Advantages of helium mass spectrometry vacuum leak detection method

Helium    High purity helium

Helium mass spectrometer leak detection involves blowing helium gas from the outside of a vacuum chamber onto the area being tested, and then detecting the ingressed helium gas using a helium mass spectrometer leak detector connected to the vacuum chamber. This is currently the most commonly used method for vacuum leak detection. For purchasing high-purity helium gas, please contact Wuhan Yisituopu Technology Co., Ltd. Click for online inquiry or call our hotline: +86 189 8614 9031.

The basic principle of a helium mass spectrometer leak detector is illustrated in Figure 1. Thermoelectrons emitted by the filament accelerate towards the anode and ionize gas molecules upon encountering them. A magnetic field is set up on the way towards the ion collector, causing the ions to move in a circular trajectory due to Lorentz force. Assuming the mass of the ion is m and its charge is e, the radius of the circular trajectory is related to the mass-to-charge ratio m/e. By reasonably setting the position of the exit slit, m/e can be made equal to 4, allowing He+ to pass through the slit. Other ions with different mass-to-charge ratios from helium cannot pass through the exit slit due to their deflection radius differing from the slit setting of the instrument. Therefore, the helium mass spectrometer leak detector can only detect monovalent helium ions. When using a helium mass spectrometer leak detector, it is usually required that the vacuum degree of the detected space be below 10-3 Pa, with a detection accuracy up to 10-13 Pa·m3·s-1.

Helium mass spectrometer leak detectors are characterized by stable performance and high sensitivity. Sensitivity, response time, zeroing time, working vacuum degree, ultimate vacuum degree, and pumping speed at the instrument inlet are the main performance indicators for evaluating helium mass spectrometer leak detectors.

The main reasons for using helium as a test gas are as follows:

(1) It is non-toxic to human body and natural environment;

(2) It cannot burn, ensuring operational safety;

(3) Inert gas, which does not chemically react with the object being tested;

(4) With small molecular diameter and mass, it is easy to pass through tiny gaps, facilitating leak detection;

(5) Under normal conditions, it remains in a gaseous state and will not block micro-leakage holes;

(6) The gas emitted from the vacuum chamber itself almost does not contain helium;

(7) Helium only exists in the air at a concentration of 5ppm, making it easy to pinpoint the location of any leaks.

Since helium is much lighter than air, when spraying helium into a vacuum chamber for leak detection, it is necessary to operate from top to bottom, otherwise it will be difficult to determine the location of the leak. When the chamber structure is complex or the leak rate is extremely low, it is possible to cover key areas with plastic bags and then fill the inside of the plastic bags with helium to achieve leak detection of specific key areas.

Generally, the following parts should be paid special attention to during vacuum leak detection:

(1) Flange interface part;

(2) Welding position;

(3) Bellows part;

(4) Other sealing parts.