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Process Control Concepts
Process Control is to maintain certain processvariables (PV) of a process at a esire level (!etValues)
Instruments are use to obtain information aboutt"e process variables (PVs)
Controller ( a soft#are pro$ram resient in %C!)calculates t"e ifference bet#een !V an PV anaccorin$l sens a si$nal' calle ManipulateValue (MV) to final control elements (Valves'Vanes etc)
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Pressure Measurement
bsolute Pressure* Measure over totalvacuum./ero absolute
tmosp"eric.Barometric Pressure* Pressuree+erte b Eart"0s atmosp"ere
%ifferential Pressure* %ifference bet#een t#o pressures 1au$e Pressure* Pressure over t"e atmosp"eric
Pressure 2rostatic Pressure* Pressure e+erte b a li3ui
column
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Pressure Measurement
4ine Pressure.5orkin$ Pressure.!tatic Pressure*
Pressure e+erte b a flo#in$ flui on t"e pipe
surfaces %namic Pressure* Pressure e+erte b a flo#in$
flui parallel to t"e flo# irection
Vacuum* Pressure belo# t"e atmosp"eric pressure
Compoun Pressure* Measure from a reference
#"ic" is neit"er atmosp"eric nor total vacuum
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Mission !tatement
clear statement of our compan0s lon$6
term mission ,r to use #ors t"at #ill
"elp irect t"e $ro#t" of our compan' but be as concise as possible
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Pressure Measurement
%evices Pressure is a force applie.istribute over a
surface
Pressure measurement is use for pressure itself'flo#' level an even temperature
ll measurement sstems consists of *
7 Primar Element #"ic" inirectl. inirectl in contact
#it" flui an interacts #it" pressure c"an$es
7 !econar Element #"ic" translates t"is interaction
into values for use in inication' recorin$ an control
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Pressure Measurement %evices 7
!econar Elements
Mec"anical ,ransucers
7 Bello#s
7 Bouron ,ubes
7 %iap"rams
7 -orce Balanc
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Pressure Measurement %evices 7
!econar Elements
Electronic ,ransucers
7 Variable Capacitance
7 Variable Reluctance
7 Vibratin$ 5ire
7 Variable Resistance
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Mec"anical ,ransucers
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4evel Measurement
4evel measurement is ivie into t#o $roups*%irect 4evel an Pressure6operate
%irect 4evel Measurement* 7 2ook tpe
7 !i$"t 1lass
7 -loat 1au$in$
Pressure6Operate Measurement* 8se is mae of
t"e fact t"at pressure oes not epen on t"ecross6sectional area of a vessel' in stea it epenson li3ui "ei$"t an ensit
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%irect 4evel 6 4evel 1au$es
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4evel 1au$es
%irectin$ 4evel reain$ evice
,pes * ,ransparent an Reflu+
,ransparent tpe is use for*
7 Caustic' ciic' 2eav 2C services' 2i$" pressure
7 Coate #it" protective Mica
Reflu+ tpe is use for li$"t services*
7 9on6corrosive' non6viscous' Clear 2C 7 It "as special optical propert for clear emarcation
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4evel 1au$es
5"ile commissionin$' open t"e :er$usonvalve partiall till t"e $a$e is pressure up .
