Bruker RS, Service Manual, Page: 76 / 157

76 ZTKS0156 / Z31820 / Rev.: 03
Assembling
36. Check at the high and low pressure gauges on the compressor front panel if the
mean values are different and if an oscillation of the needles is noticeable. This
difference will decrease as the cold head cools down.
The typical pressure difference are approximately:
50 Hz compressor: 14.5 to 16.5 bar (210 to 240 PSI) with a 0.34 to 0.7 bar
(5 to 10 PSI) amplitude on the needles.
60 Hz compressor: 14.5 to 16.5 bar (210 to 240 PSI) with a 0.34 to 0.7 bar
(5 to 10 PSI) amplitude on the needles.
For further information refer to the supplied manual of the Cryogenic Refrigerator.
37. Check the two PT 100 temperature sensors for monitoring the cooling down.
38. The ACD will stop the liquid nitrogen transfer automatically at a temperature of 80 K
to prevent the accumulation of liquid nitrogen inside the helium vessel. The
magnet’s temperature monitored with the two PT 100 temperature sensors should
be between 80 K and 90 K.
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In case of cooling down without Automatic Cooling Device (ACD):
- connect the two PT 100 temperature sensors to a measuring device (not supplied)
- check the PT 100 temperature sensor: temperature difference between upper and
lower temperature sensor maximal 25 K. Adjust the cooling speed with the liquid
nitrogen flow.
- stop liquid nitrogen transfer at a temperature of 80 K at the lower PT 100 temperature
sensor.
39. Switch off the ACD and remove the connection to the liquid nitrogen transportation
dewar at the precooling tube (5).
40. Remove the one way valve (2) from the helium flow system and connect the
nitrogen gas transportation dewar to the helium flow system.
41. Blow in nitrogen gas with a pressure of 0.1 - 0.15 bar (1 PSI) and check if liquid
nitrogen spills out of the precooling tube (5). In case of liquid nitrogen spilling out
warm up the system to 90 K to make sure that no liquid nitrogen is left inside the
helium vessel.
42. Check the temperature of the PT 100 temperature sensors.
43. Remove the nitrogen gas transportation dewar at the helium flow system and
remount the one way valve (2).
44. Connect the precooling tube (5) to a pressure gauge.
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Keep the helium flow system closed at all times if the cryostat is below room tem-
perature to prevent moisture entering the helium vessel. If necessary open the helium
flow system as short as possible. Do not open both helium turrets simultaneously.
Keep the cold head turret pressurized at all times if the cryostat is below room tem-
perature.