
EB 8484-3 EN 3-1
Design and principle of operation
3 Design and principle of oper-
ation
ÎSeeFig.3-1
TheTROVIS3730-3ElectropneumaticPosi-
tioner is mounted on pneumatic control
valves and used to assign the valve position
(controlled variable x) to the control signal
(set point w). The positioner compares the
electric control signal of a control system to
the travel or opening angle of the control
valve and issues a signal pressure for the
pneumatic actuator.
The positioner mainly consists of a non-
contact travel sensor system (2), pneumatics
and the electronics with the microcontroller
(4). The valve position is transmitted either as
an angle of rotation or a travel to the pick-
up lever, from there to the travel sensor (2)
and forwarded to the microcontroller (4).
The PID algorithm in the microcontroller
compares the valve position measured by the
travelsensor(2)tothe4to20mADC
control signal issued by the control system
afterithasbeenconvertedbytheA/D
converter (3).
In case of a set point deviation, the activa-
tionofthei/pmodule(7)ischangedsothat
the actuator of the control valve (1) is pres-
surized or vented accordingly over the
downstream booster (6). As a result, the clo-
sure member of the valve (e.g. plug) is
moved to the position determined by the set
point.
The positioner is operated by a rotary push-
button (10) for menu navigation on the
plain-text display (11).
TheextendedEXPERTplusdiagnosticsarein-
tegrated into the positioner. They provide in-
formation on the control valve and positioner
and generate diagnostic and status messag-
es, which allow faults to be pinpointed
quickly.
3.1 Additional equipment
Volume restriction
The volume restriction Q serves to adapt the
air output capacity to the size of the actua-
tor.
The volume restriction is a screw restriction
which is screwed into the signal pressure
output of the positioner (or output of the
pressure gauge bracket or connecting plate).
ÎWe recommend using a volume restric-
tion
− For linear actuators with a transit
time<1s(e.g.withanactuatorarea
smallerthan240cm²)
− For rotary actuators with a volume of
lessthan300cm³
ÎActuatorswithatransittime≥1sdonot
requiretheairowratetoberestricted.