pH sensors

Electronic pHi meters consist of an electrolytic cell in which an electric current is created due to the hydrogen cations completing the circuit

The pH measurement originates in the electrode system. This system consists of a pH sensor, pH Half Cell, whose voltage varies proportionately to the hydrogen ion activity of the solution, and a reference electrode, Reference Half Cell, which provides a stable and constant reference voltage.

The pH electrode consists of a thin membrane of Hydrogen sensitive glass blown on the end of an inert glass tube. This tube is filled with an electrolyte, and the signal is carried through Ag/AgCl wire. This is a pH Half Cell. A similar system, but without using a Hydrogen sensitive glass, is used as a reference. A small filter (diaphragm) connects this tube to the external liquid. This system is called a Reference Half Cell.

The meter measures the difference between the pH Half Cell and the Reference Half Cell in Millivolts DC. This millivolt reading is read by the unit and displayed in either mV or pH units.