Volume Determination Leak Test Method
The volume determination, also called dosing method, is mostly used for so-called "closed components". These are completely sealed components that cannot be exposed to test gas via an opening. For example: watches, mobile phones, control units, etc.
The pressure change measurement takes place in a measuring chamber (bell) located around the test item.
This measuring chamber is not directly pressurized with overpressure or underpressure, but is filled via a pre-filling volume. This makes it possible to detect large leakages or missing components and to prevent incorrect measurements.
Any leakage in the test item leads to a pressure change within this chamber, which is recorded and evaluated by means of a pressure transducer or pressure difference sensor.
The principle of the dosing method can also be integrated into other measuring methods in order to carry out a volume determination, component presence detection or an exact gas quantity determination.
The following standard measuring procedures with the dosing principle are available:
- Volume determination C
- Volume determination with pressure change method DA
- Volume determination with pressure difference method DR
Test medium:
Compressed air/vacuum or nitrogen
Detectable leak rates:
Volume and pressure dependent > 1 cm3 / min
Detectable volume differences:
2-3% of the measuring volume, depending on the internal volume of the component
Method:
A known pre-fill volume is pressurized/vacuumed and stabilized. This gas volume is then fed into the test specimen or into the test specimen chamber. The resulting pressure is a measure of the volume and is used to detect coarse leaks. The additional pressure change caused by leakage is measured and evaluated.
Advantages:
- Simple and inexpensive method
- Volume determination, testing of closed parts possible if they have a free internal volume which is not less than approx. 10% of the free chamber volume.
- Standard method for waterproof consumer goods
Disadvantages:
- Relatively long Test duration
- Pressure shocks are possible due to the procedure