Thermo Fisher Scientific CyberScan pH 1500 - Manual (Page 49)

Instruction Manual CyberScan pH1500
47
10.1 Measuring pH
To measure pH, the meter receives a millivolts signal from a glass
bulb electrode that is sensitive to hydrogen ions. Therefore the
potential developed at the glass bulb is directly related to the pH of
the solution.
The glass bulb electrode is paired with a reference electrode which
completes the electrical measuring circuit and provides a stable
reference point. These two electrodes can be separated or they can
be joined to create a combination electrode. The combination glass
electrode makes a single connection to the pH meter which converts
the electrodes millivolts output to pH unit, and displays the result.
This meter can also use a field effect transistor (FET) electrode for
measuring pH. This type of electrode employs an ion-sensitive solid
state membrane as part of a transistor to measure the hydrogen ion
concentration of a solution. The FET is paired with a reference
electrode and counter electrode that maintain a constant potential
while the FET responds to the sample.