How to select the ideal Leak Testing Method for your Application
Every application and production process has its own demands and requirements when it comes to leak detection. In different industries, different standards are set in terms of quality control and maximum leak rates. Therefore, it is crucial to select the best leak detection method for every single application.
Within the last years, significant advances were made in the electronic leak testing technology, using either air or a tracer gas.
New techniques, improved sensitivity and faster test cycles – all of these technical evolutions have increased the quality and reliability of the different leak testing methods.
The pros and cons of these methods and their suitability for different leak detection applications as well as professional advice on selection criteria will be presented in the following.
Leak detection technologies – an overview
Before providing a guideline on how to select the right leak testing method for your application, the different technologies dealt with in this article will be presented in a general overview:
- Air leak testing with Micro-Flow sensor at pressure conditions
This technology is based on an integrated micro sensor working with an accelerated flow. When air leaks from the unit or assembly under test, the emitted air is replenished via the Micro-Flow sensor to maintain a constant pressure (see Figure 1). The loss causes an electrical signal proportional to the volume, respectively to the mass flow. The Micro-Flow sensor thereby operates with a pressure reservoir, which is used to pressurize the unit under test (UUT) and has a sensitivity of 5·10-4 mbar l/s. Usually, only simple fixtures are necessary for this type of testing method.
Fig.1: Working principle of a sector field mass spectrometer
- Air leak testing with Mass Extraction (vacuum conditions)
A special form of the Micro-Flow sensor technology is the so-called Mass Extraction technique. The basic principle is similar to the Micro-Flow approach, but in order to achieve higher sensitivity, the test is performed under vacuum conditions. This method incorporates sensor designs that operate at continuum/slip flow condition (lower vacuum) and transitional/molecular flow regimes (higher vacuum). This technology can be used for the leak testing of closed containers such as packages or electronic enclosures. The unit under test is placed into a vacuum chamber with pressure conditions of 1 mbar or less. After the chamber is evacuated, the remaining flow between the chamber and the vacuum reservoir is used to determine the leak rate of the tested part (see Figure 2). With this method, a sensitivity of up to 6.7 · 10-7 mbar l/s can be reached.
- Helium leak detection
Due to their comparatively simple and robust design, sector field mass spectrometers are used for leak detection with tracer gas. Typically tuned to a detection mass of 4 u for helium, the gas molecules are ionized in an ion source through electron bombardment and then accelerated into a magnetic sector field using electronic voltage. Alternatively, also hydrogen with a mass of 2 u can be used for this leak testing method. The helium or hydrogen molecules are able to pass through a dedicated slit in order to reach the detector while all other present molecules are unable to pass through and are thus re-neutralized. The measured ion current is proportional to the gas partial pressure. The helium sensitivity in a vacuum environment is 5 · 10-12 mbar l/s.
Read more about this state of the art technology in the attached application report.
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