piddef resets pidcompute data.

[hareldvd]

Hi,

We have finally implemented a distillation control unit based on On a T100MD unit.
Using pid channel we control the heater.
Unfortunately when a liquid such as oil is heated there are different phases which require different pid values. I have the ability to identify the phase where I need to change pid definitions but doing so resets the current pid calculations and starts back from zero. This causes a major instability state in the controller.

I was told by my boss that on some controllers you can set manual value to pid so I could restore the pidcompute result and have next pidcompute use new P I D values. Is that possible on any Tri products?

[support]

It is not possible to execute the PIDDEF function without resetting the PID historical data.

To achieve what you want to do in the M-series PLC, you would have to  implement your own custom made PID function yourself using the TBASIC language. By means of a clock pulse you can periodically trigger a custom function that compare the feed back value to a set value and take the difference to apply to your own P, I and D multiplier.  You then need to use a DM variable to accumulate the integrator and also to compute the derivative  term based on the diffence between current value and previous value.   There should be text book that demonstrate how to implement PID using a Visual BASIC program on a PC and you can adapt that to TBASIC.