A test gas is applied in (high) vacuum technology inspection on a number of different test objects for detection of leaks. The tightness inspection is one of the destruction-free testing methods. Tightness inspections are used on a large scale in industrial manufacture and quality inspection.
Helium is used for vacuum devices as the most highly diffusible leakage detection gas through evacuation of the vacuum apparatus using a pump and hanging a mass spectrometer behind the pump. When the apparatus is now blasted with helium from the outside, only locally in order to detect leakages, a possible penetration of helium into the apparatus can be detected and the leakage rate measured using the mass spectrometer.
A leak is a hole in a product or technical system through which solids, liquids or gases can enter or escape undesirably. A leak can cause failure of the entire technical system. One parameter for measuring the extent of the leak is the leakage rate.
Leakage detection using a test gas is based on production of a pressure difference between the test object and the detection device. This can be achieved through increase or decrease of the pressure on one side of the test object in comparison with the other side or a combination of pressure reduction and pressure increase. In the case of a leak a constant gas current is produced from the high pressure side to the low pressure side. If there is a detection device for the gas current on the low pressure side the leakage can be proven qualitatively or quantitatively.
The test gas helium dominates the test gas methods, as it only exists in low natural concentration of ca. 5 ppm. As a noble gas, it does not enter any chemical reactions under normal conditions and for this reason is very safe. It can be detected with a high degree of selectivity and cross-sensitivity in the inspection.
A mass spectrometer set to the helium mass 4 which forms a compact leakage detection device that is easy to operate together with the corresponding gas distribution and vacuum system is used as a detection device.
The work pressure of the mass spectrometer is between < 10−4 mbar. In commercial leakage detection devices the mass spectrometer is also always combined with a vacuum system which consists of at least a mechanical booster pump, a high-vacuum pump, pressure measuring devices as well as a series of controlled pressure-dependent vents. An integrated test leak with which the leak detection device can be calibrated is also in compliance with the current technical standards.
Prior to leakage detection it must be ensured that the test object is clean and dry.
Degassing through vapors or liquid residue prolongs the pump and accordingly the inspection time.
The registered contamination curtails the service life of the measuring device.
This efficient and sensitive leak detection method is performed at our company by qualified experts.