ELECTRO-OPTICAL VOLTAGE MEASURING SYSTEM INCORPORATING A METHOD AND APPARATUS TO DERIVE THE MEASURED VOLTAGE WAVEFORM FROM TWO PHASE SHIFTED ELECTRICAL SIGNALS

摘要

The voltage between two objects is measuredutilizing an electro-optic crystal exhibiting birefringencein two axes (slow and fast) mutually orthoganal to an opticaxis extending between the two objects. Two collimatedlight beams polarized at an angle to the slow and fast axesis passed through the crystal parallel to the optic axiswith one of the collimated light beams retarded relative tothe other by about 1/4 wave. The two beams emerging fromthe crystal are passed through a polarizer and converted tophase-shifted electrical signals by photo diodes in electriccircuits which regulate the sources of the light beams tomaintain the peak magnitudes of the two electric signalsconstant and equal.As another feature of the invention, a stairstepoutput waveform representative of the measured waveform isgenerated in a digital computer from a bidirectionalcumulative count of zero crossings of the two electricsignals which is incremented or decremented depending uponwhich of the two electrical signals is leading. Improvedaccuracy of the output signal is achieved by adjusting thestairstep waveform by the magnitude of the smaller of thetwo electrical signals, with the sense of the adjustmentdetermined by the relative polarities of the two electricalsignals.