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274 UDC 3300 Controller Product Manual 4/00
11.2 Time, Position, or Current Proportional Simplex Control
Procedure
The procedure listed in Table 11-1 gives you the steps for manually tuning
a controller with Time, Position, or Current proportional simplex control.
Table 11-1 Manual Tuning Procedure for Simplex Control
Step Action
1
In Manual Mode, adjust the output to bring the PV (Process Variable) near
the desired value.
2
Set the Rate time to 0 minutes and set the Reset time to the maximum value
(50.00 minutes) or set repeats/min to the minimum value to minimize reset
action
If applicable, set the CYCLE TIME to 4 seconds and DEADBAND
to 0.5.
3
Increase GAIN (decrease PB) significantly. Try a factor of 10.
4
Adjust the local setpoint to equal PV and switch to Automatic control mode.
5
Increase the setpoint by 5 or 10% and observe the process variable
response.
6
If the PV oscillates, continue to Step 7. If it does not oscillate, return to the
original setpoint and increase GAIN (decrease PB) again by a factor of 2,
and repeat Step 5.
7
Compare the oscillations with the figure below:
Pattern A
Pattern B Pattern C
Amplitude
Time for one cycle
Process Variable
Time
20778
• If the oscillation matches pattern A, go to Step 8.
• If the oscillation matches pattern B, increase GAIN (decrease PB) by a
factor of 2 and repeat Steps 4 to 6.
• If the oscillation matches pattern C, decrease GAIN (increase PB) by a
factor of 0.8 and repeat Steps 4 to 6
The amplitude of the cycle is immaterial, but all of the elements of the loop
must be within the operating range (i.e., the valve must not go full open or
closed).
8
Record the current value of GAIN (or PB) and measure and record the value
of time for one completed oscillation of PV.
9
Select the proper set of formulas from Table 11-2. Use the values of Gain (or
PB) and time (in minutes) in the formulas to arrive at the controller’s tuning
parameters settings.