Veeco MS40 Operation And Maintenance Manual page 62

all valves except the fore-line will be closed, the turbo pump will be turned
off, and ERROR 01 will be posted. See Error Codes in section 4.10 for further
information. The crossover pressure (Crossover 1) should be adjusted by
the User to provide the shortest possible test cycle duration without producing
excessive pressure bursts into the fore-line region of the unit. Note that
since fore-line tolerance is very high, the usual result of the increase of
fore-line pressure will be a variable background reading.
If no measurable leaks are found in Reverse Flow mode, Direct Flow
testing begins. Within the vacuum system, the fine valve is opened
while the rough valve closes. At this point the test port is fully connected
to the high-vacuum section. The equalization of the two pressures will
cause a pressure burst in the high-vacuum section. If the burst is over
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5 x 10 Torr, the mass spectrometer filament will be turned off for 10
seconds and ERROR 02 will be posted. The system will then turn the
filament back on and attempt to resume testing (see Error Codes, section
4.10, for further information).
To prevent an excessive pressure burst, the test port may be evacuated for
a longer period by lowering the crossover pressure (Crossover 2 - refer
to Section 2.7 for information on how to adjust this parameter) or by
changing the "delay" setting (refer to Section 2.7 for detailed information
on delay parameters). In this case, delay refers to either delaying the
opening of the fine valve (the direct gateway between the high-vacuum
section and the test port) or the closing of the rough valve (allowing
further evacuation of the test port/test object area). Optimizing these two
parameters allows the user to shorten the test cycle while still being able
to safely operate the unit.
Often the setting of delays will depend on the size of the test object. Smaller,
cleaner objects will tend to produce small pressure bursts and therefore use
relatively high crossover set points. Larger, dirtier objects tend to produce
larger bursts that can be prevented by extending the roughing time to delay the
onset of Direct Flow mode testing.
After Crossover 2 has been reached, and the unit is in the Direct testing mode,
pressure in the test object continues to be reduced until it is equalized with the
high-vacuum section. Concurrently, the MS-40 ranges downward to the
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ultimate Direct Flow sensitivity of 4 x 10 std cc/sec, unless a larger leak is
found.
At the end of the test the test is terminated by pressing either the VENT
or START pushbuttons. The unit's computer will then close either the
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fine, rough or gross valve (dependent on the current testing mode). Note
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