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Fundamentals of Industrial Control WEEK 3. This week : Pressure Measurement Terminology Pressure Sensor Technology . How was it last Week?. Recap of last Week: Remember the terms? Types of Level sensors Did we miss any? Homework done?!. What are Sensors?. Sensors:

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Fundamentals of Industrial Control WEEK 3

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fundamentals of industrial control week 3

Fundamentals of Industrial Control WEEK 3

This week : Pressure Measurement


Pressure Sensor Technology

how was it last week
How was it last Week?

Recap of last Week:

Remember the terms?

Types of Level sensors

Did we miss any?

Homework done?!

what are sensors
What are Sensors?


Primary Role: Collecting and Sending Data

about a measured variable

Displaying /Recording

Comparing data to what is to what it should be

Allows us to make decisions

  • A device that tranforms one form of energy to another
  • can be mechanical/electrical/hydraulic or combination of both
  • output : make it more meaningful to user
  • RANGE:Min/Max design in normal operation
  • Zero:Where the measurment starts
  • Zero Drift:When the signal varies from its initial setting.
  • Short Term Drift:Error expected immediately
  • Long Term Drift: Aging of components in which we have no control over
  • Sensitivity:The amount of sensor output change with respect the amount of input signal applied.
  • Resolution: The smallest amount of change in input that can be seen by a sensor.
  • Response: The time it takes to sense a change in input before it changes the output
  • Linearity:A sensor s function to have an output in a linear relationship to its output.
  • BSL: Best Straight Line method
  • Examples on non linear sensors
  • Hysteresis:Sensors Reaction to the rise and fall of its initial input vs. its output reaction to input change.
confusion 101
Confusion 101:
  • Accuracy=closeness of the true value of the variable being measured.
  • Precision=reproducibility of doing it over and over again.
pressure measurement
Pressure Measurement
  • Pressure can be created either compression( pumping)
  • Or Expansion in a closed vessel
  • Or by Gravitational exertion in a vessel
force exerted by liquids
Force Exerted By Liquids
  • In a vessel , force exerted on the walls of the vessel have three contributing factors:
  • Height of the liquid
  • Specific gravity of the Liquid
  • Temperature of the liquid
same idea but on a closed vessel
Same idea but on a closed vessel
  • Pressure will increase in a vessel if the temperature increases which causes expansion
gas laws
Gas Laws:
  • Boyles Law: P1V1=P2V2 works as long as temperature is kept constant
  • Charles Law:V1/T1=V2/T2 works as long as pressure is kept constant
  • Idela Gas law: P1V1/T1=P2V2/T2 works on the day to day applications!
pressure measurement1
Pressure Measurement
  • Law Class 101 is now finished for the Day...
pressure measurment basics
Pressure Measurment Basics
  • Manometers: U tube and Inclined designs
  • Great for low pressures
  • Still used for low pressure <10 psi applications
u tubes

27.8” of H2O=1 PSI

U -Tubes

No. 246 solid plastic inclined style stationary gage with 0-6" w.c. range.

u tubes using mercury
U- tubes using Mercury
  • Well type manometers are easiest to read
  • ± 1/2 of the smallest graduation accuracy
  • Full scale verniers available for best resolution
  • Measure differential, vacuum or gauge pressure
  • SWP = 250 PSI or optional 500 PSI

Used for Vacuum reference principally

30.65 inches of mercury = 1 Atmosphere

=14.7 psi

g and a psig vs psia
G and A PSIG vs PSIA

Pounds per square inch Gauge

= reference to atmosphere on earth

Pounds per square inch Absolute

= Reference to “Space Vacuum”

PSIG= PSIA+ 14.7

types of primary sensors
Types Of Primary Sensors
  • Elastic Deformation(means they move with very little pressure)
  • Diaphragm type
  • Metallic and Non Metalic
  • Primary use is Low Pressure
  • 10 Psig and under
  • Typical is inches W.C. and 0-5 psig

Diaprhragm Gauges P42

Diaphragm elements are circular-shaped, convoluted membranes. They are either clamped around the rim between two flanges or welded and subject to the pressure of the media acting on one side. The deflection caused in this way is used as a measurement for the pressure and is indicated by a pointer. Compared with bourdon tubes, these diaphragm elements have a relatively high activating force and because of the circular clamping of the element they are insensitive to vibration. The diaphragm element can be subjected to higher overload through load take-up points (by bringing the diaphragm element against the upper flange). Moreover, the pressure gauge can also be protected against extremely corrosive media by coating with special material or covering with foil.Wide connection ports, open connection flanges and purging plugs can be integrated for measuring highly viscous, impure or crystallizing media. Pressure ranges are between 0...16 mbar and 0...40 bar in accuracy class 0.6 to 2.5.

bourdon types
Bourdon Types
  • P43 deflection of solid Tube

Bourdon tubes are circular-shaped tubes with an oval cross-section. The pressure of the media acts on the inside of this tube which results in the oval cross section becoming almost round. Because of the curvature of the tube ring, the bourdon tube bends when tension occurs. The end of the tube, which is not fixed, moves, thus being a measurement for the pressure. This movement is indicated by a pointer. Bourdon tubes bent at an angle of approx. 250° are used for pressures up to approx. 60 bar.

