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PID control

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I have only the second project in my praxis with PID control.

PLC: JZ-10-R16

PID: SP=3380 pulses


PVmax=5000 pulses







The principle of operation was taken from Unitronics sample project motorized valve action. Process value PV are frequency (100ms sample time). Calculated PID control value CV are sampled with actual feeddbeck from actuator CVR (4..20mA the range of units are from 50 for full close to 350 for full open).

If CVR-CV>H then actuator closing.

If CVR-CV<H then actutor opening. The H are hysteresis of 5 units.

Preblem is that the PV are close or reached the SP but CV are still growing and actuator (of course) starts flashing from min CVR to some position and there is no perturbance yet. Autotuning gives no result because it coud not end the process. I tried to change PID parmeters (kp. Ti, Td) but I get overruns and underruns faults from process, so the abouve parameters looks like optimal (especially when perturbance take an action).

What coud a I do to get smoother process control? May be Motorized actuator are very fast (about 3 sec.) and I misstake in fundamental choosing PLC and actuator?

Here I attached xls file with process log file.

Thanks in Advance.


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  • 3 weeks later...

Can you send your application and OPC server log, including CVp, CVi and CVd to support@unitronics.com. You can add in your application FB PID module Read Control Components, recommended with Factor 10 or 100, which will give you relevant values.

BTW - why you set CV range 50 - 350? Is the full opening time of thhe valve 35 seconds? Whay you don't want PID to close it fully and leave min value to 50?

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