pH meter: A simple and speedy device to measure the acidity and alkalinity of a fluid. pH meters comprised of a special measuring probe (a glass electrode or, an ion-selective field-effect transistor (ISFET), in specialized cases), attached to an electronic meter that displays the decimal pH reading. pH is a measurable parameter between the values of 0 and 14, provided the concentration of the solution does not exceed 1M. Solutions with a pH<7 are acidic, whereas those with a pH>7 are alkaline.
The pH meter operates like a voltmeter. The pair of electrodes in the combinatorial set-up can measure small changes in voltage (also called potential difference) in the order of millivolts. The pH meter should be calibrated before each measurement using at least two standard buffer solutions of known pH values (typically around 4 and 7).