For higher pressure, bourdon tubes are used which have a number of superimposed coils of the same diameter (i.e. helical coils) or helical-shaped coils (i.e. helical springs) at one level. Bourdon tubes can only be protected against overload to a limited extent. For particularly difficult measuring operations, the Wika pressure gauge can be provided with a chemical seal as a separation or protection system.

The pressure ranges are between 0...0.6 and 0...4000 bar with a reading accuracy (or accuracy class) from 0.1 to 4.0%.

spiral type
Spiral Type
  • P44
  • Same idea as bourdon except very expensive to make and lower pressure capabiltiy
  • Also known as a helical element
when to use what
When to use what!!??
  • From 0-10 PSI use Diaphragm
  • Bellows elements are low pressure as well but are no longer used in gauges
  • From 5-30 psi Helicals are offered but are not price practical.
  • 15 psi and higher Bourdon tubes are the clear choice.

Dual Scale


Inner ScaleOuter Scale

Inner ScaleOuter ScaleFigure IntervalsMinor Grad.Figure IntervalsMinor Grad.

0/9 oz./in.2 0/15 in. H2O 1 0.2 5 0.2

0/20 oz./in.2 0/35 in. H2O 5 0.5 5 0.5

0/35 oz./in.2 0/60 in. H2O 5 0.5 10 1

0/60 oz./in.2 0/100 in. H2O 10 1 10 1


Standard Ranges


Type number1008A/AL

Size63mm (2.5"), 100mm (4")

Case304 stainless steel, dry (1008A), or liquid filled (1008AL)

Fill fluidGlycerin

Ring304 stainless steel, crimped


DialBlack figures on white background, aluminum

PointerBlack, aluminum

Bourdon tube"C" shaped bronze (vac.-600 psi and compound) Helical bronze (1000 psi-6000 psi) Helical stainless steel (10,000 psi-15,000 psi)

MovementPatented PowerFlexTM with polyester segment

SocketBrass, with O-ring case seal

RestrictorBrass throttle plug 0.013" orifice in all ranges (except vacuum and 15# psi ranges)

Connection.25 NPT lower and back

RangesVac. thru 15,000 psi and compound. Equivalent metric ranges available

AccuracyASME B40.1, Grade B, 3-2-3

Operating temperatureDry gauge: -40° F to 150° F Glycerine filled: 20° F to 150° F Silicon filled: -40° F to 150° F

Gauge Options

CaseSealed case, field-fillable (LJ) Silicone filled (GV)

Mounting hardwareU-clamp (UC), front flange (FF), retrofit flange (RF)

SocketThrottle plugs 0.007", 0.02", 0.063"


Process gauges

are .5% accuracy

Pressure psiCompound psi

0/15 30" Hg/15 psi

0/30 30" Hg/30 psi

0/60 30" Hg/60 psi

0/100 30" Hg/100 psi

0/160 30" Hg/150 psi

0/200 30" Hg/300 psi


0/400 Vacuum

0/600 30/0 in. Hg

0/800 34/0 ft H20





0/5000 NOTE: Equivalent standard kg/cm2, and kPa metric ranges are available.




diaphragm seals p46
Diaphragm Seals P46
  • Primary use: to Isolate the process from the gauge Allowing thick process and toxic chemicals;erosive;corrosive to be read accurately
  • Automatically derates to 1% BFSL
  • Types of Fills:
  • Glycerine:$ Freezes,Common and inexpensive
  • Silicone: more $$ but temperature stable
  • Fluorolube: $$$$ food Grade and Stable
  • Siphons: to isolate water/vapour from high temp steam.
  • Throttle the flow into and out of the gauge
  • Oversnubbing can block the flow and gauge will not move!!
  • Subject to plugging!
  • Use only on clean solids.!
  • Throttle screws can plug up too...
electronic measurement
Electronic Measurement
  • Strain Gauge P53
  • Capacitive element P54
  • LVDT inductance P55
  • Piezo Crystal P56
  • Capacative and Strain Gauge=90% market share!!
Capacitive: Requires more movement to sense .But is reliable technologyRosemount first ot come out with it.
differential pressure measurement
Differential pressure Measurement:
  • With orifice plates principally
  • used for flow detection and signal transmission
  • differential in Filters;room pressure
  • equivalent of two sensors interacting to one another.
that s it for tonight
That’s it for Tonight!



Pages 95-147 Temperature and Weight

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