Sensor - The Electronic Nose Artificial Olfaction Technology - page 56

Fig. 2.15 Dew point meter

pH ¼ log H þ ½

pH System

A successful pH reading depends upon all components of the system being
operational. Problems with any one of the three: electrode, meter, or buffer will
give in poor readings.
Electrodes: A pH electrode consists of two half-cells; a demonstrating (Mea-
suring) electrode and a reference electrode. Most applications today use a com-
bination electrode with both half cells in one body. Over 90 % of pH measurement
problems are related to the improper use, storage or selection of electrodes.
Schematic of pH electrode is shown in Fig. 2.16 .
The mathematical expression for pH measurement is:

E ¼ E m E r

where:
E m

the electrode potential of the measuring electrode,

E r the electrode potential of the reference electrode.

Meters: A pH meter is a refined voltmeter capable of reading small millivolt
changes from the pH electrode system. The meter is infrequently the source of
problems for pH measurements. Today pH meters have temperature compensation
(either automatic or manual) to correct for variations in slope caused by changes in
temperature.

Microprocessor technology has created many new convenience