The most common pH electrode is the combination electrode, which contains both the reference and the measuring electrode
in one housing. This is a clear advantage for you, as a user. It's
easier to handle one combined electrode than two separate electrodes.
For some specific applications separate glass and reference electrodes are still used. They provide, if managed well, better accuracy for your pH measurement. However, in most cases combined electrodes are accurate enough and much more convenient to use.
The combination pH electrode consists
of a glass electrode concentrically surrounded by the reference
electrode, see the figure to the right. The shaft can be made of glass
or plastic. The pH sensitive part of the electrode is the glass tip or
the so-called glass membrane, at the bottom end of the electrode.
A good feature is the addition of a temperature sensor to the pH electrode. By housing the temperature sensor in the same body as the reference elements of the electrode, temperature compensated readings can easily be made with a single pH probe.
pH measurement is basically a measurement of the difference of the
electrical potentials between sides of glass in the glass membrane.
However, to measure an electrical potential you need to have a complete electrical circuit.
The electrical circuit is closed through the internal solutions of the
electrode and the measured media - and the pH meter. Even it's just one
potential you want to measure, there are different sources of potential and error involved in your pH measurement.
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