...
What is measured as pH is logarithm taken from hydrogen ion concentration in moles per liter, mathematically expressed as following:
It describes the acidity or alkalinity of a solution, for example used in an industrial process. Lower case letter p stands for negative base ten logarithm ad the upper case letter H stands for element hydrogen
...
There are many ways to measure pH from a solution. One very common way is the color changes in chemical powders, like litmus strips used in elementary chemistry. In modern industrial applications, a pH probe is often used. This kind of probe contains two electrodes that generate voltage, which is proportional to pH of the solution in question.
One of the two electrodes is a measurement electrode constructed out of special glass in order to create ion selective barrier. This barrier hen screens out hydrogen ions from the large flock of ions otherwise present in the solution [1]. Reference electrode is designed in a way that it maintains a constant potential at any given temperature. When reference potential is compared to the potential of the pH electrode, a millivolt signal proportional to pH is created allowing for the measurement. [2]
Reference electrode is made using chemical solution that is neutral pH buffer solution that is allowed to exchange ions with the process solution through a porous separator, forming low resistance connection to the test liquid. This electrode creates a reference on which to compare potential readings from the measurement electrode. Reason for usage of wet chemical interface is that they produce less voltage across the interface of contact, allowing for more accurate measurements [1].
...