The influence of gas type on vacuum measurement

    (1) The influence of gas type on measurement readings.

    For direct measurement vacuum gauges such as elastic element vacuum gauges and capacitive thin film vacuum gauges, the measurement result is the total pressure of gas and steam, and has nothing to do with the type of gas. For indirect measurement vacuum gauges such as heat conduction vacuum gauges and ionization vacuum gauges, the measurement results are related to the gas type and composition, so the readings need to be considered for correction.

    If the measured gas is nitrogen, inert gas or relatively pure air, it is relatively simple, because ordinary vacuum gauges are calibrated on this basis before leaving the factory, and the actual measured reading is its true pressure value. But in many cases, the measured gas is often a different combination of air, special process outgassing, water vapor, oil vapor and other gases and vapors, which will affect the measurement results of the relative vacuum gauge. Therefore, the concept of relative sensitivity is usually introduced and corrected for different gases.

    (2) The influence of gas type on vacuum gauge.

    Various vapors in the measured gas will also affect the vacuum gauge. Among them, oxygen, water vapor, oil vapor and other components have a serious impact on the vacuum gauge. When measuring with a resistance vacuum gauge, oxygen and water vapor will oxidize the hot wire of the gauge and change the surface state of the hot wire; oil vapor attached to the hot wire and the wall of the gauge will change the surface properties, and therefore will cause regulation. The zero drift and sensitivity changes cause inaccurate readings. When measuring with a high-pressure hot cathode ionization vacuum gauge, oxygen and water vapor will obviously deplete the hot cathode of the gauge; the hydrocarbons generated by the decomposition of oil vapor on the surface of the high temperature cathode or electron bombardment will contaminate the electrode and the wall of the gauge. Significant changes have taken place in regulatory sensitivity and characteristics. Therefore, in the rough and low vacuum area, to measure the pressure of oxygen, water vapor or oil vapor, a capacitive thin-film vacuum gauge is usually used.

(Huiputech)