pid

[khpp]

hello,

I am new to PID programming and I had a basic question. I am trying to control a valve such that I can control the pressure downstream of the valve. My input and setpoint variable are the pressure transducer measurement. However my PID should output a 0-5VDC signal to the valve which will in turn control the pressure downstream. I want to generate 0-5 VDC output according to the pressure reading.

How can this be done using PIDcontrols toolkit? Output of PID is the difference of the reference pressure and actual pressure reading so the DC voltage is generating according to the difference of the both the pressures instead of the reference pressure. Some guidance is needed.

[GerdW]

Hi khpp,

the PID from PID toolkit has several inputs:

- you can limit the output range to 0…5 (V) by setting the output limit cluster

- you can adapt the PID by it's PID parameters. Especially Kp is used to scale pressure difference to voltage signal change! You need to understand how the PID control works, then do some basic tuning steps to find the correct/suitable PID parameters!

Read wikipedia on PID control, key word is "Ziegler Nichols". The LabVIEW help also has some entries that explain the PID functions…

[chembo]

One of the inputs you can wire to the PID.vi is output range. It is a cluster with output high and output low.

You can wire in a cluster constant with output high = 5 and output low = 0.

Here is the link to the PID.vi help for LabVIEW 2012, but this is probably the same for all recent LabVIEW versions.