Settings For Actuator With "Actuator Stem Extends" Fail-Safe Action; Settings For Actuator With "Actuator Stem Retracts" Fail-Safe Action - Samson 3767 Mounting And Operating Instructions

Operation
5.1.2 Settings for actuator
with "actuator stem ex-
tends" fail-safe action
Starting point (e.g. 4 mA)
1. Set the input signal at the ammeter to
4.5 mA
2. Turn the zero adjuster (6.2) until the
valve just starts to move from its initial
position.
3. Reduce the input signal to 0 mA and
slowly increase it again. Check whether
the valve starts to move at exactly
4.5 mA. Correct any deviation at the
zero adjuster (6.2).
Upper range value (span) e.g. 20 mA
1. Once the starting point has been set,
increase the input signal to 20 mA at the
ammeter.
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, turn the
span adjuster (travel). Four turns correspond
to a travel change of 10 % in standard oper-
ation. In split-range operation, this value is
reduced by half.
Turn the adjuster clockwise to reduce the
travel and counterclockwise to increase it.
2. After the correction has been completed,
reduce the input signal and slowly
increase it again.
Check the starting point and the upper
range value. Repeat the correction pro-
cedure until both values are correct.
40
NOTICE
When setting the zero adjuster (6.2),
check whether the actuator is relieved
of pressure.
When the input signal is 4 mA and
the operating direction >>, or the in-
put signal is 20 mA and the operat-
ing direction <>, the pressure gauge
must indicate 0 bar.
Correct zero accordingly.
5.1.3 S ettings for actuator with
"actuator stem retracts"
fail-safe action
NOTICE
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 pres-
sure in the plant. This applies to an
upper range value of the reference
variable (20 mA) with operating di-
rection >> as well as a lower range
value of the reference variable
(4 mA) with operating direction <>.
The required signal pressure is either indi-
cated on the positioner label or the required
supply pressure can be roughly calculated as
described in section 4.1.2.
Starting point (e.g. 20 mA)
1. Set the input signal at the ammeter to
20 mA
EB 8355-2 EN