# Zeigler Nichols PID tuning for a system with an integrator.

#### Ande

Joined Feb 3, 2017
44
I have been stuck on this homework problem for a while now. I am attempting to design a PID and a PI controller for the system shown in the attachment. The lecturer specifically requested that Ziegler Nichols tuning be used. The system however contains an integrator and because of this, the critical gain (proportional gain that would make it oscillate) is zero. Is there anyway of applying Zeigler Nichols tuning on a system with an integrator? I used a routh array to get the critical gain. Please advise.

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#### LvW

Joined Jun 13, 2013
1,187
Didnt you expect an integrating device as a part of a PID controller?

#### Ande

Joined Feb 3, 2017
44
Didnt you expect an integrating device as a part of a PID controller?
Please read the question properly before failed attempts at sarcasm. The plant contains an integrator, one of the requirements of ZN tuning is that you set the proportional gain to the point where the system oscillates, this cannot be done.

#### LvW

Joined Jun 13, 2013
1,187
I'm sorry if my answer sounded sarcastic. That was not my intention. I probably misunderstood something in the question - because of language problems

#### Ande

Joined Feb 3, 2017
44
I'm sorry if my answer sounded sarcastic. That was not my intention. I probably misunderstood something in the question - because of language problems
Okay, can you help then? I'm not sure how to go about solving this using ZN. Is it possible am I being thrown a curveballs?

#### MrAl

Joined Jun 17, 2014
7,978
I have been stuck on this homework problem for a while now. I am attempting to design a PID and a PI controller for the system shown in the attachment. The lecturer specifically requested that Ziegler Nichols tuning be used. The system however contains an integrator and because of this, the critical gain (proportional gain that would make it oscillate) is zero. Is there anyway of applying Zeigler Nichols tuning on a system with an integrator? I used a routh array to get the critical gain. Please advise.
Hello,

From what i have read it looks like the ZN method has very limited applicability and after all it is a heuristic method.
Maybe that means the answer is that you cant use it for that problem, or the editor made a mistake in the depiction of the plant transfer function.

For one, i can not find a critical gain, and secondly i can not find a frequency that makes the open loop phase shift 180 degrees (except for infinity which doesnt seem to help).

You could try reading around the web for any hints about how to handle cases that have plants that are not simply first order.