pH Sensors and Principles of Operation.doc

Gina Litz
GE 330
Sensor Report
pH Sensors and Principles of Operation
How They Work:
Understanding pH measurement
In the process world, pH is an important parameter to be
measured and controlled.

The pH of a solution indicates how acidic or basic (alkaline) it is.
The pH term translates the values of the hydrogen ion concentration
- which ordinarily ranges between about 1 and 10 x -14
gram-equivalents per litre - into numbers between 0 and 14.
On the pH scale a very acidic solution has a low pH value such
as 0, 1, or 2 (which corresponds to a large concentration of
hydrogen ions; 10 x 0, 10 x -1, or 10 x -2 gram-equivalents per litre)
while a very basic solution has a high pH value, such as
12, 13, or 14 which corresponds to a small number of hydrogen
ions (10 x -12, 10 x -13, or 10 x -14 gram-equivalents per litre).
A neutral solution such as water has a pH of approximately 7.
A pH measurement loop is made up of ponents, the
pH sensor, which includes a measuring electrode, a reference
electrode, and a temperature sensor; a preamplifier; and an
analyser or transmitter. A pH measurement loop is essentially
a battery where the positive terminal is the measuring electrode
and the negative terminal is the reference electrode. The measuring
electrode, which is sensitive to the hydrogen ion, develops a potential
(voltage) directly related to the hydrogen