Integral Leak Test Methods

The integral leak test is the measurement of the total leak rate of the whole test object. It can be carried out with two methods:

1.) from the inside to the outside

2.) from the outside to the inside

This methods do not give information´s about the leak location.

Integral leak test "outside - in"

The test object is evacuated by the helium leak detector. The outside of the test object is covered by some envelope or bell jar which is filled with 100% helium. With a bell jar the 100% filling can be achieved by evacuating the bell jar prior to the helium filling. At an envelope, which cannot be evacuated because it is weak (for example some plastic foil) the 100 % filling can only be achieved by flushing helium in and measure at an outlet opening the helium concentration.

If a leak is present, helium will come in and will reach the spectrometer which then displays directly the leak rate. With this kind of measurement the responsetime is insignificant (contrary to the leak location techniques) Possible the leak rate signal will increase slowly. The operator has to wait until the leak rate meter shows a stable leak rate.

Integral leak test "inside - out"

The test object is filled with 100% helium and placed under a belljar. The bell jar becomes evacuated by the helium leak detector. If a leak is present, wherever it is located, helium pures out and will be detected an displayed by the leak detector. The response time is given by the rest volume of the bell jar divided by the pumping effective pumping speed on the bell jar.

Large test objects, which cannot be placed under a bell jar, can be enbveloped by a plastic foil. With a sniffer probe the increase of the helium concentration under the foil is measured. Prior to the test the snifferprobe must be calibrated to measure helium concentration. This test can have long waiting times. The foil should be metalized for avoiding helium loses due to permeation. A detailed description of this procedure, including sample calculations, is given on the seminar on Leak Detection and leak test methods (see under products)