PID parameters

I have a system that has 2 position encoders (4 to 20 ma), 2 proportionnal valves. The system is used for position indexation.

Example 100% position desired : both indexers should move from position 0 to 100% at the same time.

One indexer is the master the other is the slave. The setpoints will be direct values such as 100,50 and 0% .

Does anybody know how I can figure out the values for (P,I,D) ?

Do you have a motion controller or are you trying to accomplish in a PLC? A dedicated controller will save you a lot of grief. You will also need to provide more specifics on your system such a cylinder sizes, pressures, valve sizes, load. You also need to consider what type of proportional valve you have becasue these are definately NOT created equal

I would recommend www.deltacompsys.com
An RMC 70 would work for this application.

There are so many variables involved here that calculating the PID is tough (although I'm sure some here will give you some advice). The systems I have worked on were tuned with basically educated trial and error.

Start out with basic values for PID, make a move, watch a graph of the results, make a change, make a move etc....

Please note I have no affiliation with Delta and an just recommending them because of past positive experience. There are other options.

There is no motion controller we are doing the loop through a Texas Instrument PLC TI505

Trying to do this in the PLC, while not impossible, is IMO not a good option. I STRONGLY recommend buying a motion controller

There is a reason that manufacturers use motion controllers and PLC manufacturers build motion cards.

I am afraid that if you are intent on using the PLC I can't help you much.

Karivelm, Are you wanting to setup a pid loop? I have setup pid loops in 505 softshop. I recommend reading the manual first. http://www.fast-soft.com/documents/manual-ws505.pdf Once you have read the manual I will try and help with any questions you have.

karivelm said:

There is no motion controller we are doing the loop through a Texas Instrument PLC TI505

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Allscott is right about using the RMC75. It has auto tuning and a means of graphing the postions and errors between the two axes so you know how well the system is working. If you do this project using a PLC for control you will not have auto tuning,graphs, fast deterministic update times, synchronized motion profiles, feed fowards, error logs etc.

I recommend that you check if the TI505 can communicate to the motion controller using Profibus DP. If it can then you can still use a motion controller.

Does anybody know how I can figure out the values for (P,I,D) ?

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Yes, you should do a search for advanced control on this forum. However, you should know that there is some 'homework' involved. It would be a lot easier to use the auto tuning or to use the graphs to minimize the sum of squared error between the feedback and the set point.

Call MCS Servo or Engrenage for info on the RMC motion controllers and training.

I am the president of Delta Computer Systems, Inc. the manufacturer of the RMC70 series of controllers. I am also working on an article right now for the Fluid Power Journal on gearing, synchronizing and camming. I think it will be released early next year.