Instruction Manual
D200160X012
4195K Controllers
July 2018
37
The input element is connected to the process pointer and to the flapper by connecting links. As the process pressure
increases (in a direct‐acting controller), the flapper moves toward the nozzle, restricting flow through the nozzle and
increasing nozzle pressure. When this occurs, relay action increases the output pressure (delivery) of the controller.
Output pressure is fed back to the proportional bellows and to the reset bellows. The action of the proportional
bellows quickly counteracts the flapper movement that resulted from the process pressure change and backs the
flapper away from the nozzle.
Figure 4‐5. Fisher 4195KB Controller Schematic
SET POINT
INDICATOR
PROCESS POINTER
REMOTE SET POINT
CONNECTED HERE
INPUT ELEMENT
CONNECTED HERE
CONNECTING
LINK
BEAM
FLAPPER
NOZZLE
PROPORTIONAL
BELLOWS
RESET BELLOWS
PROPORTIONAL
BAND ADJUSTMENT
SUPPLY PRESSURE
RELAY
OUTPUT PRESSURE
TO FINAL CONTROL
ELEMENT
REVERSE ACTION
QUADRANT
FLAPPER
PIVOT
FEEDBACK
LINK
FEEDBACK
MOTION
DIRECT ACTION
QUADRANT
INPUT MOTION
FLAPPER DETAIL
SUPPLY PRESSURE
OUTPUT PRESSURE
NOZZLE PRESSURE
RESET PRESSURE
RELAY
TO NOZZLE
TO
RESET
BELLOWS
TO
PROPORTIONAL
BELLOWS
SUPPLY
PRESSURE
RESET
VALVE
DIFFERENTIAL
RELIEF VALVE
OUTPUT
PROPORTIONAL‐PLUS‐RESET CONTROL
PROPORTIONAL‐PLUS‐RESET CONTROL WITH ANTI‐RESET WINDUP
46A9764-C
B1908-4
RESET
VALVE
Pressure in the reset bellows opposes the action of the proportional bellows and slowly moves the flapper closer to the
nozzle. The result of this interaction is that, when the process pressure changes, proportional action temporarily
reduces the gain of the controller for improved stability. The process pressure then slowly returns to set point, as
pressure in both bellows equalizes via the reset action.
Moving the set point indicator changes the distance between the nozzle and flapper as does a change in process
pressure, except that when the set point is changed, the nozzle moves with respect to the flapper.