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Problem:
Auto Tune "hangs up" during Auto Tune Sequence steps 1, 2, or 3 and never finishes.
Cause 1:
One degree C of temperature instability due to noise pickup will prevent Auto Tune from
completing successfully.
Solution 1:
Possible solutions to this problem are:
Improve sensor wiring, shielding, and grounding and re-tune the loop.
Remove process disturbances which prevent the temperature from stabilizing (step 3 of
the Auto Tune Sequence described above).
If the temperature cannot be stabilized to within one degree C then the loop must be
tuned manually as described beginning on page 4.5. In this case, it is further
recommended that the Rate term be forced to 0. This will prevent the temperature
instability from causing erratic PID output.
Cause 2:
The initial programmed PID Gain, Reset, and Rate values are inadequate.
Solution 2:
Set Rate to zero and select PID Gain and Reset values until the Temperature Controller
begins to move the temperature closer to the SetPoint. Auto Tune Optimization on page
4.4 describes the effect Gain and Reset have on the PID controller.
Problem:
Auto Tune causes the temperature to deviate too far from the SetPoint.
Cause:
Auto Tune must bump the output 10% in order to learn the process dynamics (step 4 of
the Auto Tune Sequence). This may be too great a change in some applications.
Solution:
Turn off Auto Tune at the maximum temperature deviation permitted by the application.
Auto Tune will then estimate the controller settings based on the information gathered up
to this point. The estimate will generally be inferior to the values which would have been
calculated had Auto Tune completed normally. If the estimated values are insufficient
then perform manual Auto Tune Optimization as described below.
LOOP TUNING
4.3
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