GB1481263A - Apparatus for measuring current flow - Google Patents

Abstract

1481263 Measuring current APPLIED POWER AUSTRALIA Ltd 25 Sept 1975 [26 Sept 1974] 39340/75 Heading G1U In measuring current a magnetic core having more than one magnetic path one part of which contains an air-gap for preventing saturation, the gap being capable of temporary widening to permit encircling of a current-carrying conductor, and the output of an oscillator including windings wound on another part of the core is affected by flux caused by the current flow. The conductor Ls produces a unidirectional flux linking the coil pairs 18a, 18b and 19a, 19b. The part of the magnetic circuit encircling the conductor has an airgap which prevents magnetic saturation, but the windings 18-19 are wound such that the oscillator formed by transistors 31, 33 saturates the other part of the core. Transistors 32, 34 are provided such that for a zero current in L 5 , the oscillator output Fig. 3 (not shown), is symmetrical about zero and the transistor switch 35 thus provides a 1:1 mark/space ratio output. The uni-directional flux due to Ix in L 5 creates a D.C. shift in the oscillator output which changes the mark/space ratio, which can then be measured. Providing its frequency relative to the oscillator frequency is low, A.C. can also be measured.