Samson Type 3766, Mounting And Operating Instructions

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In split-range operation, this value is re-
duced by half.
Turn the adjuster clockwise to reduce
the travel and counterclockwise to in-
crease it.
2. After correction has been completed,
shut off the input signal and slowly in-
crease it again.
Check the starting point and the upper
range value. Repeat the correction pro-
cedure until both values are correct.
4.1.3 Adjusting the actuator: "Actu-
ator stem retracts"
Important!
When using an actuator with fail-safe ac-
tion"Actuator stem retracts", the diaphragm
chamber must be pressurized with a signal
pressure that suffices to tightly close the
valve even when an upstream pressure is
applied in the plant. This applies to an
upper range value of the reference variable
(1 bar) and operating direction >> as well
as a lower range value of the reference vari-
able (0.2 bar) and operating direction <>.
The required signal pressure is either indi-
cated on the positioner label or can be
roughly calculated as described in sec-
tion 3.1.2.
Starting point (e.g. 1 bar)
1. Use the pressure adjuster to set the
input signal to 1 bar.
2. Turn the zero adjuster (6.2) until the
valve just starts to move from its initial
position.
3. Increase the input signal and slowly re-
duce it to 1 bar again. Check whether
the valve start to move at exactly 1 bar.
4. Correct any deviation on the zero adjus-
ter (6.2). Turning the adjuster counter-
clockwise causes the valve to move
from its end position earlier; turning
clockwise causes the valve to move
from its end position later.
Upper range value (e.g. 0.2 bar)
1. Once the starting point has been set,
adjust the control signal to 0.2 bar
using the pressure adjuster. At exactly
0.2 bar, the plug stem must stand still,
having passed through 100 % travel
(watch the travel indicator at the valve).
2. If the upper range value is incorrect,
turn the span adjuster (travel). Four
turns correspond to a travel change of
10 % in standard operation. In split-
range operation, this value is reduced
by half.
Turn the adjuster clockwise to reduce
the travel and counterclockwise to in-
crease it.
3. After correction has been completed,
reset the control signal to 1 bar.
4. Turn the zero adjuster (6.2) again until
the pressure gauge indicates the re-
quired signal pressure (see sec-
tion 3.1.2).
If no pressure gauge is available, set
the starting point to 0.97 bar instead.
EB 8355-1 EN
33
Adjusting the positioner at the valve