V570 PID autotune issue

[Vidmas30]

Good morning,

 We have a v570 PLC running on site for about 6years, controlling el. actuator (steam-water) by set temperature. Something happened and it began to work very bad - tmperature is too low or too high. In case we don't have posibility t check this matter on site, we gave a password to PID parameter window and suggested to check if it's OK with P,I,D variables. So the matter is:

1. After they tried PID autotune it done about 10 cycles and calculated souch parameters P: -0.3%, I: -0.2%, D: 2s.  The control was not good. After repeated autotuning it calculated the same parameters. Question: why there are negative values? We suggested customer to tune PID manually. Then..

2. After some manual tuning it was pretty OK, but then some colegue pushed an autotune button again, they tried to stop it and now seems like PID block is hanged up - after reseting PLC, PID status shows autotune is running, but CV value is not changing. How to reset PID block?

Thank you!

[AlexUT]

Hello Vidmas,

After 6 year some elements of PID loop will have degradation.

PID FB is a piece of software, keeping all PID parameters in linked MIs and MBs, and in block of 32 MIs.

Once you run PID Autotune for the first time and satisfied how it works, you have to save PID parameters for feature reference.

If PID cannot work stable, in most of cases you have to check other PID loop elements.

I recommend you to check all equipment in PID loop - sensor, actuator, etc.

Do you use Analog, Digital, or Relay output for PID output (CV, or Control Value)?

You can completely clean  POD parameters by cleaning linked MIs, MBs, and block of 32 MIs.

Than you have to run PID Autotune again.

I hope this helps.