The original vacuum gauge was invented by Torricelli, a slender glass tube filled with mercury at one end. According to the measuring range of vacuum degree and using environment, the most commonly used vacuum gauges are capacitive diaphragm vacuum gauge, thermocouple vacuum gauge, hot cathode ionization vacuum gauge and cold cathode ionization vacuum gauge.

These kinds of vacuum gauges make use of different physical phenomena. The capacitive diaphragm vacuum gauge uses force, the thermocouple vacuum gauge uses heat conduction, and the ionization vacuum gauge uses vacuum discharge.

The following points should be paid attention to when selecting vacuum time meter:

1： Whether the vacuum gauge has enough measurement accuracy within the pressure range required by the equipment;

2： Whether the measured gas will damage the vacuum gauge;

3： Whether the vacuum gauge will affect the measured vacuum environment;

4： Whether the pressure measured by the vacuum gauge is full pressure or partial pressure, whether it has been calibrated, and whether it is related to the type of gas;

5： Whether the vacuum gauge can realize continuous measurement, numerical indication and reaction time;

6： The stability, reliability and life of vacuum gauge.