What is the best algorithm to autotune a PID system which has heating (heater) and cooling (heat exchanger)? The output is a relay.

How do we tune the cooling part?

Thanks,

GH

 

There are lots of ways you can tune a control loop. The "best" tuning method is one which gives you the type of closed loop control that you want.

Heating/Cooling controls generally have different process responses depending on whether you want to heat or cool. Tuning is usually a compromise to ensure your loop remains stable unless you want to implement adaptive control tuning for heating & cooling

In my own experience I have rarely seen a DCS or PLC Autotune function ever work very well on simple loops, and on heating/cooling loops they usually have no chance. Others may beg to differ.

The best results usually come from a PID tuning package like Expertune's Loop Optimiser or RSTune where you do the bump testing and results analysis.

I would suggest you manually bump test your process for both heating & cooling & apply whatever tuning rules you are comfortable with.

Good luck.

Rob
www[.]lymac.co.nz