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When and How to Inspect, Clean and Calibrate pH Sensors
This paper will address
- Knowing when to do a pH sensor calibration versus a calibration check
- How to properly clean a pH sensor
- How to perform a pH sensor calibration
- A decision tree for step by step guidance
The phrase in the above title is actually incorrect in its sequence of wording. All pH readings are supposed to be taken and accepted only when the pH sensor is clean. After all, a contaminated pH sensor may yield an incorrect reading. So one must make sure the sensor is clean before doing a calibration. Once a pH sensor is installed in the process and operating, how do you determine when it is time to take the sensor out of the process and do a cleaning, or a calibration? Does one perform both a cleaning and a calibration or just a cleaning, or just a calibration, or does one just perform a calibration check in buffers or...?
This is something that can be quite confusing, especially when the operational practices and procedures documented by your company's Quality Control or Environmental Practices department may not be specific enough when they describe the procedure or the timing on when to conduct the pH calibration and maintenance. Inversely, the procedures may be too specific, detailing many more procedures and operations than are actually required.
In practical terms, users must develop their own maintenance and calibration schedule. This schedule is accomplished by taking the pH sensor out of the process after a set amount of time, perhaps after a day or two to perform a visual inspection of the sensor. If after inspection you find no debris or fouling on the electrode and reference surfaces with the naked eye, rinse the sensor off in distilled water and perform a buffer check.
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