168 5977B Series MSD Troubleshooting and Maintenance Manual
6 Vacuum System
Foreline Gauge
The foreline gauge monitors the pressure (vacuum) at the exit of the diffusion
pump. The primary function of the foreline gauge is diffusion pump control.
When the foreline pump has reduced the pressure in the analyzer chamber to
below 300 mTorr (0.3 Torr), the diffusion pump is automatically switched on.
If the foreline pressure rises above 400 mTorr (0.4 Torr), the AC board
switches off the diffusion pump heater and the analyzer electronics.
Monitor the foreline pressure from the data system or the LCP.
The foreline gauge is used only with diffusion pump MSDs.
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