Thermcraft XST-6-0-36-3V - Manual (Page 211)

Installation and Operation Handbook Tuning
2416 Controller 4-3
4.2.1 Typical automatic tuning cycle
Calculation of the cutback values
Low cutback and High cutback are values that restrict the amount of overshoot or undershoot
that occurs during large step changes in temperature (for example, under start-up conditions).
If either low cutback, or high cutback, is set to ‘
Auto’ the values are fixed at three times the
proportional band, and are not changed during automatic tuning.
Adaptive tune
Adaptive tuning is a background algorithm, which continuously monitors the error from
setpoint and analyses the control response during process disturbances. If the algorithm
recognises an oscillatory, or under-damped, response it recalculates the
Pb, ti and td
values.
Adaptive tune is triggered whenever the error from setpoint exceeds a trigger level. This
trigger level is set in the parameter ‘
drA.t’, which is found in the Autotune list. The value is
in display units. It is automatically set by the controller, but can also be manually
re-adjusted.
Adaptive tune should be used with:
1. Processes whose characteristics change as a result of changes in the load, or setpoint.
2. Processes that cannot tolerate the oscillation induced by a One-shot tune.
Adaptive tune should not be used:
1. Where the process is subjected to regular external disturbances that could mislead the
adaptive tuner.
2. On highly interactive multiloop applications. However, moderately interactive loops,
such as multi-zone extruders, should not give a problem.
Time
Setpoint
Temperature