Electronics 8
5977B Series MSD Troubleshooting and Maintenance Manual 217
• Turns off the diffusion pump if the foreline pressure is too high or if the
diffusion pump is too hot.
• Passes the foreline pressure signal from the foreline gauge or turbo pump
speed and other vacuum status information to the main board.
• Turns off the foreline pump in case of a problem with pumpdown.
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 Figure 52.
Turbo pump control
Your MSD is equipped with a turbo pump with an integrated controller.
Figure 52 Diffusion pump control
Hi vac power cable
Diffusion pump
harness
Diffusion pump
heater cable
Fan
Diffusion
pump
Heater
Sensors
HI VAC Power
Harness
CAL
valve
MSD electronics module
(AC board)
Fore-
line
gauge
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