GB439049A - Improvements in or relating to voltage measuring apparatus - Google Patents

Abstract

439,049. Pressure meters. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London, and MYERS, L. M., Roseberry, Cornfield Road, Middlesbrough. May 28, 1934, No. 15881. [Class 37] An instrument for measuring high voltages comprises two quartz laminµ Q, L, cut from oppositely handed optically active crystals, on the upper and lower faces of which are electrodes (not shown) to which the voltage to be measured is applied. These laminµ are arranged between a polarizer P and an analyser A, through which a beam of light from a source S is passed. A Fresnel double-wedge compensator F is situated between the laminµ Q, L and the analyser A, the optical system being adjusted to give a black band crossing the emergent beam from the analyser. The application of a potential difference to the electrodes causes a motion of the black band across the visible field proportional to the applied voltage. The instrument may be read by means of a telescope T provided with a scale, or an image of the beam may be projected on to a translucent screen provided with a scale. Alternatively the black band may be brought back to its original position by relative motion of the wedges of the Fresnel compensator F by means of a micrometer screw. The thickness of the quartz laminµ in the direction of the electrical axis may be of the order of a millimeter, the applied voltage being of the order of 30000 volts. For higher voltages mica or similar sheets may be placed on each face of the quartz and the electrodes mounted on the outer surfaces of the mica. The polarizer P and analyser A may be Nicol prisms or simple blocks of calcite. A screen D having a horizontal slit is provided to cut off the image due to the extraordinary rays.