Veeco MS40 Operation And Maintenance Manual page 130

5.4.3.5
Helium at 760 Torr ±5% pressure is applied to the leak. If the leak has its
own supply of helium, this step is omitted. (Note: the filament of the
mass spectrometer tube may be turned off before Sec. 5.4.3.6.)
5.4.3.6
When the atmospheric air present between the calibrated leak and the leak
detector has been evacuated, the pump valve is closed.
5.4.3.7
The inlet valve is opened promptly after Sec. 5.4.3.6. The pressure in the
leak detector is allowed to reach a steady value, showing no observable
change in 1 min.
5.4.3.8
Turn on filament of mass spectrometer tube if it is not on.
5.4.3.9
At this point it may be necessary to change the sensitivity setting. When
the output signal has reached a steady value, showing a change in 1 min
which is not greater than the drift (as corrected for the sensitivity setting),
the output reading in scale divisions is noted. If the leak detector has been
set at reduced sensitivity, the reading should be converted to the
equivalent scale divisions for full-sensitivity setting.
5.4.3.10
Immediately after the proceeding step, the stopwatch is started and
simultaneously the leak isolation valve is closed as rapidly as practical.
Alternatively, the recorder chart may be marked to indicate the beginning
of the timed period and the leak isolation valve then closed rapidly.
5.4.3.11
The output is observed continuously and the stopwatch is stopped when
the reading has decreased to 37% of the reading observed in Sec. 5.4.3.9.
The reading of the stopwatch is noted (T sec.). Alternatively, the recorder
chart is examined to determine the time T required for the specific
decrease in output. T is the response time (Sec. 3.9.2).
Note: Should response time be a function of sensitivity setting, T as
observed should be corrected to response time at full sensitivity setting, if
any other setting was used.
Vacuum Instrument Corp.
2099 Ninth Avenue
Ronkonkoma, NY 11779
631.737.0900
1109-186-00 Rev. C b-viii