Fundamentals of Industrial Control WEEK 3

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Fundamentals of Industrial Control
WEEK 3

• This week Pressure Measurement
• Terminology
• Pressure Sensor Technology

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How was it last Week?

• Recap of last Week
• Remember the terms?
• Types of Level sensors
• Did we miss any?
• Homework done?!

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What are Sensors?

• 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

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Transducers

• 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

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Terminology

• RANGEMin/Max design in normal operation
• ZeroWhere the measurment starts
• Zero DriftWhen the signal varies from its
  initial setting.
• Short Term DriftError expected immediately
• Long Term Drift Aging of components in which we
  have no control over

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Terminology

• SensitivityThe 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

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Terminology

• LinearityA sensor s function to have an output
  in a linear relationship to its output.
• BSL Best Straight Line method
• Examples on non linear sensors
• HysteresisSensors Reaction to the rise and fall
  of its initial input vs. its output reaction to
  input change.

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Confusion 101

• ACCURACY AND PRECISION
• Accuracycloseness of the true value of the
  variable being measured.
• Precisionreproducibility of doing it over and
  over again.

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Pressure Measurement

• Pressure can be created either compression(
  pumping)
• Or Expansion in a closed vessel
• Or by Gravitational exertion in a vessel

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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

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Same idea but on a closed vessel

• Pressure will increase in a vessel if the
  temperature increases which causes expansion

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Gas Laws

• Boyles Law P1V1P2V2 works as long as
  temperature is kept constant
• Charles LawV1/T1V2/T2 works as long as pressure
  is kept constant
• Idela Gas law P1V1/T1P2V2/T2 works on the day
  to day applications!

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Pressure Measurement

• Law Class 101 is now finished for the Day...

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Pressure Measurment Basics

• Manometers U tube and Inclined designs
• Great for low pressures
• Still used for low pressure lt10 psi applications

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U -Tubes

• 27.8 of H2O1 PSI

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

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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

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Is It Break Time Yet ?
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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

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• 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.
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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.
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Spiral Type

• P44
• Same idea as bourdon except very expensive to
  make and lower pressure capabiltiy
• Also known as a helical element

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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.

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Dual Scale Range Graduations Inner
Scale Outer Scale Inner Scale Outer
Scale Figure Intervals Minor Grad. Figure
Intervals Minor 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
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Type number 1008A/AL Size 63mm (2.5"), 100mm
(4") Case 304 stainless steel, dry (1008A), or
liquid filled (1008AL) Fill fluid Glycerin Ring
304 stainless steel, crimped Window
Polycarbonate Dial Black figures on white
background, aluminum Pointer Black,
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) Movement Patented PowerFlexTM
with polyester segment
Socket Brass, with O-ring case seal Restrictor
Brass throttle plug 0.013" orifice in all ranges
(except vacuum and 15 psi ranges) Connection
.25 NPT lower and back Ranges Vac. thru 15,000
psi and compound. Equivalent metric ranges
available Accuracy ASME B40.1, Grade B,
3-2-3 Operating temperature Dry gauge -40 F to
150 F Glycerine filled 20 F to 150 F
Silicon filled -40 F to 150 F Gauge
Options Case Sealed case, field-fillable (LJ)
Silicone filled (GV) Mounting hardware U-clamp
(UC), front flange (FF), retrofit flange
(RF) Socket Throttle plugs 0.007", 0.02", 0.063"
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• Process gauges
• are .5 accuracy

Pressure psi Compound 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 0/300 0/400 Vacuum 0
/600 30/0 in. Hg 0/800 34/0 ft
H20 0/1000 0/1500 0/2000 0/3000 0/5000 NO
TE Equivalent standard kg/cm2, and kPa metric
ranges are available. 0/10,000 0/20,000 0/30
,000
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• Grades of gauge Accuracies
• 3-2-3 rule!

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Diaphragm Seals P46

• Primary use to Isolate the process from the
  gauge Allowing thick process and toxic
  chemicalserosivecorrosive 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

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Diaphragm Seals
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Diaphragm seals
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Accessories

• Siphons to isolate water/vapour from high temp
  steam.

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Snubbers

• 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 fluids..no solids.!
• Throttle screws can plug up too...

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Electronic Measurement

• Strain Gauge P53
• Capacitive element P54
• LVDT inductance P55
• Piezo Crystal P56
• Capacative and Strain Gauge90 market share!!

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Strain Gauge
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Capacitive Requires more movement to sense .But
is reliable technologyRosemount first ot come
out with it.
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Piezo Crystal
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Variations of gauges and switches
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Differential pressure Measurement

• With orifice plates principally
• used for flow detection and signal transmission
• differential in Filtersroom pressure
• equivalent of two sensors interacting to one
  another.

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Thats it for Tonight!

• Questions/Applications/Arguments??
• Homework..!
• Pages 95-147 Temperature and Weight
• In troubleEmail me!!