GB274575A - - Google Patents

Abstract

274,575. Rickets, W. J. April 24, 1926. Electromagnetic current and pressure meters; power meters.-In an electric measuring instrument the torque produced by the reaction between the currents passing through the coils of a system is balanced and the removable coil brought back to zero position by a magnetic field due to a direct current, the measure of which gives the indication required. Fig. 1 shows an electrodynamometer having a fixed coil 1 and a moving coil 2. Attached to the moving coil 2 and rotatable coaxially therewith is the movable element 3 of an ammeter or galvanometer of any type, shown as a coil moving in the field of a permanent magnet. Alternatively an iron member of permanent magnet may move in the field of a fixed coil system. In a modification, the moving coils 2, 3 are mounted on separate axes, preferably parallel, which carry light yokes connected by thin threads or otherwise. To operate the instrument as an ammeter, for example, the current to be measured is passed through the coils 1, 2 and a direct current is passed through the coil 3 and adjusted until the resulting torque balances that due to the interaction of the coils 1, 2, so that the system is brought back to zero. The current passing through the coil 3 is a function of the current to be measured. The instrument may similarly be employed as a volt meter or wattmeter. Fig. 3 shows ar alternating-current wattmeter in which a single moving coil 2 is employed both as an alternating current pressure coil and a control coil supplied with direct current from a battery 15. A choking-coil 12 prevents appreciable flow of alternating-current in the direct-current circuit and a condenser 8 prevents direct current from entering the alternating-current circuit. The moving coil 2 is situated in the magnetic field of a permanent magnet 16, Fig. 4, with laminated pole-pieces 17. Two fixed coils 1, 1<a> are pro vided as the equivalent of the coil 1, Fig. 3, and are arranged to yield a narrow but intense field cutting the vertical parts of the rectangular moving coil 2, which are situated at a relatively great distance from the axis to increase the torque. The magnetic path may contain iron The moving coil 2 may be replaced by an astatic combination of two coils 2b, 2<c> as shown ir Fig. 6. '