The three main components of the pH meter structure
1. A reference electrode;
2. A glass electrode whose potential depends on the pH of the surrounding solution;
3. A current meter that can measure small potential differences in circuits with high resistance.
The following are separate explanations of the main functions of each component:
1. The basic function of a reference electrode is to maintain a constant potential as a control for measuring various deviation potentials. The silver silver oxide electrode is currently the most commonly used reference electrode in pH.
2. The function of a glass electrode is to establish a potential difference that reacts to changes in the hydrogen ion activity of the measured solution. By placing the pH sensitive electrode and the reference electrode in the same solution, a primary cell is formed, whose potential is the algebraic sum of the potentials of the glass electrode and the reference electrode. E battery=E reference E glass. If the temperature is constant, the potential of this battery changes with the pH of the solution being tested. However, measuring the potential generated by the battery in a pH meter is difficult because its electromotive force is very small and the impedance of the circuit is very large, ranging from 1-100M Ω; Therefore, the signal must be amplified enough to drive a standard millivolt meter or milliampere meter.
3. The function of an ammeter is to amplify the potential of the primary battery several times, and the amplified signal is displayed through the ammeter. The degree of deflection of the ammeter pointer indicates the strength of the signal it pushes. For practical use, the pH ammeter dial is engraved with the corresponding pH value; The digital pH meter directly displays the pH value in numbers.
