Vacuum is a physical phenomenon. It is a non-existent space state. Generally, it uses the change of some physical effect of gas at different pressures to measure the pressure. Widely used in scientific research and industrial production.

First, according to the vacuum scale method classification

(1) Absolute vacuum gauge: direct reading of gas pressure, its pressure response (scale) can be calculated by its own geometry or determined by the force measurement. The absolute vacuum gauge is accurate for all gases and is independent of the type of gas. U-type pound pressure gauges, compression vacuum gauges and thermal radiation vacuum gauges are among the absolute vacuum gauges.

(2) Relative vacuum gauge: The pressure is determined by the function of some gas pressures. It cannot be entered into the scale through simple calculations. It must be calibrated to scale. The relative vacuum gauge is generally composed of a gauge gauge (or gauge head) as a sensor and a gauge for control and indication. The reading is related to the type of gas. There are many types of relative vacuum gauges, such as heat conduction vacuum gauges and ionization vacuum gauges.

Second, according to vacuum gauge measurement principle classification

1. Direct measurement vacuum gauge (1) Static level vacuum gauge: The pressure is measured by using the difference in the liquid level at the two ends of the U-shaped tube.

(2) Elastic element vacuum gauge: The surface of the container connected to the vacuum is subjected to pressure to produce elastic deformation to measure the magnitude of the pressure value.

2. Indirect measurement vacuum gauge (1) Compression vacuum gauge: The principle is to apply Boyle's law on the basis of the U-shaped tube, that is to say, a certain amount of gas to be measured, after being isothermally compressed to increase the pressure, so as to use U-tube vacuum gauge measurement, then use the relationship between volume and pressure to calculate the measured pressure.

(2) Heat conduction vacuum gauge: It is made by using the principle that the gas heat conduction under pressure is related to pressure. Commonly used resistance vacuum gauge and thermocouple vacuum gauge.

(3) Thermal radiation vacuum gauge: The principle of using gas heat radiation and pressure under low pressure.

(4) Ionization vacuum gauge: The principle that the ion molecules are impacted and ionized by the charged particles when the gas molecules are under low pressure. Such as: hot cathode ionization vacuum gauge, cold cathode ionization vacuum gauge and radioactive ionization vacuum gauge and so on.

(5) Discharge tube indicator: The degree of vacuum is determined by the nature of gas discharge and the color associated with the discharge color and pressure. Generally, it can only be used as a qualitative measurement.

(6) Viscous Vacuum Gauge: The principle of external friction is the exchange of momentum between the gas and the vessel wall at low pressure. Such as diaphragm vacuum gauge and magnetic levitation rotor vacuum gauge.

(7) Field-induced microscopy: The pressure is calculated by the relationship between the time of adsorption and desorption and the pressure.

(8) Partial Pressure Vacuum Gauge: Measurement of mixed gas partial pressure using mass spectrometry. Commonly used quadrupole mass spectrometer, cyclotron mass spectrometer and radio frequency mass spectrometry