Instruction Manual
D103292X012
C1 Controllers and Transmitters
March 2017
20
Startup: Proportional-Plus-Reset Controllers (General Tuning Guidelines)
Calibrate the controller prior to this procedure.
1. Be sure that the supply pressure regulator is delivering the proper supply pressure to the controller.
2. Rotate the pressure setting knob to the desired set point.
3. Start with a reset setting of 0.05 minutes per repeat (m/r) for fast processes, and 0.5 m/r for slow processes.
4. Set the proportional band adjustment to 100 percent for fast processes (example: liquid pressure or liquid flow). For
a slow process (example: temperature), calculate the percentage from the equation below:
For a slow process, determine the initial proportional band setting in percent from the following equation:
2
AllowableOvershoot
PressureSpan
100%
+
P.B.
For example:
2
0.14bar
2.1bar
100%
^
13%
2
2psig
30psig
100%
^
13%
(
)
1.3 proportional band setting
5. Proportional Action:
Disturb the system by tapping the flapper lightly or change the set point a small amount and check for system cycling.
If the system does not cycle then lower the proportional band (raising the gain) and disturb the system again.
Continue this procedure until the system cycles. At that point, double the proportional band setting and begin tuning
the reset.
6. Reset Action:
Disturb the system. If the system does not cycle then speed up the reset and disturb the system again. Continue this
procedure until the system cycles. When the system cycles multiply the reset time setting by a factor of three (3) and
slow the reset down to the new value. The reset is now tuned.
This tuning procedure may be too conservative for some systems. The recommended proportional band and reset
setting should be checked for stability by introducing a disturbance and monitoring the process as previously
described. For some applications, tighter control may be desirable.
Differential Gap Controllers
This section describes the adjustments and procedures for calibration and startup. The adjustment locations are
shown in figure 4 unless otherwise specified. The output of each controller is checked at the factory before the
instrument is shipped.
To convert a differential gap controller to a proportional-only controller or vice versa, refer to the appropriate
procedure in the Maintenance section.
If the process pressure can be varied through all or part of the sensing element range or through the two desired
switching points, use the process pressure for calibration. If not, provide a pressure source to simulate the process
pressure range for calibration procedures.