Measurement of vacuum degree

The vacuum gauges used in vacuum pumps can be divided into two categories:

One is the absolute vacuum gauge that can directly measure the system pressure, such as the Mcleod vacuum gauge.

The other kind is the relative vacuum gauge used after the absolute vacuum gauge calibration, the thermocouple vacuum gauge and the ionization vacuum gauge are the most commonly used relative vacuum gauge. Those that from its measured quantities (such as the liquid column height, working liquid, proportion, etc.) directly to calculate the gas pressure that the absolute vacuum gauge, the vacuum gauge measuring accuracy is higher, mainly used as a benchmark for measuring tool. Relative vacuum gauge is mainly use some physical characteristics of gas under low pressure, such as heat conduction, ionization, viscosity and strain, etc.) and stress the relationship between the indirect measurement, the measurement accuracy is low, and the measurement result is related to the measured gas type and composition.

Therefore, the relative vacuum gauge must be calibrated and calibrated with an absolute vacuum gauge. But it can read the pressure directly, easy to use, in the practical application of the overwhelming majority. Vacuum technology need to measure pressure in the range of 105 ~ 10-11 pa, even smaller, 16 orders of magnitude more wide, no vacuum gauge can apply to one from the rough vacuum, low vacuum and high vacuum, the ultra high vacuum to high vacuum full range of measurement, so need to have a variety of combination of vacuum gauge to measure.

The most commonly used vacuum gauges are as follows:

(1) u-tube vacuum gauge. The u-tube vacuum gauge is used to measure the absolute vacuum of the coarse and low vacuum. The u-shaped glass tube is filled with working fluid (low vapor pressure oil, mercury). One end of the tube is pumped into a vacuum (or directly through the atmosphere), and the other end is connected to the vacuum system.

(2) compression vacuum gauge. The compressed vacuum gauge, also known as the McLean vacuum gauge or the MCS vacuum gauge, is an absolute vacuum gauge that measures low vacuum and high vacuum. This kind of vacuum gauge is made of hard glass.

(3) resistance vacuum gauge. The resistance vacuum gauge, also known as the pirani vacuum gauge, is a relative vacuum gauge which measures the low vacuum. It is composed of two parts: the resistive regulator and the measuring circuit.

(4) hot cathode ionization vacuum gauge. The thermal cathode ionization vacuum gauge is mainly used for high vacuum measurement. It is composed of a cylinder-type hot-cathode ionization gauge and a measuring circuit.

(5) cold cathode ionization gauge. A cold cathode ionization gauge is a relative vacuum gauge that measures high vacuum. It consists of two parts: ionization gauge and measuring circuit.

(6) thermocouple vacuum gauge (also known as thermocouple gauge). Composed of heating wire and thermocouple, the top is connected to the vacuum system.