| 摘要 |
<p>1,099,409. Liquid level indicators. SOCIETE INDUSTRIELLE DE LIAISONS ELECTRIQUES. Feb. 10, 1965 [Feb. 25, 1964], No. 5760/65. Heading G4H. [Also in Division G1] A semiconductor element 2, Fig. 1, having a very high inverse temperature coefficient of resistivity is used to determine the level of a liquefied gas by applying a fixed voltage to the element and measuring the current increase resulting from thermal runaway as the element crosses the liquid boundary. The normal current tends to heat the element, which may be carried in a stainless steel tube 10, and having reached an equilibrium value when the element is immersed in the liquid, the current increases by a large amount when the element passes into the vapour phase above the liquid, on account of the lower thermal conductivity of the vapour, which causes the current to heat the element to a higher temperature. This reduces the resistance further and causes the constant voltage source to supply an even larger current, the effect being cumulative until a new equilibrium is reached at a much higher current value. Several elements at different depths may be used to control a valve supplying liquid to a container, in order to stop the inflow when a desired depth is reached. The element may be made of silicon doped with boron, and a limiting resistor 6 may be included.</p> |
