American Magnetics AMI Liquid Helium Level Sensors - Manual (Page 2)

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AMI
EXCELLENCE IN MAGNETICS AND CRYOGENICS
III. INSTALLATION
A. Carefully remove the sensor from the shipping tube and remove all packaging
material.
NOTE: If there is any shipping damage, save all packaging material
and contact the shipping representative to a file a damage claim. Do not
return the instrument to AMI unless prior authorization has been
received (refer to Section VIII).
B. The sensor must be mounted with the electrical leads at the top.
C. For minimum losses, mount the liquid helium sensor so that warm helium gas rising
from the sensor can pass directly out of the dewar without contacting surfaces at 4.2K.
Do not mount the sensor in restricted areas (tubes, etc.) where the liquid level around
the sensor might be depressed by pressure differences in the gas. Do not cover the
holes in the sensor.
D. The sensor may be mounted by taping or clipping it to an appropriate support
structure. Do not exert excess pressure on the sensor with the mounting device to
avoid crushing the tube. Avoid constraining both ends of the sensor and allow for
contraction of the sensor during cooldown.
NOTE: Avoid bending the sensor or lead wires when cold to avoid the
possibility of cracking or breaking the sensor or wire insulation.
CAUTION: Do not operate the sensor in a vacuum. Operating the
sensor in a vacuum may cause thermal damage and/or destruction of
the superconducting filament sensor. Do not inadvertently turn the
instrument on with the sensor in an evacuated chamber. Operation in
pumped liquid helium environments is acceptable to 1K as long as
liquid helium is present.
E. Avoid installing in a location where icing (frozen water or gas) may occur since ice
formations may cause erratic operation. Ice formation on the NbTi filament may stop
the propagation of the normal (resistive) zone before it actually reaches the liquid/gas
interface. This will give an indication of a higher helium level than actually exists.
F. Ensure the level meter is de-energized (unplugged) and connect the sensor to the
meter. The liquid helium level sensor leads are color coded:
Red ...... I +
Blue ...... V +
Yellow .... V -
Black ..... I -