134
CHAPTER 6:
Maintenance and Troubleshooting
Model CRX-6.5K Probe Station
6.2.11.4 Diaphragm Pumps
On smaller probe stations, diaphragm pumps can be used as fore pumps for the turbo
pump; however, even on smaller probe stations, the seals in the pump wear down and
should be replaced periodically. Always follow the manufacturer’s recommendations
to reduce potential down time.
6.2.12 Removing
Condensation from
Inside the Vacuum
Chamber
Opening the vacuum chamber to atmosphere when the sample cooling assembly is at
cryogenic temperatures allows water vapor to condense on the probe station and
freeze into ice. It is possible for the probe station or turbo vacuum pump to suffer
irreparable damage when this occurs. It can take as long as a week to return the probe
station to proper working order. The time is required because water molecules are
easily attracted to the surfaces inside the probe station, such as the convolutions in
the bellows, and it is difficult for the vacuum pump to remove them.
To dry out the vacuum chamber and check for damage, follow this procedure:
1. If the sample cooling assembly is still cold, close the purge valve and vacuum iso-
lation valve to prevent more moisture from entering the system.
2. Turn off and properly vent the turbo pump. The turbo pump should not be used in
this process until all visible water has evaporated from the chamber.
3. Allow all stages to warm to room temperature (300 K). The temperature control-
lers can be used for warm up, but they should be monitored closely in case any of
the sensors were damaged.
Never heat any part of the probe station sample cooling assembly above room
temperature unless the vacuum chamber is under vacuum.
4. Remove the chamber and radiation shield lids and sample holder.
5. Wait 24 h to 48 h for the system to dry until there is no visual condensation on
the inside or outside of the vacuum chamber. A small fan or heat lamp may speed
this step.
6. Reinstall the sample holder, radiation shield lids and vacuum chamber lid.
7. Perform the heated cycle purge of the vacuum chamber as outlined in
section 5.2.1.1. The initial pump down may take longer than normal due to water
molecules still trapped in the vacuum chamber. An initial overnight (12 to 24 h)
pump down is recommended.
When warming the stages, be sure to monitor the stage temperatures closely until
they stabilize in case any of the sensors were damaged.
8. If the station can attain <10
-3
Torr, then go on to step 9; if not, contact the
Lake Shore service department because the system may have a vacuum leak or
other damage.
9. Use the procedures in section 3.8 to ensure basic functionality of the probe sta-
tion and vacuum pump.
