Ac Board - HP 5973 Hardware Manual

AC board

The ac board is mounted on the opposite side of the electronics panel from the
HP-IB/MS control card. The ac board is also sometimes called the power distribu-
tion / vacuum control board. The ac board performs the following functions:
• Has two sockets for connecting the toroid transformer. The socket used
depends on the line voltage.
• Distributes ac line power to the ac/dc power supply, the foreline pump, the
toroid transformer.
• Turns on the diffusion pump once the foreline pressure is low enough.
• Regulates the ac power to the diffusion pump heater.
• Turns off the diffusion pump if the foreline pressure is too high or if the diffusion
pump is too hot.
• Controls the foreline gauge.
• 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.
• Provides power and logic interface to turbo controller.
• Turns the calibration valve on or off as directed to by the main board.
• Turns the diffusion pump on or off as directed to by the main board.
• Provides the voltage for the calibration valve.
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 com-
pares the result with a standard value. Any discrepancy is applied as an error sig-
nal 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.
In turbo pump MSDs, the ac board sends control signals to, and receives turbo
pump status information from, the turbo pump controller.
Electronics
8

AC board

241