Faraday effect current measuring device

Claim 1

In a current measuring device comprising a light source; a separator means for dividing the light emitted by said source into two light bundles; two optical paths disposed in parallel for said light bundles, each optical path comprising polarizer means, a Faraday effect rotator means subjected to a magnetic field produced by the current to be measured, and an analyzer means; photosensitive means for receiving the light bundles from said two optical paths and electrical circuit means for comparing the signals emitted by said photosensitive means in response to said light bundles; the improvement comprising a sheet of liquid crystal in each of said optical paths; and modulator means, connected to said liquid crystal sheets, for producing two pulse trains at the same frequency but out of phase with each other whereby the electric fields produced by said pulses cyclically change said liquid crystal sheets between transparent and opaque states such that only one of said liquid crystal sheets is in a transparent state at a time; and wherein said photosensitive means comprises a single photoelectric cell for receiving said two light bundles and a synchronized detector means, coupled between said photoelectric cell and said electric circuit means, synchronized with said modulator, for separating the signals from said photoelectric cell corresponding to said Two bundles, whereby the light bundles striking said photocell are a function of the output of said Faraday effect rotator means, the output of said Faraday effect rotator means being a function of the current causing the magnetic field which is the current to be measured.