PID with heating and cooling output (Re-post)


Thread Starter


Thanks to those who had contributed to my earlier post!

This is microcontroller based project. So I have to come out with an algorithm for heating/cooling with autotune capability. It is something like commercial PID controller which accepts temperature input and using primary relay output for heating and secondary for cooling.

In this project, cooling is by heat exchanger. As pointed out, guard band is needed but should it be for the cooling part alone. Meaning if temperature hit, for example, 2% above SV then cooling activated to bring the temperature down?

I think guard band in this application also acts as a cooling since in this non ideal world heat will be loss but in a slower manner.

How do we use Z-N algorithm for autotune the heating/cooling? Can we get Ku and Pu? If yes, Ku and Pu are for the heating or cooling part?

How can we autotune the controller once for heating or cooling? possible? or do we need to run autotune separately?

Do you guys know how the heating/cooling work in commercial PID controller? How the code/algorithm like to switch from heating (primary) to cooling(secondary) or the other way round? In other words, what is the protocol?

Sorry to ask so many questions because I am very new in this field.

Thanks in advance!