Transfer function of a PLC test rig

[m250390]

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.

 

[dlgoff]

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.

 

[m250390]

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.