Misuratore di livello di elio liquido

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Costruttore: American Magnetics, Inc., USA, 1991

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Descrizione e caratteristiche fisiche

The American Magnetics, Inc. (AMI) Model 110A Liquid Helium Level Monitor is an economical level meter designed for systems requiring a basic liquid helium level readout.

The Model 110A is designed to be used in conjunction with an AMI liquid helium level sensor. The liquid helium level sensor consists of a small diameter filament of NbTi superconductor, with a critical temperature Tc = 9.2 K, within a protective hollow tube. The liquid helium level sensor operates by measuring the resistance of the superconductive. A constant current is passed through this filament causing the portion of the filament in helium gas to become resistive (normal state), while the portion in the liquid helium remains in the superconducting state (zero resistance). The resulting voltage along the sensor is proportional to the length of filament above the liquid helium and provides a continuous measure of the helium depth.

Voltage measurements are made using a four wire technique to eliminate errors resulting from variations in the length of the leads. The small amount of heat generated in the probe is dissipated primarily in the helium gas rather than in the liquid helium. A standard sensor will not function properly through the lambda point.