Functional Description Of Operation - Veeco MS40 Operation And Maintenance Manual

3.3
The MS-40 is a portable, helium mass spectrometer leak detector that may be
used for both quantifying and locating leaks in objects that can be evacuated or
pressurized. Helium that is present in a test object is drawn into the unit
(either through the test port or through the sniffer valve), isolated and detected
by a mass spectrometer, and converted into an electric signal. The electric
signal generated is proportional to the leak rate of the helium drawn through
the leak found in the test object. Once this signal is amplified, the signal is
displayed as a leak rate on the User Panel of the MS-40.
Helium is used as a tracer gas because of its unique combination of properties:
The operation of the MS-40 is discussed below. The operator of the unit
should use this information in conjunction with the unit's Vacuum
Schematic (as illustrated in Figure 3-1). The description follows the
sequence of a basic test cycle. A test cycle is started by connecting a test
object to the test port (or by connecting the sniffer probe to the sniffer
port) and by pressing the START button.
Prior to testing, ensure that the unit is in its functional READY state. The
START-UP procedure is described in Section 2.3. When the unit is ready
for testing, the vacuum system will have the following status:
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Functional Description of Operation

• Helium is present in the atmosphere at a rate of only 5 parts per
million (ppm), therefore it is unusual to find a high atmospheric
background of helium that may disrupt testing
• Helium is neither explosive nor toxic; it is completely inert and
will not contaminate a test object
• Helium does not contaminate or desensitize its own detector as
is common with detectors using other tracer gases
• Helium molecules are small (mass 3 or 4 helium may be used
for the MS-40) and therefore flow readily through extremely
small leaks.
1 The internal mechanical pump and the turbo-molecular pump
will be functioning; the external mechanical pump will also be
functioning (if installed).
2 The fore-line valve will be open; all other valves will be closed.
3 The "Hi-Vac" system will be fully evacuated by the turbo-
molecular pump.
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