pH control using PIDE with autotune.

[briana banks]

Hi All

Is it wise to do pH control using PIDE with autotune?
If yes can someone show me a code snippet on how to do
the wiring in the function block?

cv-is the output of the dosage pump
pv-AI from the pH meter


Thanks

 

[Tom Jenkins]

You might want to consider an alternate algorithm or even a look-up table for this problem. Controlling pH is very non-linear, and PID may not work well or be easily tuned unless your operating range is fairly narrow.

 

[Greg Dake]

Sounds Fun

I agree with Tom on the non-linear(ness) of pH control.....In my past life I was "the pH guy" and spent countless hours trying to nail down pH control at the sugar plant I worked at. I have some great whitepapers somewhere written by "Dr. pH", a gentleman who works for ABB and dedicated his life to pH control. If anyone's interested you can PM me and I'll try to dig them out.

At any rate, I actually have a pH control application coming up at our plant. We will be controlling our sewer discharge pH with CO2. Looks like it will be pretty basic single loop control, one control valve and a sensor.....the control band is relatively wide 4.5-9.5, we'll see how it goes. I actually planned to use a Compact Logix PLC, I will give the PIDE block a shot. Briana, let me know how your installation goes. What are you trying to control the pH of?

Greg

***Quick Edit: Scratch the whitepaper offer, I just dug and realized I tossed the floppy they were on about a year ago.....I vouched I'd never do pH control again. However if you do a google search for "Don Spriggs" and pH, you will find several good articles.

 

[briana banks]

why the autotune doesnt run?

Hi
just trying to see if it works...

I press the start button after entering the parameters.
it says it is in progress but dont see any progress...
why?