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Just got a new project, that requires among other, a heating zone control using 6 PID loops.

When it comes to temperature control, I prefer to use external dedicated temperature controllers because I faced some problems with PLC outputs response (not Unitronics brand) in the past.

However my customer wants everything to be controlled via HMI so I will use a V350 with IO-ATC8 expansion module and some digital I/O expansions.

My application is as described below:

6 K-type thermocouple as input and 6 solid state relays for current switching. I will use PWM function block and Transistor outputs to “talk” to the SSR’s.

I have set the cycle time to 1.5 second (Took the average of the recommended cycle time range that is given in PID tips topic in Unitronics help files)

The SP value (set-point) for each loop is linked to a preset MI so that the user can change its value at any time from the HMI.

My questions are the following:

Do I have to run PID Autotune process every time the user changes the SP value? (Detect change in linked MI value).

Do I have to write 6 different autotune codes for each loop?

Thanks in advance,


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Thanks for the reply.

It is a little bit confusing because in PID configuration topic of help file it's written that:

To enable PID, values must be provided for:

  • Set Point
  • Input Range:PV Low Limit & PV High Limit
  • Output Range:CV Low Limit & CV High Limit

These values are used to Auto-tune the loop.

So i thought that as set point is used as a parameter to Auto-tune the loop,when it changes i have to run Auto-tune again.

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