Design And Principle Of Operation; Additional Equipment (Positioner) - Samson 5857 Mounting And Operating Instructions

3 Design and principle of oper-
ation
Î See Fig. 3-1.
The three-step version of the electric actuator
consists of a reversible synchronous motor
and a maintenance-free gear. In the version
with digital positioner, a stepper motor al-
lows for supply by frequency-independent
voltages.
The control signal of the controller is connect-
ed to the terminals eL and aL of the actuator.
If voltage is applied to eL, the actuator motor
retracts the actuator stem. If voltage is ap-
plied to aL, the actuator motor extends the
actuator stem.
The actuator is connected to the valve by a
coupling nut (4) which provides a force-lock-
ing connection between the actuator stem
and the plug stem of the valve.
The control signal from the input side is
transferred over the motor and the connected
gear and used as the positioning force to
move the actuator stem. When the actuator
stem (3) extends, the valve is closed, oppos-
ing the force of the valve spring (7). When
the actuator stem retracts, the valve is
opened as the plug stem (6) follows the mo-
tion of the return spring.
The motor is switched off by torque-depen-
dent limit switches when an end position is
reached or in case the motor is overloaded.
Travel and direction of action can be read
off the travel indicator (5) on the side of the
actuator housing.
EB 5857 EN

Design and principle of operation

The actuator has a handwheel that is used to
manually position the valve when the actua-
tor is de-energized.
The Type 5857 Actuator can be combined
preferably with SAMSON Types 3222,
3222 N, 2488 and 2488 N Valves as well
as special versions of Type 3260 and
Type 3226 Valves.
3.1 Additional equipment
(positioner)
The actuator is available with a digital posi-
tioner.
The positioner ensures a predetermined as-
signment of the valve position to the input
signal. A 0 to 10 V signal can be picked up
at the brown (BN) and green (GN) wires for
position indication (see the 'Installation' sec-
tion for connection).
The characteristic and the input and output
signal settings can be changed using the
TROVIS-VIEW software (u EB 6661).
The version with positioner allows the char-
acteristic to be reversed and is suitable for
split-range operation.
3-1