US 4,904,931 A · Electro-optical voltage measuring system incorporating a method and apparatus to derive the measured voltage waveform from two phase shifted electrical signals

Abstract

The voltage between two objects is measured utilizing an electro-optic crystal exhibiting birefringence in two axes (slow and fast) mutually orthogonal to an optic axis extending between the two objects. Two collimated light beams polarized at an angle to the slow and fast axes is passed through the crystal parallel to the optic axis with one of the collimated light beams retarded relative to the other by about 1/4 wave. The two beams emerging from the crystal are passed through a polarizer and converted to phase shifted electrical signals by photo diodes in electric circuits which regulate the sources of the light beams to maintain the peak magnitudes of the two electric signals constant and equal. As another feature of the invention, a stairstep output waveform representative of the measured waveform is generated in a digital computer from a bidirectional cumulative count of zero crossings of the two electric signals which is incremented or decremented depending upon which of the two electrical signals is leading. Improved accuracy of the output signal is achieved by adjusting the stairstep waveform by the magnitude of the smaller of the two electrical signals, with the sense of the adjustment determined by the relative polarities of the two electrical signals.

Claims18

Dependent claims

Apparatus for measuring an electric potential between two spaced apart objects, said apparatus comprising:

light source means generating collimated light;
first polarizing means polarizing said collimated light to form polarized collimated light;
an electro-optic crystal having a fourfold axis of rotary inversion extending between said spaced apart conducting objects, said polarized collimated light passing through said electro-optic crystal in a direction parallel to said fourfold axis of rotary inversion;
fractional waveplate means through which at least a first portion of said polarized collimated light passes after passing through said crystal, said fractional waveplate means retarding said first portion of polarized collimated light about an odd multiple of 1/4 wave with respect to the second portion of said polarized collimated light;
second polarizing means through which said first and second portions of said polarized collimated light pass after passing through said crystal and said at least one portion thereof passes through the fractional waveplate means;
first and second detectors converting said first and second portions of said polarized collimated light emerging from said second polarizing means into first and second electrical signals respectively;
and
output signal generating means for generating an output signal representative of the potential between said two spaced apart objects from said first and second electrical signals.

5 more elements

A method of measuring electrical voltage between two spaced objects comprising the steps of:

positioning an electro-optic crystal exhibiting birefringence in two orthogonal axes transverse to an optical axis in response to an electric field, with said optical axis extending between said two objects;
generating collimated light polarized with a selected plane of polarization;
passing the polarized collimated light through said crystal parallel to the optical axis and with the plane of polarization of the polarized collimated light at a selected angle to said two orthogonal axes of the crystal;
retarding a first portion of said polarized collimated light emerging from said crystal with respect to a second portion;
passing the two portions of polarized collimated light after the first has been retarded relative to the second through polarizing means;
converting the two portions of said polarized collimated light as they emerge from the polarizing mean into first and second phase shifted electrical signals;
and
generating an output signal representative of the voltage between said two spaced objects from said two phase shifted electrical signals.

5 more elements

Dependencies are inferred from the claim text.

Electro-optical voltage measuring system incorporating a method and apparatus to derive the measured voltage waveform from two phase shifted electrical signals

Life of this patent

Electro-optical voltage measuring system incorporating a method and apparatus to derive the measured voltage waveform from two phase shifted electrical signals

Life of this patent

Abstract

Claims18