Agilent Technologies 5975C TAD VL MSD Troubleshooting And Maintenance Manual page 221

Diffusion pump control
The power regulator ensures that the diffusion pump heater receives constant
power, even if there are fluctuations in the AC line voltage. It measures the
voltage across the heater and the current through it, multiplies them together,
and compares the result with a standard value. Any discrepancy is applied as
an error signal to adjust the power.
If the power distribution board senses a malfunction in the diffusion pump
power regulator, it shuts off power to the diffusion pump. See
Hi vac power cable
Diffusion pump heater cable
Fore-
line
Fan
gauge
Diffusion pump harness
Figure 51 Diffusion pump control
Turbo pump control
Your MSD is equipped with a turbo pump with an integrated controller.
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.
5975 Series MSD Troubleshooting and Maintenance Manual
Diffusion
pump
HI VAC Power
Heater
Sensors
MSD electronics module
Harness
CAL
valve
8
Electronics
Figure 51.
(AC board)
221