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2
Operation
Description and Specifications
E5084 - pressure regulation for twin cryogen magnets
10
The E5080 unit is available in two configurations. These
units are used to regulate the helium pressure within the
cryostats of conventional twin cryogen cryostats (E5084) and
refrigerated zero boil- off cryostats (E5083).
The twin cryogen cooled magnets are housed inside a helium
reservoir, which is supported from the neck turrets on the
top of the cryostat. These necks are in good thermal contact
with the cold gas which boils off from the helium reservoir.
Since the rate of cryogen boiloff inside a magnet cryostat is
influenced by the local atmospheric pressure, the necks
expand or contract a small amount when the pressure
changes and the flow of helium gas through the necks
changes. Since the magnet is hanging from these necks, it
moves up and down a small amount relative to the bore of
the cryostat.
For sites which experience large variations in atmospheric
pressure, the small movement of the homogeneous volume
with respect to the NMR sample volume can become
apparent. You can overcome this effect by isolating the
helium vessel from changes in atmospheric pressure, by
piping exhaust helium gas through the E5084 unit. The
E5084 actively regulates the flow of escaping helium gas so
that the pressure is kept at a constant set level, typically a
little higher than the maximum local pressure which will
generally be experienced.
E5080 Series Cryogen Monitor User Guide
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