Veeco MS40 Operation And Maintenance Manual page 40

Sniff Testing:
Sniff Testing is performed by checking for escaping helium in a test
object already filled with helium gas. Sniff testing is unique in that:
By passing the sniffer probe over a suspected leak, out flowing helium
from the test object is drawn into and measured by the system. This type
of testing is most useful when testing large objects (e.g., large tanks) or
when testing items that cannot withstand internal vacuum. Note that this
type of testing is the least sensitive that the MS-40 can perform. A sniffer
probe ultimately draws in some surrounding air that acts to dilute the helium
leak tracer. Also note that sniffing is primarily a qualitative form of
testing rather than a quantitative test; it is best used for locating leaks
rather than measuring them.
The procedure for Sniff Testing is as follows:
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1 Leak detection is performed through a small orifice (a sniffer
probe) that is attached to tubing that is then connected to the
leak detector, and
2 the test object itself is not evacuated during testing.
1 Remove the plug that covers the sniffer port. Install the sniffer
probe.
2 On the Service Panel press the SNIFF momentary switch. The
Sniffer indicator light should now be lit.
3 The automatic ranging mode indicator is also lit. If the manual
ranging mode is needed, press the Automatic/Manual Ranging
button and set the expected leak rate range with the arrow keys.
In either case, the unit will be able to test leaks within the 10
-8
10 std cc/sec range.
4 Press the START pushbutton. The filament will be
momentarily
turned off while the sniffer is evacuated and the MS-40 crosses
over into sniffing mode.
5 When the green Start light is illuminated, the unit is ready for
testing. Using the probe, examine the test object for leaks.
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