Principle Of Operation For 4195Kb And Kc Series Controllers; Overall Operation - Emerson Fisher KC Series Instruction Manual

4195KA, KB, KC, and KS Controllers
Calibration for the differential relief valve to
relieve on falling controller output pressure
1. Provide a means of measuring the controller
output pressure by connecting the controller output
to a pressure gauge (open-loop conditions must
exist). Do not apply supply pressure at this time.
2. Set the reset adjustment to 0.01 minutes per
repeat (wide open) and the rate adjustment (4195KC
Series only) to the OFF position.
3. For a controller with manual set point, move the
set point indicator to the mid-scale mark on the
process scale. For a controller with remote set point,
adjust the remote set point pressure until the set
point indicator is at the mid-scale mark on the
process scale.
4. Set the proportional band to 100 percent in either
the DIRECT or REVERSE action depending on the
application requirements.
5. Refer to figure 4-3 for the location of the
anti-reset windup differential relief valve. For the
differential relief valve to relieve on falling controller
output pressure, install the valve so the arrow on the
valve points up. To change the direction of the
arrow, loosen the two mounting screws, pull the
valve out, and reinstall the valve with the arrow
pointing up. Tighten the two mounting screws.
6. Provide a regulated supply pressure to the
controller. Do not exceed the normal operating
pressure in table 1-6.
Because of the high controller gain
with the reset adjustment at 0.01
minutes per repeat, the controller
output will not balance perfectly in the
following step. If the controller output
is stable for approximately 5 seconds,
it is adequately balanced.
7. Increase the process pressure (or vacuum for a
vacuum controller) to the controller until the
controller output pressure balances at 0.8 bar (12
psig) for a 0.2 to 1.0 bar (3 to 15 psig) output range
or 1.6 bar (24 psig) for a 0.4 to 2.0 bar (6 to 30 psig)
output range.
8. Turn the reset adjustment to the CLOSED
(4195KB Series) or OFF (4195KC Series) position.
9. Decrease the controller output pressure in small
steps [approximately 0.04 bar ( 0.5 psig)] by
changing the process pressure to the controller or by
4-10
Note
changing the controller set point. After each change
in controller process pressure or set point, the
controller output pressure should quickly change and
then stabilize at the new value.
10. Continue to change the controller output
pressure in 0.04 bar (0.5 psi) steps and check the
output pressure after each step to make sure it
stabilizes. At some point, the controller output will
start to ramp downward to 0 bar (0 psig) with no
further change to the controller input or set point.
Record the controller output pressure where this
ramping action begins because this is the point at
which the differential relief valve has relieved.
11. To obtain the differential relief valve differential
setting, calculate the difference between the original
controller output pressure in step 7 and the
controller output pressure recorded in step 10.
12. If the differential pressure calculated in step 11
is incorrect for the application, adjust the differential
pressure by turning the differential relief valve
adjustment screw, shown in figure 4-3. Turn the
screw clockwise to decrease the differential
pressure or counterclockwise to increase the
differential pressure. The differential relief valve is
set at the factory to relieve at approximately 0.4 bar
(5 psi) differential pressure.
13. Repeat steps 7 through 12 until the required
differential pressure is obtained.
Principle of Operation for 4195KB and
KC Series Controllers

Overall Operation

Refer to the schematic diagram in figure 4-5 for the
4195KB Series controllers, or to the schematic
diagram in figure 4-6 for the 4195KC Series
controllers.
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.
Instruction Manual
Form 5207
April 2007