Cascading PID Loop Tuning

[Chado613]

Just curious to see what are some of the more favorable methods?

I have never used one before and will be commissioning one in the near future.

Is it better to tune the master first? slave first?
Can autotune be used? (Programming with RSlogix 5000)
Any feedback would be greatly appreciated.

Thanks

 

[kdcui]

Hi Chado,

Check out this link, it explains a procedure for tuning a Cascade loop:
http://www.controlguru.com/2007/090207.html.

You will want to tune your Inner / Secondary / Slave loop first, this is because the inner loop is your "early warning" and any disturbances in inner loop impact the process variable of the outer loop.

If you tune your outer loop first, then it will not be tuned correctly after you tune your inner loop.

If you tune one loop at a time you can use software. I actually have Control Station's LoopPro Tuner and you can use this to look at both Manual mode / Open loop and Setpoint driven data, although you can manually calculate tuning parameters in Open Loop. However you have to do each loop one at a time (two bump tests are required) and not both at the same time.

I haven't used Autotune however.

At the very least check out the link and follow the procedure there. Elsewhere on the site there are IMC derived tuning correlations you can use to calculate tuning parameters. Here is the page for Non-Integrating processes (90% of the time). Here is the link for Integrating processes.

 

[Chado613]

Thank you kdcui

That was most helpful

 

[kdcui]

Here is a Tuning Guide also by the guys at Control Guru (via Control Station). Is sums up the rather large amount of content nicely.

 

[Chado613]

Thanks once again!