As pH sensors experience aging over time, the pH calibration has to be periodically repeated. The time interval between calibrations cannot be specified. This depends on various factors:

  1. The Measured pH Value
  2. The Measured Liquid Solution
  3. The Temperature of the Measured Solution
  4. The Age of the Electrode Assembly
  5. The Accuracy Required by the User

The calibration interval can vary between hours, days, weeks or even months, and has to be established individually for each application and the expectations of the user. When working with unknown process liquids, it is advisable to initially re-calibrate as often as possible and keep records of results. Often changes in values such as the slope may indicate that a sensor requires more frequent calibration.

If no significant change of the calibration values is noticed, the frequency of the calibration may be extended over time.

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