Helium mass spectrometer leak detector method of suction nozzle

 

Used for vacuum residual gas analysis mass spectrometer can be used to leak detection (its material leakage of hydrogen, helium, argon, etc.), but different leak detection sensitivity. Is dedicated to the leak detection of mass spectrometer is called mass spectrometer leak detector. Its characteristic is high sensitivity, stable performance. Especially made in helium leak gas helium mass spectrometer leak detector, is highest in the vacuum leak detection sensitivity, use one of the most common leak detection instrument.

 

Figure 5.6 method of suction nozzle leak detection

Helium mass spectrometer leak detector sensitivity, the minimum leakage rate, is under the condition of the instrument is in the best work, 1% of the helium at 0.1 MPa and 99% of nitrogen in gas leakage, during dynamic leak detection can detect the minimum leakage hole leakage rate. What is known as "the best working conditions" refers to checked a little gas, and no large hole leakage, and adjust the parameters of the instrument itself is to the best working state and other conditions; The so-called "dynamic leak detection" namely leak detection without accumulation method, the leak detector itself of vacuum system is still in the normal extraction, the response time of the instrument is not more than 3 s (including vacuum system time constant is not greater than 1 s), and so on and so forth. "Minimum inspection" refers to the signal is twice the background noise; "Leakage rate" refers to 0.1 MPa dry air to the vacuum side through hole leakage (pressure is far less than 0.1 MPa) leakage rate. The sensitivity of helium mass spectrometer leak detector method of suction nozzle is about 10 to 9 cubic cm/s.

 

The response time The response time of this method is about 2 ~ 3 s, it mainly includes two aspects: one is the response time of the leak detector itself; Another is the leakage of helium is sucked into the leak detector response time.

Each manufacturer production of the helium mass spectrometer leak detector itself in the same response time. Detection part of vacuum in vacuum pump exhaust velocity had a great influence on the response time. Helium gas exhaust velocity is smaller, the easier it will be easy to savings in checked, so as to shorten the response time. Helium gas flow from the leak point to the inlet hole need a certain amount of time, usually about 1 s.

Leak of judgment Using this kind of leak detector, suction nozzle (probe) with 2 ~ 5 m/min slow speed along on the surface of the detected movement. If there is leakage, you can see the gauge pointer swing, can also hear the sound of the oscillator is changed, thus can judge the leakage point or near the leakage. When testing can make the suction nozzle from the place where suspicious, signal back to the original state. Wait for a moment after (usually 2 ~ 5 s), then the suction nozzle is suspicious. Repeat the above operation a few times, can accurately judge the leakage points, precision can reach about 1 mm.