GB644998A - Improvements in thermal responsive electric switches of the glow discharge type - Google Patents

Abstract

644,998. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd., and SCOTT, W. J. April 3, 1947, No. 9084. [Class 38 (v)] [Also in Group XIII] In a glow-discharge switch use is made of the effect of the local flow of heat in the bimetallic element or elements (see Group XIII) to prolong the period in which the contacts are closed. In Fig. 2 a U-shaped bimetallic strip 5 has its longer limb secured to a support 6 of good heat conductivity. When the glow discharge heats the element it distorts into the position shown by dotted lines 10 to close contacts 8, 4. Due to the more rapid loss of heat from the longer limb than from the shorter limb 7 when the discharge ceases, the former tends to return to its original position first and by so doing, prevents the immediate re-opening of the contacts. Fig. 4 and Figs. 5-7 (not shown) illustrate modifications in. which the shorter limb 12 of a U-shaped element is fixed to the support, the " U " being formed by cutting rather than bending a bimetal strip into that shape. In other modifications the bimetallic element may be formed by twisting a strip through 180 degrees near its supported end, Fig. 8 (and Fig. 9, not shown), or by welding the ends of two bimetallic strips together so that the two portions of the element tend to deflect in opposite directions. The two strips may be of different pairs of metals or of different thicknesses. Two co-operating bimetallic elements similar in shape to the element of Fig. 2 may also be used, Figs. 12, 13 (not shown). Specification 537, 901, [Group XL], is referred to.