Samson TROVIS 3730-1, Translation Of Original Instructions, Page: 19 / 144

EB 8484-1 EN 3-1
Design and principle of operation
3 Design and principle of oper -
ation
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See Fig. 3-1
The TROVIS 3730-1 Electropneumatic Posi -
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-con-
tact 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 le-
ver, 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 travel
sensor (2) to the 4 to 20 mA DC control sig -
nal issued by the control system after it has
been converted by the A/D converter (3).
In case of a set point deviation, the activa-
tion of the i/p module (7) is changed so that
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 (9) for menu navigation on the dis-
play (11).
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).
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We recommend using a volume restric-
tion:
− For linear actuators with a transit
time <1 s (e.g. with an actuator area
smaller than 240 cm²)
− For rotary actuators with a volume of
less than 300 cm³.
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Actuators with a transit time ≥ 1 s do not
require the air flow rate to be restricted.
3.1.1 Options
The optional additional functions of the
TROVIS 3730-1 Positioner allows it to be
adapted to specific requirements.
Inductive limit contacts
Limit contacts with mechanical position pick-
up issue a signal to a control system when
the valve reaches one of the two adjustable
limits.
Inductive proximity switches are operated by
adjustable tags. For operation of the induc-
tive limit contacts, switching amplifiers must
be connected in the output circuit.