GB235746A - - Google Patents

Abstract

235,746. Good, W. B. Aug. 12, 1924. Thermal current meters; temperature errors, compensating for.-The main current terminals a, b of a thermal ammeter are connected by a heating strip or wire c to which is thermally connected the hot junction d of the main thermoelectric couple d<1>, d<2>, the connection preferably being made through a short length of wire c<1>, serving only as a heat conductor. ' The cold ends d<3>, d<4> of this couple are each connected to the galvanometer e by means of subsidiary or compensating thermo-electric couples f<1>, f<2> and g<1>, g<2>. The hot junction f<3> of the couple f<1>, f<2> is connected to a compensating-plate h which is thermally connected to the terminal b but electrically insulated therefrom, as by a sheet of mica i. Similarly, the hot junction g<3> of the couple g<1>, g<2> is connected to a plate j which is thermally connected to but electrically insulated from the terminal a. The wire d<1> may be iron and the wire d<2> eureka, the wires g<1>, f<2> being of copper and the wires f<1>, g<2> of constantan. The ptates h, j may be of copper or other metal. The same materials may be used in the compensating couples as in the main couple, provided they are arranged to produce a reverse current from that due to the main couple.. The current generated by the compensating couples is equal to that generated by the main couple after the main circuit current is broken, thus bringing the indicating needle rapidly to zero. The indicatoris calibrated to allow for the reverse current generated in the compensating couples.