GB1089966A - Thermo-electric devices - Google Patents

Abstract

1,089,966. Thermoelectric devices. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 23, 1966 [Feb. 23, 1965], No. 7861/65. Addition to 1,089,781. Heading H1K. [Also in Division G1] In a multi-junction thermoelectric converter according to the parent Specification, a generally triangular section helix having a rod-like support along each apex has the supports secured to the helix by an epoxy resin or other electrically insulating cement which will withstand temperatures of up to 240‹ C. In one method of making the device the first step is to secure a twisted loop of wire 53, an enamelled wire 57 and a tinned copper wire 58 in parallel relationship on a polystyrene sheet 56 by means of polystyrene cement. The sheet is then fixed to a triangular section polystyrene core 52 so that the twisted loop 53 is disposed along one apex, a thin mica strip 55 is cemented to the core adjacent a second apex, and a further twisted loop 59 (not shown) attached to a second sheet of polystyrene is cemented along the third apex. Constantan wire 51 is then wound tightly on the core at 200 to 300 turns to the inch and epoxy resin cement capable of withstanding temperatures of up to 240‹ C. is applied as at 63 to bond the twisted loops 53, 59 to the helix. A guide wire 62 may be employed to facilitate the application of the resin, the wire being subsequently removed when the resin has set. A thick polystyrene sheet 64 carrying a tinned copper strip 65 is secured to the helix with polystyrene cement to cover the region between the enamelled wire 57 and the twisted loop 53 and the whole assembly is immersed in a plating bath to deposit copper on the exposed portion of the helix. During plating current is supplied to the helix through the wire 58 and strip 65. After cleaning, the mica strip 55 is secured to the helix with epoxy resin cement and all the polystyrene is dissolved away, thereby freeing the wires 57, 58 and the strip 65 and leaving the helix firmly bonded to the twisted loops 53, 59 and the mica strip 55 which form the three supports. The finished helix may then be mounted in an evacuated copper box (Figs. 6 and 7, not shown) lined with sheets of aluminized mica, the box being baked at 200 -220‹ C. during the evacuation. The device is employed in measuring A.C. currents at audio and high frequencies or as a high-frequency wattmeter, the twisted loop 53 being the heater which carries the current to be measured. A differential converter may be made by using the twisted loop 59 as a second heater and plating the helix so that the side between the loops 53 and 59 is bare. Monofilar heaters may be used in place of twisted loops. The thickness of the copper coating is preferably selected so that the temperature coefficient of the converter is substantially zero and the output is a maximum for a given input current.