Samson 4763 Mounting And Operating Instructions - Ation
10
EB 8359-2 EN
Design and principle of operation
4 Design and principle of oper-
ation
Theelectropneumaticpositionerisusedto
assignthevalveposition(controlledvariable)
totheinputsignal(referencevariable).The
positionercomparesthecontrolsignalofa
controlsystemtothetravelofthecontrol
valveandissuesasignalpressure(output
variable)forthepneumaticactuator.
Thepositionerconsistsofanelectropneumat-
icconverterunit(21)andapneumaticunit
equippedwithalever(1),shaft(1,1)and
rangespringaswellasthepneumaticcon-
trolsystemwithnozzle,flapperplateand
booster.TheDCcontrolsignal,e.g.4to
20 mA,issuedbythecontroller,istransmit-
tedtotheelectropneumaticconverterunit
(i/pconverter)whereitisconvertedintoa
proportionalpressuresignalp
e
.
Anychangeoftheinputcurrentsignalcaus-
esaproportionalchangeoftheairpressure
p
e
fedtothepneumaticcontrolsystem.
Theairpressurep
e
producesaforcewhich
actsonthesurfaceofthemeasuringdia-
phragm(8)andiscomparedtotheforceof
therangespring(6).
Themotionofthemeasuringdiaphragm(8)
istransferredtotheflapperplate(10.2)over
thefeelerpin(9.1),andthenozzle(10.1)
releasespressure.Anychangeofeitherthe
airpressurep
e
orthevalvestemposition
causesthepressuretochangeinthebooster
(12)connecteddownstreamofthenozzle.
Thesignalpressurep
st
whichisreleased
causestheplugstemtoassumeaposition
basedonthereferencevariable.
TheadjustablevolumerestrictionQ(14)and
Xp(gain)restriction(13)areusedtoopti-
mizethecontrolloopofthepositioner.
Therangespring(6),whichcanbeex-
changed,isassignedtoboththeratedvalve
travelandthespanofthereferencevariable.
Legend for Fig. 1 and Fig. 2
1
Leverforvalvetravel
1.1
Shaft
2
Pin
2.1
Nut
3
Sleeve
4
Zeropointadjustment
5
Fasteningscrew
6
Rangespring
6.1
Bracket
7
Fasteningscrew
8
Measuringdiaphragm
9
Diaphragmplate
9.1
Feeler pin
10
Nozzleblock
10.1 Nozzle
10.2 Flapperplate
11
Coverplate
12
Booster
13
Xprestriction
14
VolumerestrictionQ
15
Holeforfasteningscrew
20
Plate
21
i/pconverter