GB862047A - Improvements in load current meters - Google Patents

Abstract

862,047. Current measurement; measuring instruments. SANGAMO WESTON Ltd. June 21, 1957 [June 22, 1956], No. 19639/57. Class 37. A load 10 (e.g. the motor of a machine tool) is connected to an A.C. source 11 through the primary of a current transformer 16 whose secondary is connected across a first diagonal of a modulator bridge 21 comprising four series assisting copper oxide or thermionic half-wave rectifiers 21-24. Adjustable and centre tapped potentiometers 32, 28 are connected across the first and second bridge diagonals, and their tappings are connected to the A.C. source through a limiting resistance to derive a polarizing voltage which on alternate half cycles drives alternate pairs of rectifiers 21, 23; 22, 24 to cut off and to conducting saturation respectively. A D.C. meter 33 is connected to the bridge through a variable potentiometer 34 in parallel with potentiometer 28, and is traversed by a unidirectional pulsating current of which the excursions are coincident with successive A.C. half cycles and which is shown to be proportional in amplitude to the in-phase component of the load current. Potentiometer 34 is adjustable to vary the sensitivity and particularly to set the meter full scale deflection to indicate maximum load current. Potentiometer 32 is adjustable to balance out the inphase current when the load is in an idling condition so that the meter reads zero and is able to indicate directly the working values of in-phase current.