A pH electrode is a passive device that detects a current generated from hydrogen ion
activity. This current
(which can be positive or negative)
is
very weak and cannot be
detected with a multimeter, or an analog to digital converter.
This weak electrical signal
can easily be disrupted and care should be taken to only use proper connectors and cables.
The current that is generated from the hydrogen ion activity is the reciprocal of that
activity and can be predicted using this equation:
Because a pH probe is a passive device it can pick up voltages that are transmitted
through the solution being measured. This will result in incorrect readings and will
slowly damage the pH probe over time. In this instance, proper isolation is required.
Where
R
is the ideal gas constant.
T
is the temperature in Kelvin.
F
is the Faraday constant.
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