Emerson Fisher KC Series Instruction Manual page 34

4195KA, KB, KC, and KS Controllers
SET POINT
INDICATOR
PROCESS POINTER
REMOTE SET POINT
CONNECTED HERE
INPUT ELEMENT
CONNECTED HERE
CONNECTING
LINK
BEAM
SUPPLY PRESSURE
OUTPUT PRESSURE
NOZZLE PRESSURE
RESET PRESSURE
PROPORTIONAL PRESSURE
46A9764-B
C0593-3 / IL
A 4195KC Series controller also has a rate valve as
shown in figures 4-6 and 4-7. This valve is an
adjustable restriction that momentarily increases the
controller gain to accelerate the corrective action for
slow pressure systems. A
proportional-plus-reset-plus-rate controller responds
to a change in process pressure as follows:
4-12
RESET BELLOWS
PROPORTIONAL
BELLOWS
FLAPPER
NOZZLE
PROPORTIONAL-PLUS-RESET-PLUS-RATE CONTROL
TO
PROPORTIONAL
BELLOWS
DIFFERENTIAL
RELIEF VALVE
Figure 4-6. 4195KC Series Controller Schematic
PROPORTIONAL
BAND ADJUSTMENT
SUPPLY
PRESSURE
RATE VALVE
RESET VALVE
TO
RESET
TO
BELLOWS
NOZZLE
RATE VALVE
RESET VALVE
PROPORTIONAL-PLUS-RESET-PLUS-RATE CONTROL
WITH ANTI-RESET WINDUP
D First, the rate action delays the proportional
action just long enough to allow the controller to
respond to the change quickly with high gain, but not
long enough for the high gain to cause instability.
D Then, the low gain provided by the proportional
action keeps the system stable. Finally, reset action
slowly increases the gain and returns the process
pressure toward the set point.
Instruction Manual
REVERSE ACTION
QUADRANT
FEEDBACK
LINK
FEEDBACK
MOTION
DIRECT ACTION
QUADRANT
INPUT MOTION
FLAPPER DETAIL
OUTPUT PRESSURE
TO FINAL CONTROL
ELEMENT
RELAY
OUTPUT
RELAY
SUPPLY
PRESSURE
Form 5207
April 2007
FLAPPER
PIVOT