1. Field of the Invention
The present invention relates to a level gauge for detecting a level of liquid helium which is accommodated in a container made of metals, glasses or other materials. More particularly, the invention relates to a level gauge for detecting a level of liquid helium which uses, as a sensing element, a wire made of an amorphous superconductive alloy obtained by rapid by quenching a molten alloy. The level of liquid helium is detected by measuring an electric current, voltage and/or electric resistance of the sensor element.
2. Description of Related Technology
Liquid helium level gauges that use superconducting alloy sensing elements rely on the electrical resistance changes of the element to indicate liquid level. The portion of the element submerged in the liquid becomes superconductive, i.e. no resistance to electrical current. The portion above the liquid is not superconductive and resists electrical flow at a constant rate over its length. If the sensing element is homogeneous, has a constant width, and has a constant thickness, the resistance properties will be constant over the length of the sensor element. By passing an electrical current through the submerged element, measuring the electrical current, and comparing the value to a calibration relationship, the level of the helium can be determined.
In the level gauge disclosed in U.S. Pat. No. 4,655,079 (which is herein incorporated by reference), the superconductive alloy is represented by the following formula: EQU Zr.sub.100-x (Ru.sub.y Rh.sub.1-y)x
wherein x represents the contents of Ru and/or Rh in aomic % and has a numeral value of 22.5&lt;x&lt;27.5; and y represents a numerical value of 0&lt;y&lt;1.
However, the superconducting transition temperature (Tc) of that superconductive alloy ranges from 4.2K to 4.5K. This transition temperature is quite close to the temperature of liquid helium (4.2K). As the pressure in the storage vessel changes, the accuracy of the level measurements can decrease.