Samson 4763 Mounting And Operating Instructions - Ence Variable
20
EB 8359-2 EN
Operation
7.2 Starting point and refer-
ence variable
Theattachedleverandtheinstalledrange
springofthepositionerareassignedtothe
valuesofratedvalvetravelandthereference
variableasinTable1.
Innormaloperation,thereferencevariable
spanis100 %=16 mA.Asmallerspanof,
forexample,50 %=8 mAisonlyrequired
forsplit-rangeoperation(Fig. 12).
Thespancanbechangedbyexchangingthe
rangespring(section 7.4).Onmakingad-
justmentstothepositioner,thetravelmustbe
adaptedtothereferencevariableandvice
versa.
Withareferencevariable,forexample,4to
20 mA,thevalvemustmovethroughitsen-
tiretravelrangefrom0to100 %.Thestart-
ingpointthenis4 mAandtheupperrange
value20 mA.
Insplit-rangeoperation,thecontrolleroutput
signalisusedtocontroltwocontrolvalves,
dividingitsuchthatthevalvesmovethrough
theirentiretravelrangeathalftheinputsig-
nalrangeeach(e.g.firstvalvesetto4to
12 mA,secondvalvesetto12to20 mA).To
avoidoverlapping,allowforadeadbandof
±0.5 mAasshowninFig. 12.
Thestartingpoint(zero)isadjustedatthe
screw(4);thereferencevariablespan,i.e.
theupperrangevalue,isadjustedatthepin
(2).
7.3 Adjustment after mounting
the positioner on the valve
Î
Connectanammetertothecontrolsignal
inputattheterminals11(+)and12(–).
Î
Connectthesupplyairtothesupplyin-
put(supply9).
7.3.1 Setting the air delivery
(volume restriction Q) and
proportional band Xp
1. Closethevolumerestriction(14)asfar
astherequiredpositioningspeedper-
mits.
Checkthepositioningspeedbypushing
therangespring(6)asfaritwillgo.
2. Adjustthereferencevariableattheinput
toapprox.50 %ofitsrange.Then,turn
thezeroadjustmentscrew(4)untilthe
valveisatapproximately50 %valve
travel.
OnsettingtheXprestriction,observethere-
lationshipwiththesupplyairpressureasin-
dicatedinFig. 13.ThepresetvalueofXp
shouldbeapproximately3 %.
3. Checktheplugstem'stendencytooscil-
latebypressingtherangespring(6)
brieflyasfarasitwillgo.
TheXpvalueistobeadjustedtobeas
smallaspossible,withoutconsiderable
overshootingoccurring.
Additional points that apply concerning ad-
justment:
Î
AlwaysadjusttheXprestrictionbefore
settingthestartingpoint.