Patent GB-671734-A (GB)
Title: Improvements in or relating to electric circuits
IPC: F24H1/12
Filed: 1950-03-01
Abstract: 671,734. Wire resistances; resistance casings; thermoelectric batteries. PYROMETRIE INDUSTRIELLE. March 1, 1950 [March 1, 1949], No. 5211/50. Classes 37 and 53. [Also in Group XI] A resistance or thermocouple is placed between two metal plates which have been treated on one side so as to obtain a salt or oxide of the metal forming a thin insulating film, a high mechanical pressure being applied to the plates. A low thermal inertia is obtained owing to the very small thickness of the insulating layer and to the intimate contact produced by the high pressure. The metal plates may be of aluminium or magnesium, or plates of other metals or their alloys, and are coated with very thin films of oxide or salt of the metal forming the plate. The layer of oxide or salt may be formed electrolytically. A heating resistance strip 1, Fig. 2, is helically wound around a cylinder 3, the external surface of which is coated with an insulating layer. An outer cylinder 2, having its inner surface coated with an insulating layer, is shrunk on hot, or alternatively the inner cylinder may be cooled. Connecting leads 11, 12 are brought out through apertures in the inner cylinder 3, the edges of which are also coated with insulating layers. In a modification, Fig. 3, the connecting leads are soldered to brass or copper rings 13, on to which the inner cylinder 3, provided with insulating layers on both faces, has been shrunk hot. The cylinder 3 is provided with shoulders 14 of the same height as that of the resistance strip 1, so that when the outer cylinder 4 is shrunk on the annular space 15 is rendered fluid-tight. This space may be evacuated or filled with a neutral gas. The resistance strip 1 may be iron carrying a current such that it is at the critical temperature beyond which its resistance suddenly increases. The current strength is then maintained constant. The connecting leads may alternatively be brought out through apertures in the outer cylinder. Fig. 5 shows a resistance probe for measuring temperatures. The resistance wire 1 is held between cones 3, 4 so that high pressure can be produced between them without shrinking the outer cone 3 on hot. The wire 1 is of metal sensitive to temperature, e.g. nickel, platinum, or copper and is connected to a Wheatstone bridge by a cable 21. Fig. 6 shows a cylindrical arrange. ment comprising a heating element and one or more thermo-electric couples. The heating element is formed by a resistance wire 1 between two cylindrical plates 3, 4. One or more thermo-electric couples, 25, 251, 25<SP>11</SP>, 25<SP>111</SP> are held against the internal surface of the plate 4 by cylindrical plates 31, 32 so that the hot junctions 26, 26<SP>1</SP>, 26<SP>11</SP>, 26<SP>111</SP> located on one and the same circle are heated by the resistance 1. The couples are connected in series, their cold junctions 27, 271, 27<SP>11</SP>, 27<SP>111</SP> being arranged in a circle but outside the heating influence of the resistance 1. The whole is enclosed in a casing 28 with a cover 29. Lagging 30 isolates the resistance 1 from external influences. The device may be immersed in fluid flowing in the direction F, the E.M.F. generated by the thermo-couples varying-according to the speed of flow. Fig. 7 shows a temperature-sensitive resistance 1 arranged between two plane plates 3, 4, the inner surfaces of which are coated with insulating layers. For measuring the temperature of a press plate 31 the unit is pressed against this by a plate 33 bolted thereto, with the interposition of a thermally insulating sheet 32. In another construction, Fig. 9, the plates 3, 4 are bent into cylindrical form and pressed together by bolts 34. In the form shown in Fig. 11 the plates 3, 4 are curved and held together by tenons 37, 38, on the plate 4 engaging holes 44, 45 in the plate 3. The assembly is fixed to a frame 39 by claws 40, 41 and bolts 42, 43. The plate 3 is heated until the tenons 37, 38 coincide with the holes 44, 45 so that on cooling the plate 4 is compressed and the plates 3, 4 are forced into thermal contact with the resistance 1.