Instruction Manual
D103292X012
C1 Controllers and Transmitters
March 2017
29
The action is similar with falling output pressure. Lower feedback pressure lowers the bellows pressure, which moves
the flapper away from the nozzle. This again reduces the output pressure and continues until the output pressure is
zero.
Figure 14. Schematic of Reverse-Acting Proportional-Plus-Reset
Controller with Anti-Reset Windup
ARROW DOWN-RELIEVES
ON DECREASING OUTPUT
ARROW UP-RELIEVES
ON INCREASING OUTPUT
CONSTANT SUPPLY
PRESSURE
TO FINAL
CONTROL
ELEMENT
EXHAUST
RESET BELLOWS
RESTRICTION
RESET VALVE
GE23697-A
GE34724-A
E1063
SENSED
PRESSURE
PROPORTIONAL
BELLOWS
SENSED PRESSURE OUTPUT PRESSURE NOZZLE PRESSURE RESET PRESSURE
DIFFERENTIAL
RELIEF VALVE
CANTILEVER
SPRING
PRESSURE
SETTING DIAL
PROPORTIONAL
BAND ADJUSTMENT
KNOB
PRESSURE
SETTING KNOB
(OUTPUT AT ZERO
DURING SHUTDOWN)
(OUTPUT AT SUPPLY
DURING SHUTDOWN)
Transmitters
Action of a pneumatic transmitter is similar to that of a proportional-only controller. Since the output pressure of the
transmitter has no effect on the process pressure, transmitter output pressure is a proportional measure of the
process pressure. The proportional band adjustment determines the span of the transmitter, and the pressure setting
mechanism determines the zero of the transmitter.