3.4
Autorun
Pump
temperature
Cool-down
mode
Power failure
AUTORUN continuously monitors voltage and current and calculates
the power applied to the pump in order to control ion pump operation.
AUTORUN determines the size of the pump from the position of the
rear panel pump size switches and can then determine how much heat
the pump can dissipate. This information (power in, power out) is
used to calculate the temperature of the pump elements.
Pump temperature is important because:
• ion pumps can be damaged by excessive element heating
• as the temperature of the elements increases, the rate of outgassing
increases, and causes thermal runaway if this rate is high enough
When pump temperature becomes too high, AUTO RUN forces the
DIGITEL into cool-down mode. It turns power off and lets the
elements cool to reduce the outgassing to an acceptable level, then
turns the pump back on.
AUTO RUN also forces the DIGITEL into cool-down if it detects
thermal runaway. If the voltage is between 1000 and 3000V and drops
rapidly (as would happen if the pump went into thermal runaway while
starting), the DIGITEL immediately enters the cool-down mode
regardless of calculated element temperature.
While in the cool-down mode, the message
COOL
is displayed, and
high voltage is off. After five minutes, high voltage automatically
turns back on and the DIGITEL starts the pump again. If the DIGlTEL
cannot get the pump operating after four cool-down cycles, it shuts the
pump off and displays
Err 5.
This indicates that a problem exists and
care must be taken when operating the pump.
The run/cool cycle limit count is reset to zero whenever power is
turned on, the
OPER
button is pressed, or after the pump has operated
at 5 x 10-
6
torr or less. The cool-down cycle may be aborted, and high
voltage reapplied by pressing the
OPER
key.
AUTORUN restarts the pump after power failure if the
HV ENABLE
switch is on.
Operation
3-7
