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ORP Probes foul and cause problems in etching process

We are a company who etch stainless steel with FeCl3. We are having problems with ORP monitoring. We have frequent breakdowns because of ORP going high/low. It is believed that during continuous use of these electrodes, some etchant sticks to these electrodes which gives us false reading because it is ORP of that stuck etchant and fresh etchant flowing across the probes. To some extent problem is solved each time when we clean those probes. I was wondering how we can solve this problem, so that we have to put down our machines less frequently and don't have much problems too. Any help will be appreciated.

Thanks in anticipation.

Vipul Goel
Process Engineer - Hutchinson, MN, USA
2003

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You probably need to look more at the physical setup than anything else. Anything you can do to improve flow around the electrodes will improve the situation, as well as making sure that the solution does not cool down at the point of measurement. Finally, don't use scratched electrodes.

James Totter, CEF
- Tallahassee, Florida
2003

Improved flow rate will greatly reduce scaling of probe. What I have done to reduce down time in cleaning of probes (ORP and pH) in my waste treatment was to install a loop and sample pump just for this loop. Then I mounted the probes onto the loop and calibrated to the range that I desired. Not only that the flow reduced the down time but the readings and stability I was looking for was easily obtained. Hope this will help.

Mike Crabtree
- Raleigh, N.C., U.S.A.
2003