3.11 Bakeout
Description
Power
distribution box
Emergency Off
switch
S2
switch
S3
switch
CBl, CB2,
and
CB3
circuit breakers
Bakeout
and
Main
Power
indicators
EMERGENCY OFF
The bakeout option adds a setpoint to control vacuum system bakeout
heaters. Bakeout is required to boil off molecules of a gas that are
either in or on system components to obtain required system pressure.
The bakeout option includes a power distribution box with front panel
controls and indicators. The following table describes the controls and
indicators shown in Figure 3-5.
Allows you to quickly shut down the system in case of emergency.
This switch is for vacuum bypass
When you tum this switch on for rough pumping, its associated
indicator lights.
CB 1, CB2, and CB3 are used for
Bakeout, Pumping Electronics,
and
Main Power,
respectively.
The
Bakeout
indicator lights when bakeout is on. The
Main Power
indicator lights when main power is on
Vacuum
Rough
Bakeout
Pumping
Main Power
Bypass
Pumping
Electronics
□
S2
S3
CB3
CB2
CB1
Figure 3-5. Front Panel ofBakeout Power Distribution Box
Bakeout
During bakeout, provisions must be made to limit temperature (to
procedure
prevent damage to the system components), shut off heaters if pressure
becomes too high (to prevent the gas load from stalling the pumps),
and shut off the heaters after a preset time interval (to end the
bakeout). Temperature limiting is done by sizing heaters to the system
(watts in vs. heat loss) or by reversible temperature limit switches.
Pressure limiting and timing is performed by the DIGITEL.
3-18
Operation
