Help with PID and VFD

Hello,

hello my school project is to control level control with a pumps which drived with a vfd i am using rslogix500 to do this
the problem is the SP is a level and the PV is a level too which mean that the Control value will be a level too my question is if this CV will be conected directly to the VFD after being scaled or something else.

any help or a small project exemple for this will be really apreciated

thanks,

Why do you think the CV must be a level?

It is just 0-100% of the maximum control "force" available. For your drive that might be 0 to 50Hz speed reference. You just need to scale the PID blocks CV and use that for your drives speed reference. The PID block in micrologix processors is scaled 0-16387 from memory, but it's been a while.

Zip up your program and let's see what you've done so far

Saffa said:

Why do you think the CV must be a level?

It is just 0-100% of the maximum control "force" available. For your drive that might be 0 to 50Hz speed reference. You just need to scale the PID blocks CV and use that for your drives speed reference. The PID block in micrologix processors is scaled 0-16387 from memory, but it's been a while.

Zip up your program and let's see what you've done so far

Click to expand...

Hi saffa thank you for your answer
this the program that ive just made

Scale your PV and SP the same (0-100%).

Do you want the VFD to run in a closed loop to vary the HZ so that the level is always as close as can be to SP? If so, you need to use the PID instruction, SP, PV and output.

Might also need some logic to detect over level (PID out of control) and minimum level to stop the pump from damaging itself upon low level.