Principle Of Operation For 4195Ka Series Controllers; Overall Operation - Emerson Fisher KC Series Instruction Manual

Instruction Manual
Form 5207
April 2007
SET POINT INDICATOR
PROCESS POINTER
REMOTE SET POINT
CONNECTED HERE
INPUT ELEMENT
CONNECTED HERE
CONNECTING
LINK
BEAM
SUPPLY PRESSURE
OUTPUT PRESSURE
PROPORTIONAL PRESSURE
NOZZLE PRESSURE
46A9764-A
B1489-2 / IL
7. The controller output should be 0.62 ±0.02 bar (9
±0.25 psig) or 1.2 ±0.04 bar (18 ±0.5 psig). If not,
adjust flapper leveling screw 3 (the screw nearest
the nozzle).
8. Set the proportional band to 30 percent
REVERSE.
9. The controller output should be 0.62 ±0.02 bar (9
±0.25 psig) or 1.2 ±0.04 bar (18 ±0.5 psig). If not,
adjust flapper leveling screw 1 (the screw nearest
the nozzle).
10. Repeat steps 4 through 9 until the controller
output remains in tolerance without further leveling
screw adjustments.
11. If link 1 was disconnected, remove the tape and
reconnect link 1 to the input element.
12. Set the proportional band to 400 percent in the
desired controller action and replace the proportional
band indicator cover.
4195KA, KB, KC, and KS Controllers
RESET BELLOWS (VENTED)
PROPORTIONAL
BELLOWS
FLAPPER
NOZZLE
Figure 3-4. 4195KA Series Controller Schematic
PROPORTIONAL
BAND ADJUSTMENT
FEEDBACK
LINK
FEEDBACK
MOTION
DIRECT ACTION
QUADRANT
SUPPLY
PRESSURE
Principle of Operation for 4195KA
Series Controllers

Overall Operation

Refer to the schematic diagram in figure 3-4.
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. The action of the proportional
bellows counteracts the flapper movement that
resulted from the process pressure change and
backs the flapper away from the nozzle until
equilibrium is reached.
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.
The proportional band adjustment positions the
nozzle on the flapper. Increasing (widening) the
proportional band moves the nozzle to a position on
REVERSE ACTION
QUADRANT
FLAPPER PIVOT
INPUT
MOTION
FLAPPER DETAIL
OUTPUT PRESSURE
TO FINAL CONTROL
ELEMENT
RELAY
3-7