| Popis: |
Superconducting-coil systems are usually contained in metal dewars so that the liquid helium level cannot be viewed directly. The liquid level can be monitored at fixed points by means of various level detectors [1–4]. However, a simple detector which can give a continuous indication of liquid level is more desirable than fixedpoint detectors. A linear liquid helium level detector which uses a superconducting element of annealed Ta [5] and another using a Pb-Sn [6] alloy element fulfill the requirement of simplicity ; however, neither of them can be expected to work except in very low magnetic fields. Another linear detector which relies on the measurement of the small capacitance difference between liquid helium and gaseous helium [7] should work in a magnetic field ; however, the associated electronics is complicated and the system must be constructed with great care. |
