GB966300A - Electrical power measuring apparatus - Google Patents

Abstract

966,300. Power measuring. J. F. S. CARRUTHERS, and W. WILSON. Nov. 24, 1961 [Nov. 4, 1960], No. 38075/60. Heading G1U. [Also in Division G4] Power measuring apparatus comprises a capacitive voltage divider across spaced conductors supplying the power to be measured, a semiconducting Hall effect member "energized" from said voltage divider, and also intersected by the magnetic field created by current flow in said conductors, the resulting Hall voltage being representative of the product of voltage and current in said circuit. In one embodiment Figs. 1, 2 the lower of the spaced conductors 10, 11 is earthed and carries on a post 13 a brass Faraday screen 12 within which the Hall plate 27 is mounted with its plane normal to the magnetic field produced by current in the conductors 10, 11. The voltage divider is formed by two series connected capacitors. One capacitor is formed by an earthed plate 19, a dielectric disc 23 silvered on both sides and a disc 21 carried by a pin 22. A further smaller capacitance exists between disc 21 and a conductor 10, this capacitance being varied by altering the size of an aperture 25 in an intervening plate 24 secured as is plate 19 to the earthed screen 12. Lead 26 connects the Hall plate across the first capacitor. The Hall voltage is led out via leads 29, 30 to a shielded cable 31, and thence to a watt-meter. The screen 12 is slotted as shown to minimise eddy-current flow therein. A further R. F. embodiment employs a potentiometer 50, Fig. 3, to balance the Hall plate 45 so that there is no P.D. between connections 52, 53 in the absence of a magnetic field. The Hall output voltage is smoothed by capacitors 55, 58, and R.F. chokes 64, 65. The construction adopted, Figs. 4, 5 (not shown) is substantially the same as that of Figs. 1, 2 except that an outer cylinder is provided which encloses the screen and the associated portion of the live conductor 42. To ensure that the magnetic field and the energizing current are substantially in phase the H.T. lead from the Hall plate to the voltage divider may in either embodiment be connected via a transistor biased to render the transistor conducting in operation.