HP 5973 - Page 33

2 Operating the MSD
33
The data system helps you pump down the MSD
Pumpdown is mostly automated. Once you close the vent valve and turn on
the main power switch (pressing on the sideplate), the MSD pumps down
by itself. The data system software contains a program that monitors and
displays system status during pumpdown. When the pressure is low enough,
the program turns on the ion source and mass filter heaters. It also prompts
you to turn on the GC/MSD interface heater. Newer MSDs will shutdown if
they cannot pump down correctly.
Pressure in the MSD can be monitored two ways
The diffusion pump MSD is equipped with a gauge that measures foreline
pressure. Foreline pressure can be monitored only through the data system.
The turbo pump MSD does not have a foreline gauge. Instead, the data
system displays turbo pump motor speed.
Each MSD is equipped with a triode gauge tube. If your MSD is also equipped
with an HP 59864B Gauge Controller, the triode gauge can measure the
pressure in the vacuum manifold. The high vacuum pressure measured by
the triode gauge cannot be monitored through the data system. It is dis-
played on the gauge controller.
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