7.2.4 Calibrating the leak detector
The leak detector must be calibrated in order to determine leakage rates. This is done using a commercial test leak, which generates a known and reproducible test gas rate under defined conditions. Commercial test leaks are available in the form of a permeation leak or a capillary leak with or without a test gas reservoir. Leak detectors are usually equipped with permeation leaks with a helium reservoir. For calibration, an appropriate working cycle is often built in that automatically performs the calibration.
To obtain precise measurements, the unit should be calibrated before each use. To test large test specimens for which additional vacuum pumps are in use, it is advantageous to use an external test leak. The measurement accuracy can depend on where the test leak is attached. Consequently, it is necessary to take flow conditions within the vacuum area into consideration. The use of external test leaks is also useful for deter-mining the maximum response time.