pH Meter Working Principle
The pH meter is an important tool for measuring and reacting the pH of the solution, and the pH electrode can realize the function of detecting pH value and output signal by supporting the pH meter. There are various models and products of pH meters. The display mode is also divided into two options: pointer display and digital display. However, no matter how the type of pH meter changes, its working principle is the same. The main body of the pH meter is a precision potentiometer. A pH meter consists of a reference electrode, a glass electrode and itself.
pH meter components
1. A reference electrode. The basic function of the reference electrode is to maintain a constant potential and use it as a control for measuring various deviation potentials. The silver-silver oxide electrode is a commonly used reference electrode in pH meters.
2. A glass electrode. Its potential depends on the pH of the surrounding solution. The function of the glass electrode is to establish a potential difference in response to changes in the hydrogen ion activity of the measured solution. If the pH-sensitive electrode and the reference electrode are placed in the same solution, a galvanic cell is formed. The potential of the battery is the algebraic sum of the potentials of the glass electrode and the reference electrode, that is, E battery E reference + E glass. If the temperature is constant, the potential of the battery changes with the pH of the solution to be tested. However, it is difficult to measure the potential generated by the battery in the pH electrode, because the electromotive force is very small, and the impedance of the circuit is very large 1-100MQ. Therefore, the signal must be amplified to make it sufficient to drive a standard millivolt meter or milliamp meter.
3. A pH meter. It can measure tiny potential differences in circuits with extremely high resistance. The function of the pH meter is to amplify the potential of the primary battery several times. The amplified signal will be displayed by the electric meter, and the degree of deflection of the pointer of the electric meter indicates the strength of the signal it drives. For operation needs, the dial of the pH meter is engraved with the corresponding pH value, and the digital pH meter directly displays the pH value in numbers.
How does a pH meter work?
The pH meter uses the potentiometric method to measure the pH of the solution. Therefore, the working method of the pH meter can measure the electromotive force of the battery in addition to the pH value of the solution. PH is the activity of hydrogen ions in a substance, and pH is the negative number of the logarithm of the concentration of hydrogen ions.
The main measuring parts are the glass electrode and the reference electrode. The glass electrode is sensitive to pH, while the potential of the reference electrode is stable. Placing the two electrodes of the PH meter into the same solution will jointly form a galvanic cell. The potential of the galvanic cell is the algebraic sum of the potentials of the glass electrode and the reference electrode. The pH value detected by the electrode must be sent to the pH meter, which can store, display the data and inform the rest of the system. After adjusting the pH value, it is detected by the pH electrode again, and then the pH meter can compare and readjust the data.
The reference electrode potential of the pH electrode is stable. When the temperature remains stable, the potential change of the galvanic cell composed of the solution and the electrode is only related to the potential of the glass electrode. The potential of the glass electrode depends on the pH value of the solution to be measured, so only by measuring the change of the potential, the pH value of the pH solution can be obtained.