PID Controller

pokemal

Member
Join Date
May 2009
Location
berlin
Posts
2
Hello;

I am trying to control DC Motor with PID and PLC.

I have already calculated the parameters (KP KD KI).

But I couldn't manage to design PID algorithm in PLC with KP KD KI. (Not Kc Ti Td)

Could you give some example about designing PID controller.


Thanks in advanced.
 
I think you need to tell us more about the load the motor is driving.
Also would be helpful to include motor RPM HP and other values.
Dan Bentler

Hi Dan;

First of all thanks for your quick reply.

I am driving 12 V dc motor with H-bridge. And also taking output from tachometer.

I will use analog input module with my PLC. So think I have instant speed value of dc motor.(via AIW0)

The problem which I am trying to solve is designing PID(with Kp Kd and Ki parameters)

My PID parameters are:
Kp: 2.16
Kd: 23
Ki: 0.0385

I have PWM blocks and I think I need VW102 value from this PID algorithm.(Please look at the attached image)

I hope I gave enough information which you will understand me.

Also sorry for my poor English:(

Thank you very much.

plc v.JPG
 
A trip in the 'way back' machine yields.....

http://www.plctalk.net/qanda/showpost.php?p=1286&postcount=8

I was going to say do a search for Peter Nachtwey and the topic PID but there are now 11 pages of Peter Ponders PID stuff to wade through and I am adding more. There should be an index. TMI.

How did you calculate the gains? They don't look right. Normally the integrator gain is much higher than the proportional gain which is much higher than the derivative gain IF you are using gains instead of time constants.

Your gains could only be valid if you didn't take into account the sample time when computing the Ki and Kd gains.

Bigger systems with longer time constants are easier for PLCs to control rather than small DC motors with fast time constants. You will find that it will be hard to control small DC motors well with a PLC because the time constants are often faster than the PLC scans and the sample jitter causes a lot of 'noise' on the feed back so it is impossible to use the derivative gain. You would be much better off getting a DSP or microcontroller evaluation system.
 

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