High temperature conductor probes for determining liquid level of cryogens

A method of detecting the level of a liquid cryogen having a predetermined boiling point and held in a container which comprises:

• positioning a longitudinally extending, self-supporting, sensing member, composed of a high temperature superconductor material having a cross sectional area of A, a predetermined length L, a resistivity .epsilon. and a critical temperature that exceeds the boiling point of the liquid cryogen, vertically in a body of the liquid cryogen and normal to the surface of the liquid cryogen, said liquid cryogen being held in a container having a relatively flat bottom inner surface against which the lower end of said sensing member is maintained in contact;
• positioning a porous protective sheathing around the high temperature superconductor member so that the level of the liquid cryogen within the container penetrates said sheathing to surround said high temperature superconductor member and assume the same level within the sheathing as in the container and causing the portion of the sensing member below the level of the liquid cryogen to reach its superconducting state;
• passing an electrical current having a predetermined value through the length of the high temperature superconductor member;
• measuring the voltage drop across such member in response to the passage of electrical current therethrough;
• and
• determining the level of the liquid cryogen within the container according to the voltage drop measured across said high temperature superconductor member.