218 5977B Series MSD Troubleshooting and Maintenance Manual
8 Electronics
The AC board sends control signals to, and receives turbo pump status
information from, the turbo pump controller. The turbo pump controller
provides power to the turbo pump and regulates pump speed. If the pump fails
to reach 80% speed within 7 minutes after beginning pumpdown or if the
speed drops below 50% during operation, the controller shuts off the turbo
pump and the AC board shuts off the foreline pump.
Pumpdown failure shutdown
The AC board will shut down both the high vacuum and the foreline pump if
the system fails to pump down correctly. Other conditions that trigger
shutdown are turbo pump speed below 80% after 7 minutes, or foreline
pressure above 300 mTorr after 7 minutes.
This is usually because of a
large air leak: either the sideplate has not sealed
correctly, or the vent valve is still open. This feature helps prevent the foreline
pump from sucking air through the system, which can damage the analyzer
and pump.
To correct the problem, power cycle the MSD and troubleshoot. You have
7 minutes to find and correct the air leak before the system shuts down again.
Press on the side plate when turning on the MSD power to ensure a good seal.
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