Overview
The maximum lifespan of a pH sensor depends on water quality and operating conditions—temperature, flow, fouling, pollution, aggressive media, and other stress factors. These vary from site to site and even from sample to sample, so remaining useful life must be judged from performance (calibration behavior and stability), not from a single fixed calendar interval alone.
Storage
A pH sensor ages even in storage. Reduce unnecessary stress by storing it in a temperature-controlled environment, keeping it upright, and using the KCl-filled protective caps supplied with the sensor so the reference junction and glass bulb stay properly conditioned.
Typical signs of aging
A common indicator is a gradual decrease in calibration slope over time, together with slower stabilization or more frequent need for adjustment—always evaluated against your process requirements.
Instrument limits and error messages
If calibration results fall outside the instrument’s mathematical acceptance window, the analyzer will typically show an error message and refuse implausible factors. That window is a built-in plausibility check, not a substitute for good reference technique.
When to replace the sensor
If a new calibration performed with best-practice methods (correct buffers, temperature matching, sufficient stabilization, clean sensor) does not bring slope and zero back into a usable range, the sensor has reached end of life and requires replacement.
Mathematical window
The following ideal values and acceptance windows are typical for the plausibility check described above (exact limits can depend on firmware and product line—use the message text and manual for your instrument as the final authority):
Slope: ideal 59.2 mV/pH; acceptable window 50.0 to 60.0 mV/pH.
Zero point (offset): ideal 0 mV; acceptable window ±58 mV.
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