PH meter principle PH meter classification
The ph meter is also called the acidity meter. It is a commonly used instrument and equipment mainly used to precisely measure the pH value of the liquid. It can also measure the MV value of the ion electrode potential with the corresponding ion selective electrode. It is mainly used in chemical process, pharmaceutical industry, food technology and other fields.
pH meter principle
The most basic method is to determine the pH value of the solution by the potentiometric method. The principle of potentiometric pH measurement comes from the Nernst formula. If a hydrogen ion reversible electrode and a reference electrode are put into the solution, a primary battery is formed. Since the potential of the reference electrode in the primary battery is constant under certain conditions, the value of the electromotive force of the primary battery changes with the activity of hydrogen ions in the measured solution. Therefore, by measuring the electromotive force of the galvanic cell, the pH value in the solution can be calculated.
pH meter classification
According to the needs of production and life, people have scientifically researched and produced many types of pH meters.
1. According to the measurement accuracy
It can be divided into 0.2 level, 0.1 level, 0.01 level or higher precision.
2. According to the volume of the instrument
There are pen type (mini type), portable type, desktop type and online type for continuous monitoring and measurement.
3. According to the requirements of use
Pen type (miniature) and portable pH pH meters are generally used by inspectors to bring them to the site for inspection.
Components of a pH meter
The pH meter consists of three parts, simply put, it is composed of an electrode and an electric meter.
1) a reference electrode;
2) A glass electrode whose potential depends on the pH of the surrounding solution;
3) A galvanometer that measures tiny potential differences in a very resistive circuit.
Reference electrode:
The basic function of the reference electrode is to maintain a constant potential as a control for measuring various offset potentials. The silver-silver oxide electrode is currently the most commonly used reference electrode in pH.
Glass electrode:
The function of the glass electrode is to establish a potential difference that responds to changes in the hydrogen ion activity of the solution being measured. Put the pH-sensitive electrode and the reference electrode in the same solution to form a primary battery, and the potential of the battery is the algebraic sum of the potential 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 to be measured, and it is difficult to measure the potential generated by the battery in the pH meter because its electromotive force is very small and the circuit The impedance is very large, 1-100MΩ; therefore, the signal must be amplified enough to drive a standard millivoltmeter or milliamperemeter.
Ammeter:
The function of the ammeter is to amplify the potential of the primary battery several times, and the amplified signal is displayed by the ammeter, and the degree of deflection of the pointer of the ammeter indicates the strength of the signal it pushes. For the needs of use, the dial of the pH ammeter is engraved with a corresponding pH value; while the digital pH meter directly displays the pH value in numbers.
