Brooks On-Board 8, Инструкция по установке и обслуживанию

Страница: 38 / 56

4-2 ©2013 Brooks Automation Inc. Pub. No. 8040564, Rev. AA, 01/15/13 ECO No. 64541
NOTE: If the On-Board GLE Cryopump does not reach its normal
operating temperature (below 20K), then that performance degradation
may be caused by any of the following:
a. Helium gas contamination
b. Poor vacuum
c. Thermal load on the On-Board GLE Cryopump arrays
Performing a Fast or Full regeneration cycle will not remove gaseous
contamination from an On-Board helium circuit. Unless the
decontamination procedure is performed, the noisy On-Board GLE
Cryopump condition will repeat itself within one - four weeks.
Background
The On-Board GLE Cryopump contains a cryogenic refrigerator assembly
called a
coldhead . There is no way to visually inspect the internal
components, so it is best to detect problems by listening for unusual
sounds. If the coldhead runs quietly at start up, but begins to make a
ratcheting noise after the On-Board GLE Cryopump is cooled down, then
contaminated helium is the most probable cause.
All gases other than helium can freeze in the coldhead. During
manufacturing of On-Board GLE Cryopump systems, gaseous impurities
are removed using stringent manufacturing control. The delivered system
contains sufficiently low concentrations of gaseous impurities so they are
not of concern.
It is possible, over long periods of operation, that additional gaseous
contaminants can be released. These gases, along with any air that is added
accidentally during installation, will collect in the coldhead as frozen gas.
The frozen gas may partially block the regenerator which increases the
amount of torque required to drive the displacer mechanism to the point
that the motor noise (ie:
ratcheting) may increase and result in coldhead
motor stalling.
3. Simultaneous
decontamination of
all On-Board
Cryopumps using
helium manifold Only one
On-Board
GLE
Cryopump
needs to be
cold. 45 minutes Acceptable
(may need to be
repeated in several
months).
Table 4-1: Methods of Decontamination
Method
Starting
Condition
Estimated Time
Effectiveness of
Decontamination