Electronic circuitry with self-calibrating feedback for use with an optical current sensor

Claim 1

A magneto-optical electrical current measuring system, comprising: a calibrated polarized light source, said light source being susceptible of low frequency variation in intensity; magneto-optical electrical current sensor means disposed to measure electrical current in an electrical conductor by magnetically modulating the polarization angle of polarized light passed therethrough in response to changes in said current, said polarized light coming from said polarized light source; circuit means connected to said magneto-optical electrical current sensing means for converting the modulated polarized light into a useful electric signal; and low pass filter means connected to the output of said circuit means for extracting therefrom that portion of said electric signal related to said low frequency variation in the intensity, the output of such low pass filter means being negatively fed back to said calibrated polarized light source for cooperating therewith to tend to reduce said low frequency variation in intensity to thus cause the intensity of said polarized light source to a constant value so that said modulated polarized light from said magneto-optical current sensor means tends to contain information only about said changes in said electric current.