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How to determine the sensitivity of the helium mass spectrometer leak detector of the coating equipment?

How to determine the sensitivity of the helium mass spectrometer leak detector of the coating equipment?

2020-09-05

How to determine the sensitivity of the helium mass spectrometer leak detector of the coating equipment?
PVD vacuum coating machineThe mass spectrometers used for residual gas analysis in vacuum coating equipment can all use H
, He, Ar, etc. as leak detection materials for leak detection, but the leak detection sensitivity of these leak detectors is different. Since the 1940s, the application of mass spectrometers in leak detection has further advanced the development of leak detection technology. The evaluation of a helium mass spectrometer leak detector requires a comprehensive understanding of its main performance indicators. Sensitivity is the main parameter of a helium mass spectrometer leak detector. As the sensitivity of a helium mass spectrometer leak detector is inconsistent in various countries in the world, in my country, Basically, the minimum detectable leak rate is used to express the sensitivity of a helium mass spectrometer leak detector.

The minimum detectable leak rate (sensitivity) of the helium mass spectrometer leak detector refers to the “dynamic detection” when the leak detector is in an optimal working condition (the leaking gas is pure helium at an atmospheric pressure). The leak rate of the smallest leak that can be detected when “leak”.

1. The best working conditions.

It means that the material of the tested coating equipment components has little out
-gassing and no large leaks; the parameters of the leak detection device itself are adjusted to the best working condition, etc.

2. Dynamic leak detection.

It means that the leak detection is not performed by the accumulation method, the vacuum pumping system of the leak detection device itself is still vacuuming normally, the reaction time of the device is less than 3s, and the time constant of the pumping system in 3s is less than one second;

3. The smallest checkable.

Means that its signal is twice the noise floor;

4. Leakage rate of leaks.

Refers to the leakage rate of dry air (pressure of 100kPa) to the vacuum end (pressure far below 100kPa) through the leak.

For a helium mass spectrometer leak detector that responds to changes in helium partial pressure, in order to characterize this reaction characteristic, it is best to give the minimum detectable concentration of the leak detector, that is, concentration sensitivity. The so-called "concentration sensitivity" of the leak detection device refers to the change in the minimum helium concentration in the atmosphere that can be detected by the mass spectrometer chamber under working pressure (the working pressure is generally 10⁻²Pa~10⁻³Pa). The "minimum detectable concentration" in the helium mass spectrometer leak detector of the coating equipment is the helium concentration when the signal to device noise ratio is one or two.


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