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  • Classification Of Vacuum Gauges
    May 30, 2018

    There are many types of vacuum gauges. For the convenience of research and use, reasonable classification is very important. The classification methods are different from each other. The following are two commonly used classification methods:

    1. Classification according to the scale method of vacuum gauge

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

    (2) Relative vacuum gauge: the pressure is determined by the amount of function relation to the gas pressure. It cannot be calibrated by simple calculation, and calibration must be done. The relative vacuum gauge is generally composed of a vacuum gauge tube as a sensor and a measuring device used for controlling and indicating. The reading is related to the gas type. There are many kinds of relative vacuum gauges, such as heat conduction vacuum gauge and ionization vacuum gauge.

    2. Classification according to the measuring principle of vacuum gauge

    According to the principle of vacuum gauge measurement, it can be divided into direct measuring vacuum gauge and indirect measuring vacuum gauge. The direct measurement of vacuum gauge is a direct measurement of the force on the unit area.

    (1) Static liquid level vacuum gauge. The pressure is measured by the liquid surface difference between the two ends of the U tube.

    (2) Elastic element vacuum gauge. The pressure value is measured by elastic deformation on the surface of the container connected to the vacuum.

    When the pressure is 10-1 Pa, the force acting on the surface of the 1cm2 is only 10-5 N. It is obvious that it is difficult to measure such a small force, but the change of pressure can be measured indirectly according to the change of the physical quantity related to the pressure of the gas under the low pressure. There are some indirect measurement gauges as below:

    (1) Compressed vacuum gauge. The principle is to apply Boyle's law on the basis of the U tube, which is to increase the pressure by isothermal compression, so that the pressure is measured by a U tube vacuum gauge, and then the measured pressure is calculated with the relationship between volume and pressure.

    (2) Heat conduction vacuum gauge. The principle of gas heat conduction under low pressure is related to pressure. The common used resistance vacuum gauge and the thermocouple vacuum gauge.

    (3) Thermal radiation vacuum gauge. The principle of thermal radiation of gas under pressure is related to pressure.

    (4) Ionizing vacuum gauge. The principle of the plasma flow changes with pressure is obtained by the collision and ionization of gas molecules with charged particles under low pressure. Such as hot cathode ionization gauge, cold cathode ionization gauge and radioactive ionization vacuum gauge.

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

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

    (7) Pressure vacuum gauge. Mixed gas partial pressure measurement is carried out by mass spectrometry. And the commonly used pressure vacuum gauge such as quadrupole mass spectrometer, cyclotron mass spectrometer and radio frequency mass spectrometer.