PID Autotuning logic for use in RSLogix5000 and 500?

I tried searching the site, but there doesn't seem to be a lot of info about breaking down autotuning for ladder logic. I know Omron and that have built in autotuning, but i'm trying to find some kind of logic i can put into my programs to do the tuning. We have a big problem with tuning it at the plant here then sending it to our customers and them complaining the tuning isn't working very well for them. We don't want to have to travel for every unit we send out. If anyone can point me in the right direction in finding something like this or if you actually have something like this, it would be greatly appreciated.

Thanks.

See AB technote 41178

Send me your email I got some info that can help you.

william

TWS said:

See AB technote 41178

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that technote covers PIDE which is only available in RS5000 and only if you have the pro activation, poor guys like me only have the standard .

www.controlguru.com.

Lots of information that can help you understand what needs to be done.

the idea of putting a section of "home brew" auto-tuning code into the PLC has been tried before ... you can search the forum for my name (and that of my distinguished colleague Peter Nachtwey) for a thread where we discussed the idea at some lenth ...

if you'd like to discuss this by phone, feel free to give me a call ... I have more time to talk this week than I do to type - but I'll be glad to tell you what I ran into as I tackled a project EXACTLY like the one you're describing ... short story: I got it to work - but collecting the data in a proper format was the biggest headache ... without good data, you won't get good tuning ... it's hard (impossible?) to get the onsite operators to set up the test and collect the data properly ... if you've got a handle on how to get that part taken care of, then you might stand a fighting chance ... the rest is just mathematically crunching the data ...

quick question for you ... how do you currently do the tuning? ... Ziegler-Nichols? ... seat of the pants? ... etc.? ...

big picture idea: if you have a RELIABLE and SYSTEMATIC method for doing the tuning "by hand" then automating that procedure might be possible (after you get the "good" data of course) ... but if you don't have such a procedure, then the project becomes much more challenging ...

I just realized that the thread that I mentioned earlier was posted on another forum ... here is a link to it if you're interested in following up ...

http://forums.mrplc.com/index.php?s=&showtopic=9017&view=findpost&p=39939

also ... if you're not already familiar with RSTune (also known as ExperTune) then you might want to take a look at the following post too ... the part about collecting the data should be interesting ...

http://www.plctalk.net/qanda/showthread.php?postid=84553#post84553

good luck with your project ... please let us know how it turns out ...

Thanks to you guys for sending some answers. So no one has the actual ladder logic they are willing to share then? Fine, make me work... Right now we pretty much do the tuning "by the seat of your pants". I'm pretty new to the who PLC thing but my coworker knows some things. Our boss wants us to find something to do this auto tuning to result in basically the customer hitting a button and the PID will tune itself. He said we should start by calling Omron and others and ask how they do their patented autotuning. I wonder how long they will laugh at me until they hang up the phone. Judging by the lack of success I have been reading in multiple message boards, this seems like an impossible task. Autotuning software is out of the question for this company. We do heating and cooling process control units using the PID loops mostly on temperature control valves. I guess I will have to do some more research on this.

instant replay from my first post ...

if you'd like to discuss this by phone, feel free to give me a call ... I have more time to talk this week than I do to type - but I'll be glad to tell you what I ran into as I tackled a project EXACTLY like the one you're describing ...

Click to expand...

going further, since I was working for a systems integrator when I wrote the code, then technically the code belongs to him - not to me ... that being the case, I can't just post it on an open public forum ... I also cannot give you (or even sell you) a copy ...

on the other hand, I can (and am perfectly willing) to tell you how I went about the process, and offer you some guidance on how to proceed ... I'll do that for free as long as it's just "talking" ... fortunately (for me), I don't have time to type it all up - but (once again) please feel free to give me a call ...

Dave19711 said:

Thanks to you guys for sending some answers. So no one has the actual ladder logic they are willing to share then?

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You under esitmate the complexity of writing a auto tuning software.

Our boss wants us to find something to do this auto tuning to result in basically the customer hitting a button and the PID will tune itself.

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Nice goal. Your boss also under estimates the what it takes to go through an auto tuning procedure. As Ron said, it must be done right.

He said we should start by calling Omron and others and ask how they do their patented autotuning.

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Patented, what a joke. It is all in books or on the web. People have beeing doing auto tuning for years.

I wonder how long they will laugh at me until they hang up the phone. Judging by the lack of success I have been reading in multiple message boards, this seems like an impossible task.

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No, auto tuning takes a little math. A little too much for a PLC. You haven't searched this forum as Ron said.

Autotuning software is out of the question for this company. We do heating and cooling process control units using the PID loops mostly on temperature control valves. I guess I will have to do some more research on this.

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Auto tuning is a misnomer. I don't see anything auto about changing the control output in manual mode. The control output must be changed by significant amounts. The temperature must be allowed to approach becoming stable or steady state and then the control output should be changed back. The PV must be recored at regular intervals that are ten times faster than the plant time constant. 1 second intervals make the calculations easy. The plant model must be calculated ( estimated ) using system identification techniques. The control guru site shows you how look at a graph and do a best guess. That is very automatic. The plant model can be estimated use a optimizing algorithm which is actually a minimizing algorithm that minimizes the error between the PV and EV ( estimated value ). Next you need to pick the desired response. Do you want the settling time to be in 5 minutes or 10 minutes and how much overshoot are you willing to have. You chose your response and the computer will calcuate the gains for you. Chosing the response is not an automatic thing either.

'Auto tuning' is lots of 'fun' but once you do it once it is easy and you can keep your system tuned and tune the next one faster. It sure beats tweaking gains and drinking coffee waiting for the results.

Your boss is cheap.

widelto said:

Send me your email I got some info that can help you.

william

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Hello William

Please help me out...tips and tricks of PID tunning
I want to tune few temp and pressure control loops in Rslogix 5000, I have license for ladder instructions only. (Studio 5000 mini edition). If you can guide me this regards will help me a lot.

-Manasi