helium mass spectrometer leak detector classification and structure principle
Nitrogen mass spectrometer leak detector is a kind of leak detection instrument which uses helium as leak detection gas. It has the characteristics of stable performance and high sensitivity. It is the most sensitive and widely used leak detection instrument in vacuum leak detection technology.
Helium mass spectrometer leak detector is a mass spectrometer with magnetic bias transformation. The sensitivity of the single-stage magnetic deflection transformation instrument is 10-9 ~ 10-12 pam3 / s, which is widely used for leak detection of various vacuum systems and components. Compared with the single-stage magnetic deflection transformation instrument, the background noise of the two-stage series magnetic deflection transformation instrument is significantly reduced. Its sensitivity can reach 10-14-10-15 pam3 / s. It is suitable for leak detection of ultra-high vacuum system, parts and components. The counter current helium mass spectrometer leak detector has changed the structure and layout of the conventional instrument. The tested piece is placed in the front stage of the main pump of the leak detector. Therefore, it has the characteristics of leak detection under high pressure, no need of liquid nitrogen and less pollution in the mass spectrometer room. It is suitable for leak detection of vacuum system with large leakage rate and poor vacuum sanitation, and its sensitivity can reach 10-12 pam3 / s.
The helium mass spectrometer leak detector is composed of ion source, analyzer, collector, cold cathode ionization gauge, gas extraction system and electrical part.
Single stage helium mass spectrometer leak detector
In the mass spectrometer room, there are: ion source composed of filament, ionization chamber and ion accelerator; analyzer composed of external uniform magnetic field, baffle and outlet gap; collector composed of suppression grid, collector and high resistance; first stage amplification electrometer tube and cold cathode ionization gauge.
In ionization chamber n, the gas is ionized into positive ions, and the ions are focused into beams under the action of electric field. Under the action of accelerating voltage, the analyzer enters the analyzer through the gap of accelerating pole S1 at a certain speed. Under the action of a uniform magnetic field, the ions with a certain velocity will move in a circular trajectory, and the deflection radius can be calculated according to the formula.
It can be seen that the deflection radius r of the ion beam with different mass charge ratio Me-1 is different when B and u are constant. The B and R of the instrument are fixed, and the accelerating voltage U is adjusted to make the helium ion beam [in the figure (Me-1) 2] pass through the outlet gap S2 and reach the collector D, forming an ion current which is amplified by the amplifier. The ion beam, which is different from helium mass charge ratio [(Me-1) 1 (Me-1) 3], cannot pass through the exit gap S2 due to its different deflection radius and R value of the instrument. (Me-1) 2 = 4, i.e. the mass charge ratio of He +, except he +, C 30 is very small and can be ignored.
Double stage series magnetic bias transition helium mass spectrometer leak detector
The mass spectrometer of the double-stage 900 reduced series magnetic bias helium mass spectrometer leak detector. Due to the two analyses, the probability of non helium ions reaching the collector is reduced. Moreover, if an accelerating electric field is set between the two analyzers, that is, the gap S2 in the figure and the adjacent baffle plate, the ions will be accelerated again before entering the second analyzer. Although the non helium ions with the same momentum as helium ions can pass through the first analyzer, they are separated due to their different momentum from helium ions after entering the second analyzer after the second acceleration. Due to the secondary separation, the background and background noise of the instrument are significantly reduced and the sensitivity of the instrument is improved.
Countercurrent helium mass spectrometer leak detector
The structure features of countercurrent helium mass spectrometer leak detector. This kind of instrument is made according to the principle that the compression ratio of oil diffusion pump or molecular pump is related to the type of gas. For example, the compression ratio of multi-stage oil diffusion pump for helium is 102, and the compression ratio for other components in air is lo4-106. During leak detection, some of the helium entering the front stage of the main pump through the leak hole on the inspected part still flows back to the mass spectrometer room, and the leakage signal is displayed by the output indication of the instrument.