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  for Metal Finishing since 1989
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pH sensor shock

I have been seeing ph sudden drops at random times in my process. The pH drops for no reason and slowly comes back to setpoint. On my trending screen you can see the pH as a flat line with occasional dips. Why? What could be causing this anolomy?

Harold Gonzalez
biotech - Thousand Oaks, California
2006

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I don't think you've given us enough to go by to make even a wild guess, Harold. Are you making acid additions? What is the source of the process you are monitoring? Are these dips confirmed with a portable meter or paper, or unconfirmed? Does it drop to a stable lower level on the dips like a loose wire? etc, etc.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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Hi Harold,

The most likely cause of the reading fluctuation is the design criteria of the pH electrode. Some electrodes can deal with high pH and others low pH, and still others are not that happy with buffered solutions or great temperature changes. So my suggestion is that you contact a reputable manufacturer (not supplier) of these electrodes (find them through your search engine) and explain the problem and allow them to suggest a suitable replacement.

If all else fails, the Litmus Test still works.

Have fun.

Tony Johnston
- Doncaster East, Melbourne, Australia
2006

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If the pH electrode is clean and calibrates OK, perhaps accurate, normal behavior. The pH is monitored & perhaps controlled because variation is possible. Look for irregular additions of chemicals, on/off rinsewater flows or large swings in temperature. A conductivity probe or a timer may be limiting water use in rinse tanks ˜ see '20 Ways to Cut Water Usage in Plating Shops' (www.finishing.com/library/mooney/20ways.html). When the flow valve opens, acidic rinsewater starts entering the pH adjust system. Or, a batch process with acidic drag-out may be occurring. The pH dips, then slowly rises as either the source is diluted by fresh water or a metering pump adds caustic to adjust the monitored pH.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006