How are pH values measured?

pH is a potentiometric measurement where the electrode used produces an electrical signal which the pH meter converts to a pH reading. The signal produced and measured is a voltage and since voltage is a potential difference, two potentials are needed to make a measurement:

1. The sensing electrode provides a potential proportional to the logarithm of the hydrogen ion activity in the sample.
2. The reference electrode ideally provides a stable and consistent potential independent of the activity of the sample.

The potential difference between the reference and sensing electrode is measured by the meter and converted into a pH value.