What is the working principle of a pH meter?
A pH meter uses an electrode system to measure a voltage associated with the sample’s acidity or alkalinity. The instrument converts that signal into a pH reading after calibration.
The sensing and reference electrodes
A typical glass pH electrode has a hydrated sensing surface that responds to the sample. Its electrical potential is compared with a reference electrode. Many probes combine both parts in one body. Probe designs differ, so the internal construction is not identical in every instrument.
From voltage to a pH reading
The meter relates electrode voltage to pH using calibration buffers with known values. Temperature, contamination and electrode condition can affect the measurement. A displayed number alone does not establish that the instrument was calibrated or used correctly.
Why calibration matters
Follow the procedure for your specific meter and electrode. Use suitable fresh buffers, rinse between solutions and allow the reading to stabilise. Hanna Instruments explains the calibration process.
Looking after the electrode
The glass bulb and reference junction need appropriate care. Follow the manufacturer’s instructions for cleaning and storage rather than assuming that plain water is a suitable storage solution. Read Hanna’s explanation of electrode hydration.
Measuring drinking water
Use equipment suited to the sample and record the measurement conditions. pH describes acidity or alkalinity; it is not a complete test of water quality. Read our drinking-water pH guide for context.
Technical reference: Hanna Instruments: how a pH meter works.