Leak Testing - Veeco MS40 Operation And Maintenance Manual

2.4

Leak Testing

Leak testing is most often performed on the MS-40 by connecting a test
object to the leak detector test port. The unit's leak detector test port is
located on the top right of the MS-40 s housing.
Vacuum Testing:
Through the use of the detector's internal rough pump (and external rough
pump, if so equipped) the test object is evacuated. Once accomplished,
the area of the test object suspected to have a leak is sprayed with helium
gas. If there is a leak, the helium (and other gases) will pass through the leak
in the test object:
1 The gases entering the unit are ionized (positively charged).
2 Helium molecules are separated from all other gas molecules.
3 Helium ions will then strike the collector plate causing an
electron flow equivalent to a minute current, which and
amplified so that the measurement of the leak is displayed
on the User/Service Panel.
An alternate, commonly used method is to test an object pre-filled with
helium gas. The test object is placed in a test chamber that is evacuated
and tested (as above). The MS-40 subsequently displays the measurement
of the leak on the User/Service Panel.
The procedure for leak testing an object in the MS-40 (without an external
pump connected) is as follows :
1 Connect the test object to the test port located at the top of the
MS-40.
2 Press the green START pushbutton.
3 The reverse/fore-line valve closes, the rough valve opens and
the test object is evacuated.
4 When the test port pressure reaches Crossover 1 (7.5 Torr
maximum), the reverse/fore-line valve opens.
1109-186-00 Rev. C 2-20