Samson Type 3766, Mounting And Operating Instructions

Page: 38 / 52

Adjusting the zero point
1. Use the input signal of the positioner to
move the valve to closed position (valve
CLOSED — travel 0 %).
2. The ammeter must now indicate ap-
prox. 4 mA.
3. Correct smaller deviations on the ZERO
potentiometer until the meter shows
exactly 4 mA.
If deviations are too high and cannot
be corrected using the potentiometer
(adjustment range of approx. 20 turns),
set the switches 1 and 2 to indicate an
mA value which is within the adjustment
range of the ZERO potentiometer.
4. Set the zero point to exactly 4 mA using
the ZERO potentiometer.
Adjusting the span
1. Use the input signal of the positioner to
move the valve to open position (valve
OPEN — travel 100 %).
2. The ammeter must now indicate ap-
prox. 20 mA.
3. Correct smaller deviations on the SPAN
potentiometer until the meter shows
exactly 20 mA.
If deviations are too high, set the swit-
ches 3 and 4 to indicate an mA value
which is within the adjustment range of
the SPAN potentiometer.
4. Turn the SPAN potentiometer until the
meter shows exactly 20 mA.
Since zero and span have a mutual in-
fluence on each other, repeat the correc-
tion procedure at both potentiometers
until both values are correct.
Note on adjusting the position transmitter
for positioners with NAMUR adapter hous-
ing
When the positioner and the position trans-
mitter signal have different operating direc-
tions (<< and <>), the zero point of the
transmitter signal could be unadjustable
due to the additional deflection caused by
the bracket (28, Fig. 7) of the adapter hous-
ing.
If so, readjust the black pointer (sec-
tion 2.2.2) so that the sensor of the position
transmitter reaches the control range.
Unscrew the clamp.
For “Actuator stem extends” (FA), shift the
pointer upward towards the actuator; for
"Actuator stem retracts" (FE), shift the
pointer downward towards the valve.
For valves with rod-type yoke, slightly shift
the positioner on the rod in downward (FE)
or upward (FA) direction.
Important!
Every time you have made a change as de-
scribed above, the zero point and span of
the positioner must be readjusted before
calibrating the position transmitter.
38
EB 8355-1 EN
Adjusting the position transmitter