1. Classified By Vacuum Calibration Method
(1) Absolute vacuum gauge: directly read the gas pressure. Its pressure response (scale) can be calculated by its own geometry or determined by the measuring force. Absolute vacuum gauges are accurate for all gases. U-type pound gauges, compression gauges and thermal radiation gauges are all belongs to the absolute vacuum gauges.
(2) Relative vacuum gauge: The pressure is measured by the amount that related to gas pressure. It cannot be scaled by simple calculation and must be calibrated to scale. A relative vacuum gauge generally consists of a vacuum gauge tube (or gauge head) that works as a sensor and a measurer that use 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.
2. Classification By Vacuum Gauge Measurement Principle
2.1. Direct measurement vacuum gauge
This kind of vacuum gauge directly measures the force per unit area, including:
(1) Static liquid level vacuum gauge: The pressure is measured by the liquid level difference at both 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 generate elastic deformation. Magnitude of the pressure value is measured by the elastic deformation.
2.2. Indirect measurement vacuum gauge
When the pressure is 10-1Pa, the force acting on the surface of 1 cm2 is only 10-5N, and it is obviously difficult to measure such a small force. However, the change in pressure can be measured indirectly based on changes in physical quantities associated with gas pressure at low pressure. This kind of vacuum gauge including:
(1) Compression vacuum gauge: The principle is to apply Boyle's law on the basis of the U-tube, that is, a certain amount of gas to be tested is subjected to isothermal compression to increase the pressure, so as to be measured by a U-tube vacuum gauge. Then calculate the measured pressure using the relationship between volume and pressure.
(2) Thermal conduction vacuum gauge: It is made by the principle that the heat conduction of gas under low pressure is related to pressure. Commonly used thermal conduction vacuum gauges are resistance vacuum gauges and thermocouple vacuum gauges.
(3) Thermal radiation vacuum gauge: Using the principle of heat radiation and pressure.
(4) Ionization vacuum gauge: The principle that the gas molecules are impacted and ionized by the charged particles under low pressure, and the generated ion current changes with the electric power. Ionization vacuum gauges include hot cathode ionization vacuum gauge, cold cathode ionization vacuum gauge, radioactive ionization vacuum gauge and so on.
(5) Discharge tube indicator: The degree of vacuum is measured by the gas discharge condition and the nature of the discharge color and pressure, and generally can only be used as a qualitative measurement.
(6) Viscous vacuum gauge: The principle of external friction is used to measure the pressure. Including diaphragm vacuum gauge and magnetic suspension rotor vacuum gauge.
(7) Field-induced microscopy: The pressure is calculated by the relationship between adsorption & desorption time and pressure.
(8) Partial pressure vacuum gauge: The mass spectrometry technique is used to measure the partial pressure of the mixed gas. Commonly used gauges are quadrupole mass spectrometers, cyclotron mass spectrometers, and radio frequency mass spectrometers.