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

12. If the differential pressure calculated in step 11 is
incorrect for the application, adjust the differential
pressure by turning the differential relief valve adjust-
ment screw shown in figure 4–3. Turn the screw clock-
wise to decrease the differential pressure or counter-
clockwise to increase the differential pressure. The
differential relief valve is set at the factory to relieve at
approximately 5 psi (0.4 bar) differential pressure.
13. Repeat steps 7 through 12 until the required dif-
ferential pressure is obtained.
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 pres-
sure gauge (open-loop conditions must exist). Do not
apply supply pressure at this time.
2. Set the reset adjustment to 0.01 minutes per re-
peat (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 control-
ler. 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 bal-
ance perfectly in the following step. If
the controller output is stable for
approximately 5 seconds, it is adequate-
ly balanced.
7. Increase the process pressure (or vacuum for a
vacuum controller) to the controller until the controller
output pressure balances at 12 psig (0.8 bar) for a 3 to
15 psig (0.2 to 1.0 bar) output range or 24 psig (1.6
bar) for a 6 to 30 psig (0.4 to 2.0 bar) output range.
Note
4195KA, KB, and KC Series
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 0.5 psig (0.04 bar)) by changing
the process pressure to the controller or by 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 0.5 psi (0.04 bar) steps and check the output pres-
sure after each step to make sure it stabilizes. At
some point, the controller output will start to ramp
downward to 0 psig with no further change to the con-
troller 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 adjust-
ment 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 re-
lieve at approximately 5 psi (0.4 bar) differential pres-
sure.
13. Repeat steps 7 through 12 until the required dif-
ferential 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 dia-
gram 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.
Pressure in the reset bellows opposes the action of
the proportional bellows and slowly moves the flapper
4–9