PH oddities
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Hello, we use Shangtai pH meters. Sodium hydroxide and sodium hypochlorite are used as the main agents to neutralize any excess chlorine that has not reacted. So far, several pH meters have been replaced, with one needing to be changed every 2–3 days, yet the readings remain inaccurate. It just worked when I replaced it to test the alkalinity, but after half a day the value didn’t drop. Testing with a pH strip shows around 5-6, while the pH meter indicates around 9. The deviation is too large. Because this value is used in the process to control the opening and closing of the valve. Could you help determine where the problem lies?
It needs to be calibrated; the electrodes are vulnerable components
Sodium hypochlorite redox reaction requires an ORP meter; pH meters have large measurement errors
The calibration has been done; all the manufacturers from Shangtai have been called over. I also replaced the Mettler electrodes, but it’s still the same.
Is it caused by crystals on the surface? Can an ORP meter solve this problem?
This post was last edited by Stone_HOTO on 2018-11-26 at 12:28. If it’s not a table-related issue, then one needs to consider the process conditions such as flow rate, temperature, pressure, etc., to see whether they are met, and whether the operation is intermittent
Is a flow cell used, or is it installed directly on the pipeline? It is necessary to ensure it remains fluid
We encountered a similar situation before as well; the main reason was that the operating conditions during measurement were not the same as those during design, which led to such deviations https://bbs.hcbbs.com/thread-1986195-1-1.html
It is normal for conventional pH electrodes to show deviations or even large errors when measuring such systems containing active chlorine. Such special process conditions require the use of a special pH electrode. All measurements related to brine and chlorinated brine in the chlor-alkali industry fall under this special category. For other systems containing sulfides, cyanides, and bromides as well, special consideration must be given to the choice of pH.
Using the new one, the measurement results are the same