Veeco MS40 Operation And Maintenance Manual page 46

system valves. Also displayed in the schematic are the user-adjustable
time delays of the rough, fine and vent valves and how they impact the
test cycle.
The ways in which delay settings may be used to benefit certain testing
conditions are described below:
D1/Fine Crossover Delay: Occurs after Crossover 2 has been reached
and refers to the delay (in seconds) between the attainment of Crossover 2
and the onset of Direct testing (the opening of the Fine valve).
With D1 at the factory default setting, the Fine valve will open 1.0
second after the Crossover 2 set point has been reached. The MS-40
remains in Reverse flow testing for the duration of D1.
-10
Note that if the MS-40 is set for Manual ranging on the 10 range, the
unit will remain in the roughing state after reaching Crossover 2 for the
duration of D1.
The ability to delay the actual crossover is useful for testing objects
greater than one liter or when the test object has a high out gassing rate.
The additional roughing of the test object prior to opening the Fine valve
reduces the possibility of a crossover (pressure) burst and limits the
chance of burning out the mass spectrometer filament prematurely.
D2/Direct Rough Valve Close Delay: Occurs when Crossover 2 has been
reached; represents the amount of time (in seconds) that the Rough valve
remains open after the Fine valve opens (the Rough valve needs to be
closed so that Fine Testing may occur). With D2 at the factory default
setting, the Rough valve closes 0.1 second after the Fine (Direct) valve
opens (i.e., after Crossover 2 set point has been reached). D2 may be set
from 0.1 to 999.9 seconds.
If the test object has a large volume, or the test material produces a larger
than normal amount of out gassing, it will probably be helpful to increase
this delay limit in order to limit the pressure burst that occurs during
crossover.
D3/Vent Delay: The Vent Delay is the period of time (in seconds) that
the MS-40 operator must hold down the "VENT" pushbutton before
venting of the test object will occur. The delay is useful to prevent
accidental venting of the system. The factory default for D3 is 1.0
second. This time is usually sufficient to prevent accidental
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activation of the vent cycle. The vent delay may be programmed from 0.1
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to 999.9 seconds.
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