Steady state criteria with PID Setpoint

[Cyndi]

I am trying to automate a thermal cycle test. Is there a way to add steady state criteria and start dwell time after steady state is reached to PID setpoint? Or does anyone have a better way of doing this?

[johnsold]

I do not have the PID toolkit so I cannot comment on specifics, but in general you have to define your steady state criteria. If your loop is tuned to allow some overshoot then you may have to detect that and wait until the operating temperature has remained within a specified tolerance above or below the setpoint for a time longer than the period (actually half-period) of the overshoot oscillation. Once your criteria are met, then start the dwell timer.

If you are using a state machine as the architecture for your program, then states could include Change Setpoint, Detect Steady State, Dwell, Get Next Setpoint, etc. This type of structure allows you to easily change the detection of steady state parameters without affecting other parts of the porgram.

Lyn
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