GB517484A - Improvements in and relating to electrical measuring instruments - Google Patents

Abstract

517,484. Current measurements. BRITISH SANGAMO CO., Ltd., (Weston Electrical Instrument Corporation). July 29, 1938, No. 22627. [Class 37] The internal wiring of an instrument is arranged to afford protection against pick-up of stray currents from high-frequency alternating electric fields by forming the internal leads between the moving coil and the source of current therefor as a tubular conductor through which the other conductor passes. In the thermal ammeter shown a permanent magnet 2 is mounted on a base 1 and carries upper and lower bridges 5<1> on which the moving system is pivoted and through which the connections to the moving coil 3 are made. Massive metal blocks 6 carrying the heater 7 are carried by main terminals passing through the base 1. The hot junction of the thermocouple 10 is located at the midpoint of the heater 7 the cold ends being soldered to compensating strips 11, 11<1> carried at each end by the blocks 6 but insulated therefrom by thin mica sheets 12. A short tubular conductor 13 is soldered to the upturned end of the compensating strip 11 and to a bracket on the lower bridge. Passing through the tube 13 is a wire 15 soldered to the compensating strip 11' and a bracket 14 on the upper bridge 5', the wire being bent around the magnet 2 to reach the upper bridge. The soldered terminals of the strips 11, 11<1> are adjacent to each other and symmetrical with respect to a plane passing through the main terminals. The plane of the concentric conductors 13, 15 is normal to the current path through the heater 7 between the main terminals. In a modification the exposed portion of the central wire is reduced by arranging both the springs for making connection to the moving coil at one end of the coil.