Instruction Manual
D101728X012
3710 and 3720 Positioners
September 2017
26
Zero and Span Adjustments
Figure 19. Features and Adjustments
W5947
NAMEPLATE
AREA
SCREENED
VENT OPENING
ZERO ADJ PIVOT
SPAN ADJ SHAFT
(THREADED ROD)
ZERO ADJUSTER
LOCK NUT
ZERO ADJUSTER
FEEDBACK
ARM ASSY
NOTES:
1THE SPAN ADJ ASSY IS MADE UP OF THE RANGE SPRING, SPAN ADJ SHAFT (THREADED ROD), AND SPAN ADJ KNOB.
2THE SPAN ADJ ASSY FEATURES A RED COLOR‐CODED RANGE SPRING FOR A 0.4 TO 2.0 BAR (6 TO 30 PSIG) INPUT SIGNAL.
SPAN ADJ ASSY
ACTION BLOCK
MOUNTING SCREW HOLE
SPOOL VALVE
INPUT MODULE
SUMMING BEAM ASSEMBLY
MOUNTING SCREW HOLE
CAM
MOUNTING
SCREW HOLE
1
SUMMING BEAM FLEXURE
2
1. To start this procedure, if necessary, unscrew the four captive cover screws (key 8) and remove the cover assembly
(key 7).
2. Apply supply pressure.
3. Provide a way to check the input signal. Apply the minimum input signal. For example:
D
For a 3710 pneumatic positioner, if the input signal range is 0.2 to 1.0 bar (3 to 15 psig), apply 0.2 bar (3 psig).
D
For a 3720 electro‐pneumatic positioner, if the input signal range is 4-20 mA, apply 4 mA to the 3722 converter.
Note
The zero adjustment locknut and zero adjustment knob are identical parts, key 35.
4. Loosen the zero adjustment locknut (key 35) and turn the zero adjustment knob (key 35) until the actuator moves
the valve to the proper position. This valve position must correspond to the minimum input signal.