GB159203A - - Google Patents

Abstract

159,203. Lederer, A. Feb. 25, 1920, [Convention date]. Indicating, optical devices for; index hands.-To increase the sensitiveness of hot-wire instruments depending upon the expansion of the wire, the hot wire is supplied with an independent heating-current from a separate source, upon which the current to be measured is superposed without initial interference of the current sources. As shown in Fig. 2, two hot wires 2, 3 are arranged in parallel between terminals 4, 5 by means of which they are supplied with current from a battery 6. Levers 7, 8, mounted on steel blades 9, 10 forming the armatures of magnets 11, 12, engage the hot wires 2, 3. Spring wires 15, 16 conveying the current to be measured are joined to, but insulated from, the levers 7, 8, and make electrical contact with the wires 2, 3 at their central points, so as to form a wheatstcne-bridge connection. Relative motion of the levers 7, 8 is indicated by a steel mirror 19 carried by short magnetic steel blades 17. 18 on the ends of the levers 7, 8. In a modification, Fig. 4, a number of hot wires 1 - - 6 are arranged in a circle between two conducting plates by means of which the independent heating-current is introduced. The centres of the hot wires are connected alternately by springs 26 to wires 34, 35 by which the current to be measured is introduced. The springs 26 expand a resilient ring 27, open at one place, relative motion of the ends of the ring being communicated by links 28, 29 to a lever 30 carrying a pointer 31. Other mechanisms may be used for indicating the expansion of the ring 27. A regulating-resistance may be inserted in the heating-current circuit to enable the pointer to be brought to zero.