The difference between vacuum gauge and ordinary pressure gauge

In fact, the vacuum gauge is a kind of pressure gauge. There are several working principles. According to the principle of vacuum gauge measurement, direct measurement vacuum gauge This type 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 between the two ends of the U-shaped tube. (2) Elastic element vacuum gauge: The elasticity is produced by the pressure on the surface of the container connected to the vacuum. In fact, the vacuum gauge is a kind of pressure gauge. There are several working principles. According to the measurement principle of vacuum gauge, directly measure the vacuum gauge. This kind of vacuum gauge directly measures the force per unit area. There are: (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 pressure is measured by the elastic deformation of the surface of the container connected to the vacuum under pressure. Indirect measurement of vacuum gauge When the pressure is 10-1Pa, the force acting on the surface of 1cm2 is only 10-5N. Obviously it is difficult to measure such a small force. However, the pressure change can be measured indirectly according to the change of the physical quantity related to the gas pressure at low pressure. The vacuum gauges that fall into this category are: (1) Compression vacuum gauge: The principle is to apply Boyle's law on the basis of a U-shaped tube, that is, a certain amount of gas to be measured is subjected to isothermal compression to increase the pressure. In order to use a U-tube vacuum gauge to measure, and then use the relationship between volume and pressure to calculate the measured 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: Use the principle of gas thermal radiation and pressure under low pressure. (4) Ionization vacuum gauge: Use the principle that gas molecules are ionized by energetic particles at low pressure, and the generated ion current changes with electricity. Such as: hot cathode ionization vacuum gauge, cold cathode ionization vacuum gauge and radioactive ionization vacuum gauge. (5) Discharge tube indicator: Use the gas discharge situation and the discharge color and pressure-related properties to determine the degree of vacuum, which can generally only be used as qualitative measurement. (6) Viscous vacuum gauge: Uses the momentum exchange between the gas and the container wall under low pressure, that is, the principle of external friction. Such as diaphragm vacuum gauge and magnetic levitation rotor vacuum gauge. (7) Field Microscope: Calculate pressure based on the relationship between adsorption and desorption time and pressure. (8) Partial pressure vacuum gauge: Use mass spectrometry to measure the partial pressure of mixed gases. Commonly used are quadrupole mass spectrometers, cyclotron mass spectrometers and radio frequency mass spectrometers. Vacuum gauges are generally used in places with negative pressure. Compared with ordinary pressure gauges, it is only the difference between the range and accuracy of air pressure. The measurement range of a vacuum pressure gauge is 0 to 1 atmosphere, while an ordinary pressure gauge is usually 0 to tens, hundreds or even greater atmospheric pressure. If the range is selected, the measured readings will be much more accurate.