to 110 kHz and the output of the tension resonator decreases from
90 to 70 kHzThis produces a high differential output directly
proportional to the pressure being appliedThe digital frequency is
easily managed by the CPU as a time based function (Yokogawa)
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SENSOR COMPARISION
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Transmitter SelectionConsiderations that should be viewed when
selecting a pressure transmitter:
i. Functional Specification- Temperature; process, range-
Pressure; operating and min/max- Environment; humidity- Hazardous
Location; Zone, Group, Ex-Proof, IS- Damping; time constant and
corner frequency- Output; range and no of wire- Zero Elevation or
Suppression- Power Supply and Load Limits
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ii. Performance Specification- Accuracy- Linearity- Hysteresis-
Repeatability- Temperature Effect- Overpressure Effect- Static
Pressure Effect- Vibration Effect- Power Supply Effect- Load
Effect
iii. Material
iv. Feature
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Pressure Gauge Selection(Ashcroft)
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Pressure Gauge SelectionType of Pressure Element Bourdon,
Bellows or DiaphragmType of Gauge Gauge Pressure, Absolute
Pressure, Differential Pressure, Compound Pressure Pressure Range
and Unit operating pressure bet. 50-75% of scaleDial Size - 2 1/2
up to 12; 4 (commonly used)Mounting - Bottom, Lower/Center Back or
FlushPressure Element Material Stainless Steel, MonelCase Material
Phenolic, Stainless SteelLiquid Filled eg. siliconAccessory -
Pulsation Dampener, Snubber, Throttle Screw, Siphon or Diaphragm
SealBlow Out Vent A feature which relieves pressure in the gauge
caseConnection Size 1/2 or 1/4 NPT
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Types of Mounting(Swagelok & Ashcroft)
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DATASHEET SAMPLES
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ADDITIONALINFORMATIONTEMPERATURE COMPENSATION ON PRESSURE
TRANSMITTER
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TEMPERATURE COMPENSATION ON PRESSURE TRANSMITTERThe sensor of
the smart transmitter is uniquely temperature compensated to ensure
high performanceAfter the basic transmitter has been assembled, it
is tested throughout its input pressure range at various ambient
temperatureData from these tests are translated into compensation
coefficients and entered into a memory chip (EEPROM) in the sensor
assembly to provide precise temperature error compensation during
transmitter operationThe coefficients make the transmitter accurate
with changes in pressure and changes in ambient temperatureThis
compensation is proposed because temperature changes will cause the
pressure element to expend or contractAs a result instability of
output will occur
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REFERENCESBasic Instrumentation 3rd Edition Chapter 5: Pressure
Measurement and ControlSKG 14: Pressure, Flow, Level and
Temperature Training ModuleYokogawa BrainWave NewsletterRosemount
Measurement Model 3051 Smart Pressure Transmitter Family
BrochureFoxboro Intelligent Pressure Transmitter Product
SpecificationAshcroft Pressure Gauges Product CataloguesSwagelok
Pressure Gauge Technical BrochureEndress and Hauser Industrial
Automation 2003 Product Catalogue www.sciencemadesimple.net
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Thank You
Hope that this presentation will help you take the PRESSURE off
yourself and put it on the right SENSOR for your application