66 (93) BRUKER CryoProbe Installation
Troubleshooting
Cool-down doesn’t reach cold state 5.3.5
The cool-down procedure must have reached the cold state within 4 h, otherwise
a warm-up is initiated automatically. After the system has warmed-up completely,
press
COOL DOWN again.
Did the message
Warm-up needed soon appear recently? If yes, see “Warm-up
needed soon request” on page 63 in the User Manual.
Adjusting the He flow
IMPORTANT: He flow adjustments at the CryoCooling Unit are sometimes coun-
ter-intuitive but always time consuming. Do not change any setting without explicit
advice from B
RUKER.
When cooling down a CryoProbe System for the first time, the flow of cold He may
not be adjusted in an optimum fashion for the given environment, e.g. if the Cryo-
Cooling Unit was tested at a different mains frequency and voltage settings.
The overall He flow is factory-set at the (warm) throttle valve R1. It is interesting to
note that a higher flow does not necessarily result in a better cooling. Thus, there
is an optimum position that is different from ‘completely open’.
Balancing is done at the cold (!) throttle valve V16 which is located inside the Cry-
oCooling Unit below the big cylindrical vacuum chamber. It carries a 360° scale
and is closed by turning to the right, i.e. towards increasing values. This valve
must not be operated when the CryoProbe System is cold.
Example:
the ‘Preamp’ temperature is too low and cannot be increased even by
100% Preamp-H6 heater power.
Quick’n’dirty fix:
reduce the overall flow while the system is in cold operation by
closing R3: Mark the actual position of R1. Turn R1 in steps of quarter-turns and
allow at least 10 min for equilibration.
Permanent solution:
Close V16 in steps of half-turns with R3 being in its original
position. Since V16 must not be operated when cold, each adjustment involves a
full warm-up/cool-down cycle. To obtain reproducible results, close V16 first com-
pletely, the open it by the desired number of turns. After each change, cool-down,
and equilibration for ½ - 1 h, write down the resulting Insert and Preamp tempera-
tures to assure that the process goes into the right direction.
1.12 Close and open V7 five times for a few seconds. Switch OFF the DRIVE
of the ColdHead.
1.13 Close the relief valve of the large DumpTool compleatly and close all
valves (V4 and V8 are normally open!).
1.14 Repeat steps 1.7 and 1.8.
1.15 If the characteristic hiss can still not be heard, then the ColdHead
needs to be replaced.
step action
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