Transfer function of a PLC test rig

AI Thread Summary
The discussion focuses on developing a transfer function for a PLC test rig involving PID control of a pump based on tank levels. The user seeks assistance in calculating the transfer function to enhance their theoretical understanding. They mention the setup includes a tank significantly higher than others, which may impact the system dynamics. Previous attempts at manual tweaking have yielded acceptable responses, leading to interest in applying the Ziegler-Nichols tuning method for further experimentation. The conversation emphasizes the importance of both theoretical calculations and practical adjustments in control system design.
m250390
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Hi All,
I am currently building a test rig for a plc project I am doing, it involves PID control of a pump from the level of a tank. I have built my rig but now I am trying to get the transfer function of it so that I can work out some theory.

Any help on how to work out the transfer function please?

Schematic of set-up attached. I am not sure if it makes a difference but the tank on the right is about 3 metres higher than those two on the left.
 

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This probably won't answer your question. But if it were me, I would install the PID (make some educated guesses on your bands), start the system and use some ''trial and error" to "tweek" in the controller. I assume you haven't got any kind of control system other than manual now, so why not give it a try.
 
Thanks for your interest digoff. I have already tried tweaking the system manually and the response is quite acceptable. What I an trying to do is use Ziegler-Nichols ultimate sensitivity tuning method and experiment a bit with it.
 

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