PID Tuning / HND help

Hi,

I have a question in my Instrumentation & Control HND which is as follows:

Figure 3 shows the open-loop response of a process modelled by the parameters K = 0.75, T= 50 s and L = 20s.

Determine suitable PID controller settings for the process using the ‘open-loop response’ method.

I have looked though my course material and cannot find anything explaining the "open loop response" method.

If I Google it it comes up with lots about Open Loop control systems but this is not what i'm after. I have looked through my Bolton text book which has:

1) Reaction tuning
2) Ultimate Cycle tuning
3) Ziegler Nichols tuning

but not open-loop response. Is Open-loop response method simply manual tuning?! As its not part of a closed-loop system?

Hello. Just wondering if you managed to answer this question? I am having similar difficulty with a very similar assignment question. Any pointers? Thanks

@DLMUK, Are you sure the "OPEN LOOP METHOD" wasn't what was used to estimate K,T and L?
Are you sure you are reading the problem right.
I have never heard of an "open loop method" for calculating the closed loop controller gains and I have been at this for a long time. I use open loop control to compute the system parameters like K,T and L.

Once you have the K,T and L you need need to use the other 3 methods you listed.

The values you have for gain, time constant and dead time is sufficient to calculate PI gains. No derivative gain is needed in your example.
I would use POLE PLACEMENT or DIRECT SYNTHESIS to compute the controller gains.

Do a search for direct synthesis. You will find a pdf from the Colorado school of mines the formula for a FOPDT system.


@pshell, do you have the same instructor?

pshell said:

Hello. Just wondering if you managed to answer this question? I am having similar difficulty with a very similar assignment question. Any pointers? Thanks

Click to expand...

Has anyone managed to complete this question as I am also trying to figure out this question. Any help would be grateful.

Go to page 5/5 to get the IMC tuning
http://deltamotion.com/peter/Mathcad/FOPDT/Mathcad - FOPDT PI.pdf
I think the 'open loop method' is just a step change in the control output and measuring the response. Given you now have the gain, time constant and dead time there are many ways to tune the system but the method I show on page 5/5 is mathematically correct. ZN is just a guess.

This next file is the example I did for the controlguru.com website years ago.
http://deltamotion.com/peter/Mathcad/FOPDT/Mathcad - FOPDT.pdf
Pages 1 and 2 are the derivation of the formulas for the gain and time constant.
Pages 3-7 are an open loop and closed simulation.
You need to plug in your own numbers.

Peter Nachtwey said:

Go to page 5/5 to get the IMC tuning
http://deltamotion.com/peter/Mathcad/FOPDT/Mathcad - FOPDT PI.pdf
I think the 'open loop method' is just a step change in the control output and measuring the response. Given you now have the gain, time constant and dead time there are many ways to tune the system but the method I show on page 5/5 is mathematically correct. ZN is just a guess.

This next file is the example I did for the controlguru.com website years ago.
http://deltamotion.com/peter/Mathcad/FOPDT/Mathcad - FOPDT.pdf
Pages 1 and 2 are the derivation of the formulas for the gain and time constant.
Pages 3-7 are an open loop and closed simulation.
You need to plug in your own numbers.

Click to expand...

Thanks for the quick response Peter, I will input my own numbers and see what I get.
Your help is greatly appreciated Peter.