GB754151A - Improvements in or relating to electric resistance thermometer units - Google Patents

Abstract

754,151. Resistance thermometers. BAILEY METERS & CONTROLS, Ltd. March 26, 1954 [March 26, 1953], No. 8952/54. Addition to 751,398. Class 40(1) In an electric resistance thermometer which comprises an elongated corrosion and heat resistant metal sheath a temperature sensitive resistance coaxial with the sheath and formed of wire insulated therefrom by an insulating heat conductive filling or granular refractory material sealed in the sheath and leads extending from the ends of the wire within the sheath through opposite ends of the sheath, as described in parent Specification; gas tight extension sheaths are provided for enclosing lengths of the leads extending from the sheath. The main sheath assembly 24, is constructed as described in the parent Specification, the resistance wire being of Mb, and stainless steel extension sheaths 29, 30 are fitted over and welded to the ends of sheath 24. Extension leads 27, 28 which are welded to leads 25, 26 are contained within sheaths 35, 36 of refractory material, the outer ends of the extension sheaths being sealed in a gas tight manner by plugs 33, 34 which also insulate the sheaths from the extension leads. The whole assembly is purged of air and filled with protective gas, e.g. N 2 , by introducing the latter under pressure through one of'the two capillaries 31, 32 silver soldered through holes in the sheath, after which the capillaries are sealed off. Alternatively sheath 24 is first filled with gas suitable for protecting the Mb wire, sealed off and each extension then filled with another gas through capillaries 31, 32 after evacuation therethrough. The thermometer may form part of an automatic self-balancing measuring bridge as in the parent Specification. In the Fig. 4 arrangement adaptors 50, 51 are welded to sheaths 29, 30 and to plate 52 which is welded to and forms the end of a protective pipe 53 containing the sheaths. Outer and inner members 54, 55 of a pipe coupling welded to 53 co-operate with a mounting pipe leading, e.g. to a furnace. The other end of pipe 53 is coupled to a standard terminal box by adaptor 56. A further mounting arrangement for use where sheath 24 is in a high pressure chamber is shown in Fig. 5.