pH Meter:

The instrumentation needed to perform potentiometric measurements involves a reference electrode, an indicator electrode and a high input-impedance mV (pH/pion) meter as depicted in Figure.

Ordinary laboratory volt meters cannot be used for the measurement of the emf of a glass electrode cells because of the high electrical resistance of glass electrode (typically 10-200 megaohms), special high-impedance voltmeter circuits are required, which draw 10-12 amperes or less from the circuit. The pH meter is a voltmeter but with several critical addition functions. Not just does it measure the potential across the pH-sensing and reference electrode system, but it also converts the potential difference measurement at a given temperature into pH terms, and it provides mechanisms to correct for the non-ideal behaviour of the electrode system. The operational amplifier not only serves as high-impedance voltmeter, but also provides stability and automatic operation through the use of the feed-back loop. The operational controls on a pH meter are best understood by reference to the operational manual provided by manufacture of individual instrument. Modern electronic techniques permit the production of simplified pH meter that measures pH with an accuracy of + 0.1 pH unit. The microprocessor equipped pH meters include a temperature probe to display temperature compensation, a memory for the pH values of standard buffers and a waiting period to permit draft before taking pH readings and built in diagnostics to alert for electronic malfunctions or defective electrodes. Along with pH meter we also require a reference electrode and a glass membrane electrode which acts as indicator electrode in pH measurement.