#arme up5"ile in service' ;er$uson valve s"all be
full in open conition
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Close Vessels 7 %ifferential
Pressure pproac"
" = P .>$ In close vessles' pressure above t"e li3ui affects
t"e pressure measure at t"e bottom ,o measure t"e true level' t"e vessel pressure must
be subtracteMakin$ a pressure tap at t"e top of t"e vessel an
connectin$ t"is to 4P sie accomplis"es t"is
%r 4e$* If $as is non6conensable5et le$* Conense 4i3ui introuces error
2ence calibrate #it" a reference li3ui
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4evel Measurement in Close
Vessels
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,emperature Measurement
,emperature is e$ree of "otness.colness
on a efinite scale
oC = ?.@ (o- 7 A)Most reliable met"os of measurement*
7 Bimetallic
7 ,"ermocouples
7 R,%
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,emperature Measurement
ll temperature $a$es uses bimetallic principles
Bimetallic Principles*
7 Metals c"an$e in volume in response to temperature 7 an ifferent metals respon ifferentl to c"an$e in
temperature
Its accurac is not as $oo as a $lass t"ermometer
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,emperature Measurement
Bimetallic 1a$e
Bimetallic Principles*
7 Metals c"an$e in volume in response to temperature
7 an ifferent metals respon ifferentl to c"an$e in temperature
ll temperature $a$es uses bimetallic principles
Most reliable met"os of measurement*
7 Bimetallic
7 ,"ermocouples
7 R,%
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,"ermocouples
!ummari/e
competition
Outline ourcompan0s
competitive avanta$e
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,"ermocouples
It is a t"ermoelectric temperature measurin$evice
It is forme b pressin$ t#o issimilar metals in
series5"en t"e ;unctions are at ifferent tempertures'
emf is $enerateMeasurin$ ;unction."ot ;unction is inserte into
t"e meium of #"ic" temperature is inserte Col :unction.Reference ;unction is inserte in t"e
measurin$ evice
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Resistance ,emperature
%etectors
8ses t"e c"an$e in resistance in response to
c"an$e in temperature
Resistance epen on metal si/e anresistivit of t"e metal
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-lo# Measurement
Orifice
7 Orifice ma be concentric or eccentric
7 Orifice plats constricts t"e flo# to prouce aifferential pressure
7 ,"e result is a "i$" pressure upstream an a
lo# pressure o#n stream
7 %p is proportional to t"e flo#
7 Orifice meters are ine+pensive
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-lo# Measurement
Venturi
7 4o# Pressure
7 2i$"l accurate
7 Bi$ !i/e Pipe
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nnubar
8ses Pitot ,ube
Principle
-lo# is proportionalto pressure rop
8ses multiple ports
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-lo# Measurement
rea Meters*
7 In "ea flo# meters' t"e restriction area kept
constant $eneratin$ a pressure ifferential 7 5"ere as in area meter' a variable area "ols
ifferential pressure constant
7 C"an$e in area is a measure of flo# rate
7 E+* Rotameter
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Rotameter6 !uitable for lo# flo#s
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Valves 7 Valve is a variable
Orifice
Valve ,pes*
7 Plu$6in6seat
7 Rotatable Plu$ 7 Rotatin$ Vane
7 Eccentric Rotation
7 Ca$e6$uie 7 %eformable -lo# Passa$e
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Ball Valve.Plu$ Valve
6 Rotatable Plu$
Plu$.ball rotate
,"rou$" a 3uarter
of a turn,"e ball "as a passa$e
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Butterfl valve. %ampers 7
Rotatin$ Vane
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Valve ccessories
ctuators* ,ranslates control si$nal intoaction' e$*Motors' %iap"rams' solenois'
cliners,ransucers an Positioners* Convert
electronic si$nals into pneumatic."raulic pressures t"at control actuators.valves
Positioner is use #"en more accurate positionin$ of valve steam is re3uire
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T%ere are t&o #asic "esi'ns o 'ate va!ves insi"e
scre& ste* an" otsi"e scre& ste*+Seatin' is perpen"ic!ar or at ri'%t an'!es to t%e !ine
o !o& , *eets it %ea" on+Repeate" *ove*ent o t%e &e"'e near t%e point o
c!osre n"er %i'% ve!ocit- !o& *a- create a "ra' ont%e seatin' sraces an" case 'a!!in' or scorin' on
t%e "o&nstrea* si"e+ A s!i'%t!- opene" &e"'e *a- a!so case tr#!ent
!o& &it% vi#ration an" c%atterin' o t%e &e"'e+
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Globe valve seating is parallel to the line offlow. A!! contact #et&een seat an" "isc en"s
&%en !o& #e'ins+ T%ese are a"vanta'es or
*ore eicient t%rott!in' o !o& &it% *ini**
&ire "ra&in' an" seat erosion+
.!o#e va!ves are 'enera!!- i"ea! or t%rott!in'
an" preera#!e or reent operation+
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Btter!- Va!ves are o t%e arter trn
a*i!- an" are so "esi'ne" #ecase a 01
"e'ree trn o t%e operator !!- opens or
c!oses t%e va!ve+
+ In so*e cases t%e- *a- #e se" ornon,critica! t%rott!in' app!ications+ T%e-
are !i'%ter in &ei'%t t%an conventiona!
va!ves+