Principle Of Operation For 4194Hb And Hc Controllers; Overall Operation - Emerson Fisher 4194HA Instruction Manual

Instruction Manual
D200156X012
3. For a controller with manual set point, move the set point indicator to 50 percent of the scale range. For a controller
with remote set point, adjust the remote set point pressure until the set point indicator is at 50 percent of the scale
range.
4. Adjust the proportional band to 100 percent in either the DIRECT or REVERSE action depending on the application
requirements.
5. Refer to figure 3‐1 for the location of the anti‐reset windup valve. For the anti‐reset windup valve to relieve on
falling controller output pressure, install the valve so the arrow on the valve points up. If you must change the
direction of the arrow, loosen the two mounting screws, pull the valve out, and reinstall with the arrow direction
reversed. Tighten the two mounting screws.
6. Turn on the supply pressure to the recommended value shown in table 1‐4.
Note
Because of the high controller gain with the reset adjustment at 0.01 minute 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 differential pressure input to the differential pressure unit until the controller output pressure balances
at 12 psig (for a 3 to 15 psig output range) or 24 psig (for a 6 to 30 psig output range).
8. Turn the reset adjustment to the CLOSED (4194HB controllers) or OFF (4194HC controllers) position.
9. Decrease the controller output pressure in small steps (approximately 0.5 psig) by changing the input to the
differential pressure unit or by changing the controller set point. After each change in differential pressure unit
input or set point, the controller output pressure should quickly change 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 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 anti‐reset windup valve has relieved.
11. To obtain the anti‐reset windup 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 by turning the
anti‐reset windup valve adjustment screw (figure 3‐1). Decrease the differential pressure by turning the screw
clockwise. Increase the differential pressure by turning the screw counterclockwise. The anti‐reset windup valve is
factory set at approximately 0.14 bar (5 psi) differential pressure.
13. Repeat steps 7 through 12 until the required differential pressure is obtained.

Principle of Operation for 4194HB and HC Controllers

Overall Operation

Refer to the schematic diagrams in figures 4‐2 and 4‐3 for the 4194HB controllers and the 4194HC controllers.
The differential pressure unit (input element) connects to the process indicator and to the flapper by connecting links.
As the process differential 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 resulting from the process differential pressure change and backs
the flapper away from the nozzle.
4194HA, HB, HC Controllers
July 2018
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