5 | Measurement Basics
G 1501
12 / 37
B-H86.0.12.DB2-2.1
5.1.2
pH electrode
NOTE
Normally, so-called pH single-rod measuring chains are used. They include all neces-
sary components that are integrated in an electrode.
5.1.3
Design
Fig. 1: pH electrode
1.
Coaxial cable
2.
Reference electrode
3.
Measuring electrode
4.
Refill opening
5.
Electrolyte
6.
Internal buffer
7.
Diaphragm
8.
Glass membrane / source layer
The diaphragm, which establishes a connection between the electrolyte and the liquid
to be measured, can be designed in different ways. Clogging or soiling of the dia-
phragm is a frequent cause of a malfunctioning or sluggish electrode. Always handle
the glass membrane with extreme care. The so-called source layer forms there. This
is crucial for the measurement and must always be kept moist.
There are also electrodes with integrated temperature sensors.
5.1.4
Further information
A pH electrode is a wear part. If the signal is very slow or the required values are no
longer observed after careful cleaning and possible regeneration, the electrode must
be replaced. When using the electrodes, be aware that various substances in aqueous
solutions can corrode glass and that chemicals can produce a chemical reaction with
the KCl solution in the electrode, which can result in blockage of the diaphragm.
–
In solutions that contain proteins, such as for measurements in medical and bio-
logical applications, KCl can cause denaturation of the protein.
–
Coagulated paints
