Hi Pedro,
Back when we were developing the Stanford Automouting robot,
I ran several tests with thermocouples mounted in Hampton Cu Pins
and loaded into SSRL cassettes. These were placed in a shipping
dewar and the temperature at the bottom and top of two stacked cassettes
was monitored over time as the dewar charge ran out. I don't
have the data in front of me to review, my my recollection was that
the temperature in the cassette was pretty constant throughout the
entire working / holding time of the dewar and it was not until the
end of the hold time that the temperature ramped up.
We did not see a significant temperature gradient between the bottom and
top cassette, something like ~2-4 K. (Each SSRL cassette is 130 mm, so the
top to bottom height difference is on the order of 235 mm for the two pins
and the top pin is ~247 mm from the the bottom of the canister and
the bottom of the top cassette is 130 mm from the bottom of the canister).
https://smb.slac.stanford.edu/facilities/hardware/cassette_kit/Cassette-Al-6-MD6-021902.pdf
This is not quite the same as trying to measure the temperature of the air
in the dewar just below the neck tube and comparing it to the temperature
at the bottom.
We also tested taking sample cassettes out of the shipping dewar and
sitting them on the bench. It would take on the order of 3 min for the
temperature of the thermocouple pin in the cassette to warm to ~123 K.
Regards,
Mitch
Quoting Pedro Matias <[email protected]>:
My thanks to Mitchell and Artem for their replies and suggestions.
Our dewars are all CX100.
We are using the weighing method but my concern is that the
temperature at the top of the dewar can reach above 150K even with
some LN2 present, which can lead to the recrystallization of the
amorphous ice, so I am aiming to establish a correlations between
LN2 weight in the dewar and its temperature, especially in the top
region.
About regenerating the vacuum, our CX100 dewars are all imported and
I am not aware of any local representative offering this service. My
feeling is that they'd rather sell you a new one.
Best regards,
Pedro Matias
On 18/10/2024 13:23, Pedro Matias wrote:
Dear All,
I'm looking for a low temperature measuring system to check our dry
dewars, preferably one that is not very expensive. Any
recommendations ?
Also, I was told that it is possible to regenerate the vacuum in
those vessels. Does anybody have any experience with this? If so,
how can it be done?
Thanks in advance,
Pedro Matias
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