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How does a pH meter/acidimeter work? An acidimeter operates on the principle of chemical galvanic cells. The electromotive force between the two electrodes of a galvanic cell is related not only to the properties of the electrodes themselves but also to the concentration of hydrogen ions in the solution; therefore, there is a corresponding relationship between the electromotive force and the concentration of hydrogen ions. And an acidimeter measures acidity using the concentration of hydrogen ions. Thanks to the new electrode design and solid-state circuit technology, good pH meters can now detect differences of 0.005 pH units. An acidimeter usually has a reference electrode and a glass electrode. The basic function of a reference electrode is to maintain a constant potential, serving as a benchmark for measuring various deviations from that potential. The silver-silver oxide electrode is a commonly used reference electrode for pH measurement; the function of a glass electrode is to respond to changes in the hydrogen ion activity of the solution being measured. By placing a pH-sensitive glass electrode and a reference electrode in the same solution, a galvanic cell is formed; the potential of this cell is the algebraic sum of the potentials of the glass electrode and the reference electrode, that is, E_cell = E_reference + E_glass. If the temperature remains constant, the potential of this battery changes as the pH of the solution being tested changes.