Samson 4763 - Setting for Actuator with Fail-Safe Action Stem Extends; Setting for Actuator Version Stem Retracts

32 EB 8359-2 EN
Operating the positioner
6.3.2 Setting for actuator with
fail-safe action “stem
extends”
To ensure that the total closing force of the
actuator acts on the valve, proceed as fol-
lows:
Î With direct operating direction <<:
adjust starting point to 4.5mA (slightly
raised).
Î With reverse operating direction <>:
adjust starting point to 19.5mA (slightly
lowered).
Starting point (zero) e.g. 4.5mA
1. Turn the zero adjustment screw (4) until
the plug stem just starts to move out of its
resting position (observe travel indica-
tor).
2. Reduce the input signal to 0mA and
slowly increase it again. Check whether
the plug stem starts to move at exactly
4.5mA and correct, if necessary.
Upper range value (span) e.g. 20 mA
3. Once the starting point has been set,
increase the input signal. At exactly
20mA, the plug stem must stand still,
having moved through 100% travel
(watch the travel indicator at the valve).
If the upper range value is incorrect,
move the pin (2) as follows to correct it:
4. Move towards
Lever end à To increase the travel
Fulcrum à To reduce the travel
After correcting the input signal, re-ad-
just zero. Then check the upper range
value again.
Repeat the correction procedure until both
values are correct.
6.3.3 Setting for actuator version
“stem retracts”
When using an actuator with fail-safe action
"actuator stem retracts", the diaphragm
chamber must be pressurized with a signal
pressure that is high enough to tightly close
the valve against the upstream pressure in
the plant.
Î Operating direction <<: Upper range
value of reference variable 20mA
Î Operating direction <>: Lower range val-
ue of reference variable 4mA
The required signal pressure is either indicat-
ed on the positioner label or the required
supply pressure can be roughly calculated as
described in section5.4.2.
Starting point, e.g. 20mA
1. Set the input signal at the ammeter to
20mA.
Turn the zero adjustment screw (4) until
the plug stem just starts to move out of its
initial position.
2. Increase the input signal and slowly
reduce it again to 20mA. Check
whether the plug stem starts to move at
exactly 20mA.
Correct any deviation at the zero
adjustment screw (4). Turning it
counterclockwise causes the plug stem to