Re: [foxboro] pH control
- From: Terry Doucet <doucet427@xxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Mon, 15 Mar 2010 11:54:50 -0400
Robert,
"pH controller that seemed to be working over the years"
So did anything change - location of sensor, tank agitator, pH of input process
fluid (addition of a buffering agent), coating on sensor or target pH? Changes
in mixing are quite common that should be checked. Have you checked deadtime
for the pH measurement? DT should be reduced as much as possible by efficient
mixing, location of the sensor and efficient lime entry into the mixing vessel.
Is the lime feeding in clumps or is it nicely powdered and easily mixed?
Can you get repeatable pH with manual changes in lime feeder? Are you using
non-linear control in the PIDA?
Not much help, but perhaps things to check.
Terry
> From: Robert_Balmer@xxxxxxx
> To: foxboro@xxxxxxxxxxxxx
> Date: Mon, 15 Mar 2010 08:02:20 -0700
> Subject: [foxboro] pH control
>
> Ok I am going to try a cheat a little and see if those on the list have
> worked with tough pH control problems and may have some ideas that would
> speed up my response to a problem here on site.
> We have a pH controller that seemed to be working over the years that now the
> process engineers have learned to hate.
> We used a PIDA.
> The liquid volume changes frequently going into the vessel and we use a lime
> feeder to correct the pH. That feeder has at times presented it own
> opportunities, however in the past when it was working correctly operations
> seemed to be happy.
> Any ideas on perhaps a different control block or scheme would be helpful.
> Thanks
> Robert Balmer
> Senior Application Analyst/Programmer
> CCST
> Climax Molybdenum Co.
> 2598 Highway 61
> Fort Madison IA 52627
> (319) 463-2206
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