Samson 3767 - Operation; Tuning the Positioner Mounted onto the Control Valve

38 EB8355-2EN
Operation
5 Operation
5.1 Tuningthepositioner
mountedontothecontrol
valve
Startingpointandreferencevariable
When adjusting the positioner directly at the
controlvalve,thetravel(openingangle)must
beadaptedtothereferencevariable.
Withareferencevariable,forexample,4to
20mA,thevalvemustmovethroughitsen-
tiretravelrangefrom0to100%(Fig.13,
left).
For positioners for rotary actuator, an open-
ingangle,forexample,0to70°mustbeas-
signedtothereferencevariable.
ThestartingpointisbasedontheCLOSED
position of the valve.
Depending on the actuator version ("actua-
torstemextends"or"actuatorstemretracts")
and the operating direction of the positioner
(>>or<>),thisstartingpointcanbeeither
thelowerorupperrangevalue(4or20mA)
ofthereferencevariable.
Thereferencevariablerangeandthusthe
upper range value determine the travel of
the valve.
Insplit-rangeoperation(Fig.13,right),the
control valves work with smaller reference
variableranges.Thecontrolleroutputsignal
is used to control two control valves, dividing
it such that the valves move through their en-
tire travel range at half the input signal
rangeeach(e.g.rstvalvesetto4to
12mA,secondvalvesetto12to20mA).To
avoidoverlapping,allowforadeadbandof
±0.5mAasshowninFig.13.
The startingpoint(zero)isadjustedatthe
zero adjuster (6.2); the span, i.e. the upper
range value, is adjusted at the span adjuster
(6.1).
Duringtheadjustment,connectasuitable
ammeter to the signal input and apply air to
the supply air input.
NOTICE
When the positioner is controlled by
a computer whose signal is limited,
e.g. between 4 to 20mA, set the po-
sitioner to the range from 4.5 to
20mA.
This is the only way to ensure that the
actuator is completely vented and the
valve completely closed when the
controller issues a 4mA signal.
For operating direction <>, set the
range to 4 to 19.5mA.