Thermcraft XST-2-0-12-1V1-E28, Instruction Manual

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3200 Series User Manual
Part No HA028651 Issue 11.0 July-12 67
11.3.8 Manual Tuning
If for any reason automatic tuning gives unsatisfactory results, you can tune the controller manually. There are a number
of standard methods for manual tuning. The one described here is the Ziegler-Nichols method.
Adjust the setpoint to its normal running conditions (it is assumed this will be above the PV so that heat only is applied)
Set the Integral Time ‘TI’ and the Derivative Time ‘TD’ to ‘OFF’.
Set High Cutback ‘CBHI’ and Low Cutback ‘CBLO’ to ‘Auto’.
Ignore the fact that the PV may not settle precisely at the setpoint.
If the PV is stable, reduce the proportional band so that the PV just starts to oscillate. Allow enough time between each
adjustment for the loop to stabilise. Make a note of the proportional band value ‘PB’ and the period of oscillation ‘T’. If
PV is already oscillating measure the period of oscillation ‘T’, then increase the proportional band until it just stops
oscillating. Make a note of the value of the proportional band at this point.
Set the proportional band, integral time and derivative time parameter values according to the calculations given in the
table below:-
Type of control Proportional band (PB) Integral time (TI) seconds Derivative time (TD) seconds
Proportional only 2xPB OFF OFF
P + I control 2.2xPB 0.8xT OFF
P + I + D control 1.7xPB 0.5xT 0.12xT
11.3.9 Manually Setting Relative Cool Gain
If the controller is fitted with a cool channel this should be enabled before the PID values calculated from the table above
are entered.
Observe the oscillation waveform and adjust R2G until a symmetrical waveform is observed.
Then enter the values from the table above.
Temperature
Time
Setpoint
T
R2G is correct
R2G is too large
R2G is too small