Don't know the measurement principle of pH meter?
The pH meter is an important tool for measuring the pH of a solution, and is widely used in fields such as industry, electric power, agriculture, medicine, food, scientific research, and environmental protection. When using a pH meter, users need to have a certain understanding of its composition and measurement principle, so that it will be more convenient to use.
PH meter measurement principle
The principle and structure of an ordinary pH meter are shown in the figure above. The hydrogen ion activity of the liquid to be tested is used as the potential difference generated between the two electrodes, and the transmission signal is obtained through the transmitter to measure the pH value.
The electrode used as a reference is called a glass electrode, and looks similar to a glass test tube in appearance. However, the front end is thin film glass of several tens of μm made of special glass, and internal buffer and internal electrodes are built in. There is a glass film between the internal electrode and the liquid to be measured, which is basically insulated.
The electrode at the other end is called the comparison electrode (or reference electrode), which is similar in structure to the glass electrode, but there is a liquid junction at the front end, and the internal liquid contacts the liquid to be measured through the gap. There are various shapes of the liquid junction, including glass fiber shape, small hole shape, ceramic shape, casing shape, etc., which can be selected according to the specific application.
The impedance of the detection part is greater than 10MΩ due to the glass film, so the transmission part needs a higher impedance, which must reach more than 1GΩ, and high-insulation wires and terminals are also used between the amplifier and the electrodes.
The hydrogen ion activity of the measuring fluid creates a potential difference between the two sides of the thin-film glass of the glass electrode. The inner potential of the thin film glass of the glass electrode passes through the internal buffer solution and is derived through the inner electrode; while the outer potential of the liquid is derived through the inner electrode of the reference electrode through the liquid to be measured-reference electrode liquid junction-internal liquid. The potentials generated between the internal electrodes of the two electrodes and the internal liquid roughly cancel each other out, so the potentials on both sides of the film glass can be measured.
