Data Sheet

3610J and 3620J Positioners
D200064X012
Product Bulletin
62.1:3610
February 2015
7
Figure 4. Schematic of Fisher 3620JP Positioner
38A8900-B
B2148
FOR 3620JP
ONLY
MINOR LOOP
GAIN ADJ
FLAPPER
NOZZLE
FIXED
RESTRICTION
CROSS-OVER
ADJ
RELAY BEAM
RELAY
A
RELAY
B
SUMMING BEAM
AIR
SUPPLY
FINE
SPAN
ADJ
PIVOT
B
FEEDBACK
LEVER
POSITIONER
CAM
RANGE SPRING
COUNTER SPRING
COARSE
SPAN
ADJ
INPUT MODULE
PIVOT A
CAVITY A
CAVITY B
ZERO ADJ
PISTON
ACTUATOR
CONVERTER
MODULE
SUPPLY
END VIEW OF ROTARY SHAFT
4-20 MILLIAMPERE INPUT SIGNAL
-
+
SUPPLY PRESSURE
NOZZLE PRESSURE
INPUT SIGNAL
OUTPUT SIGNAL
OUTPUT SIGNAL
These positioners are force-balanced instruments that
provide a valve shaft position proportional to the input
signal. The following describes the principle of
operation for 3610JP and 3620JP positioners. The
principle of operation for 3610J and 3620J positioners
is similar except relay A is not used. Refer to figures 3
and 4 while reading the following descriptions.
For direct action, input signal pressure from a control
device is channeled to cavity A in the input module. An
increase in input signal pressure results in a downward
force on the summing beam, pivoting the
summing beam counterclockwise. This moves the
flapper slightly toward the nozzle, increasing the
nozzle pressure. As nozzle pressure increases, the relay
beam pivots clockwise, causing relay B to increase
upper cylinder pressure and relay A to exhaust lower
cylinder pressure of the actuator.
As a result, the actuator rod extends and the actuator
rotary shaft rotates clockwise. This causes the
feedback lever to pivot clockwise and the force applied
to the summing beam by the range spring increases.
This force, which opposes the downward force on the
summing beam caused by the increasing input signal