Abstract
The circuit of the level indicator is illustrated. An automatic reduction nnn bridge sensitivity was provided in order to achieve a greater decrease in the reverse current on lifting the probe out of the liquid helium vessel. The tantalum sensitive resnnstance and the nickel ballast resistance are made in the form of 1.5 mm spirals. The liquid helium level is determined by lowering the probe slowly into the vessel. The approach of the milliameter needle to the zero division shows that 40 to 50 mm remain before the surface of the liquid. The moment at which the sensnn-tive element is immersed in liquid is fixed very clearly. The tantalum wire heats up rapidly to above 4.3 f K on raising the probe out of the liquid, and after l to 2 sec the instrument is ready for a repeat measurement. (P.C.H.)
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