Samson 4763 Mounting And Operating Instructions - Tends”
22
EB 8359-2 EN
Operation
7.3.2 Setting for actuator with
fail-safe action “stem ex-
tends”
Toensurethatthetotalclosingforceofthe
actuatoractsonthevalve,proceedasfol-
lows:
Î
Withdirectoperatingdirection<<:ad-
juststartingpointto4.5 mA(slightly
raised).
Î
Withreverseoperatingdirection<>:ad-
juststartingpointto19.5 mA(slightly
lowered).
Starting point (zero) e.g. 4.5 mA
1. Turnthezeroadjustmentscrew(4)until
theplugstemjuststartstomoveoutofits
restingposition(observetravelindica-
tor).
2. Reducetheinputsignalto0 mAand
slowlyincreaseitagain.Checkwhether
theplugstemstartstomoveatexactly
4.5 mAandcorrect,ifnecessary.
Upper range value (span) e.g. 20 mA
3. Oncethestartingpointhasbeenset,in-
creasetheinputsignal.Atexactly
20 mA,theplugstemmuststandstill,
havingmovedthrough100 %travel
(watchthetravelindicatoratthevalve).
Iftheupperrangevalueisincorrect,
movethepin(2)asfollowstocorrectit:
4. Movetowards
Leverend à Toincreasethetravel
Fulcrum
à
Toreducethetravel
Aftercorrectingtheinputsignal,re-ad-
justzero.Thenchecktheupperrange
valueagain.
Repeatthecorrectionprocedureuntilboth
valuesarecorrect.
7.3.3 Setting for actuator with
fail-safe action “stem re-
tracts”
Whenusinganactuatorwith"actuatorstem
retracts"fail-safeaction,thediaphragm
chambermustbepressurizedwithasignal
pressurethatishighenoughtotightlyclose
thevalveagainsttheupstreampressurein
theplant.
Î
Operatingdirection<<:Upperrange
valueofreferencevariable20 mA
Î
Operatingdirection<>:Lowerrangeval-
ueofreferencevariable4 mA
Therequiredsignalpressureiseitherindicat-
edonthepositionerlabelortherequired
supplypressurecanberoughlycalculatedas
describedinsection 6.4.
Starting point e.g. 20 mA
1. Settheinputsignalattheammeterto
20 mA.
Turnthezeroadjustmentscrew(4)until
theplugstemjuststartstomoveoutofits
initialposition.
2. Increasetheinputsignalandslowlyre-
duceitagainto20 mA.Checkwhether
theplugstemstartstomoveatexactly
20 mA.
Correctanydeviationatthezeroadjust-
mentscrew(4).Turningitcounterclock-