The pH measuring circuit consists of a reference electrode and a glass
electrode which are both immersed in the same solution. The active
measuring part is the pH sensitive glass electrode.
So, why do you need an electrode having a reference function?
pH measurement is a potentiometric measurement, a measurement of an
electrical potential. To measure an electrical potential you need to
have a complete measurement circuit.
For your pH measurement, it means that you need to electrically connect to the measuring medium.
Why not only use an electric wiring to connect to the measured solution? You learned from the glass electrode that to electrically connect to the internal buffer you could use a silver wire.
you measure pH you want to be able to measure a lot of different media,
with varying conditions and varying pH levels. Far away from a stable
buffer. A silver wire as a reference will give you an unstable behavior
with variable potential, and as a result a useless pH value.
The function of the reference sensor is to provide a constant potential regardless of the composition of the solution it is placed in.
To provide an accurate pH measurement, the reference must have a constant and stable potential. Any deviation in its potential will cause the overall potential to change, thereby causing an error in the pH reading.
Learn more about the reference electrode design.
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