pH Meters. pH meters are used to measure the acidity (or alkalinity) of a solution by measuring its hydrogen ion concentration or more strictly its hydrogen ion activity. pH is defined as -Log₁₀ of the hydrogen ion activity. A pH meter consists basically of two half cells, a measuring half-cell (e.g. a glass electrode) and a reference cell (e.g. a calomel electrode) joined by some form of electrolyte bridge. The pH is taken as a function of the potential across the electrodes that is measured by means of a high impedance input voltmeter.

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