Difference between vacuum gauge and ordinary pressure gauge

In fact, the vacuum gauge is a kind of pressure gauge.

There are several kinds of work principles.

Classification by vacuum gauge measurement principle

Directly measured vacuum gauge, which directly measures the force per unit area, has:

(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 to measure the magnitude of the pressure value.

Indirectly measured vacuum gauge, when the pressure is 10-1 Pa, the force acting on the surface of 1 cm 2 is only 10-5 N, 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. Vacuum gauges belonging to this category are:

(1) Compressed 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) Heat conduction vacuum gauge: It is made by the principle that the heat conduction of gas under low pressure is related to pressure. Commonly used are resistance vacuum gauges and thermocouple vacuum gauges.

(3) Thermal radiation vacuum gauge: The principle of thermal radiation of gas under low pressure is related to 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.Such as: hot cathode ionization vacuum gauge, cold cathode ionization vacuum gauge and radioactive ionization vacuum gauge.

(5) Discharge tube indicators:The degree of vacuum is determined by the nature of the gas discharge condition and the discharge color are related to pressure, generally only as a qualitative measurement.

(6) Viscous vacuum gauge: The principle of external friction is used to exchange the momentum of the gas and the vessel wall under low pressure. Such as diaphragm vacuum gauge and magnetic suspension rotor vacuum gauge.

(7) Field-induced microscopy:The pressure is calculated by the relationship between adsorption and 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 are quadrupole mass spectrometers, cyclotron mass spectrometers, and radio frequency mass spectrometers.

Vacuum gauges are generally used for negative pressure. Compared with ordinary pressure gauges, it is only the difference between the range of pneumatic pressure and the accuracy.

The measurement range of the vacuum pressure gauge is 0-1 atmosphere, and the ordinary pressure gauge is usually an amount of atmospheric pressure of 0-tens, several hundred or even more. The measured readings will be much more accurate when the range is selected.

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