Samson Type 3766 - Page 39

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 approx.
4 mA.
3. Correct smaller deviations on the ZERO
potentiometer until the meter shows ex
-
actly 4 mA.
If deviations are too high and cannot be
corrected using the potentiometer (ad
-
justment 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 approx.
20 mA.
3. Correct smaller deviations on the SPAN
potentiometer until the meter shows ex
-
actly 20 mA.
If deviations are too high, set the
switches 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 in Fig. 7) of the adapter hous
-
ing.
If so, readjust the black pointer (section
2.2.2 on page 16) so that the sensor of the
position transmitter reaches the control
range.
Unscrew the clamp. For “Actuator stem ex-
tends” (FA), shift the pointer upward to-
wards the actuator; for "Actuator stem re-
tracts" (FE), shift the pointer downward to-
wards the valve. For valves with rod-type
yoke, slightly shift the positioner on the rod
in downward (FE) or upward (FA) direction.
Note: Every time you make a change as de
-
scribed above, the zero point and span of
the positioner must be readjusted before cal
-
ibrating the position transmitter.
EB 8355-1 EN 39
Operation