Why is the relative accuracy specifications for pH meters listed with units stated in terms of what an electrode measures?

Document ID

Document ID TE919

Version

Version 3.0

Status

Status Published

Published Date

Published Date 09/28/2018
Question
Why is the relative accuracy specifications for pH meters listed with units stated in terms of what an electrode measures?
Summary
Meter relative accuracy
Answer
The specifications of the meter are “relative” because they apply only to the quality of the electronics used within the meter itself. The relative accuracy is expressed in the measurement units because it affects the whole measurement range in the exact same way. But it is the accuracy of the meter’s electronics alone, and does not indicate or predict the accuracy of the entire measurement system.

The entire measurement system is the combination of the accuracy of the meter, accuracy of the sensor’s temperature electrode, accuracy of the sensor’s reference electrode, accuracy of the sensor’s active electrode, measurement conditions particular to a test (sample temperature, volume, stirring), accuracy of the pH buffers used in calibration and finally repeatability (standard error of precision).

The entire measurement system’s uncertainty is based on all these individual components. The meter is one of those components and contributes to the whole system’s uncertainty. However, the effect of the meter’s accuracy on the final measurement is almost negligible compared with the other effects.

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