Patent GB-667598-A (GB)
Title: Improvements in instruments for exploring electric fields
IPC: G01R29/08
Filed: 1950-01-20
Abstract: 667,598. Exploring electric fields. HIRBEC, L. L. J. Jan. 20, 1950, No. 1532/50. Class 37. An electric field exploring instrument comprises a rarefied gas-discharge tube having electrodes at least one of which surrounds an end thereof, an insulating sheath around the tube having at least a portion capable of letting light rays pass therethrough, and means for rendering the tube sensitive to potentials below the normal critical starting potential. A rarefied gas discharge tube 1, Fig. 1, is provided with end metal caps 2, 3 which slide on to the tube to form electrodes. The cap 2 has an axial aperture 2a to enable the glow at the end of the tube to be observed. A flexible sheath 4 of material such as polyvinyl chloride tightly surrounds the tube 1, the ends being extended to engage the electrodes 2, 3 so as to hold them resiliently. The sheath is provided with a sight aperture 5 and an elongated slot 6. A conducting strip 3a forms an extension of the electrode 3 within the sheath 4 to within a short distance of the electrode 2. The instrument is held in the hand through the electrode 3 and the electrode 2 is brought near a high voltage conductor. A glow discharge is then seen through the aperture 5 between the cap 2 and the end 3b of the strip 3a, and extends along the strip 3a as the electrode 2 is brought nearer. Several strips 3a may be provided starting from the same electrode 3. These strips may be separate from the electrode 3 but adapted to be connected therewith by conducting slides 3e, Fig. 2a, or the strips themselves may be mounted to slide and have an outer extension for manual control. One or more strips 3a insulated from the electrode 3 may also be connected by bridging portions passing through the sheath 4 to an outer conducting contact 3g, Fig. 2b, which is touched by a finger to start the discharge. The strip or strips 3a, the tube 1, or the sheath 4 may be provided with a scale, or the sheath may be provided with a series of cross slots instead of the apertures 5, 6 to provide a graduated scale. In a modification the extension of the electrode 3 is formed by a wire either parallel to the axis or coiled round the tube. The wire may terminate in a conducting surface of considerable area at the end near the electrode 2. The electrodes 2, 3 and auxiliary conductors 3a may alternatively be formed as conducting paints or deposits on the tube 1 or on the sheath 4, or they may comprise a material such as paper having metal on one or both faces. The sheath may be made of polyvinyl chloride and acetate polymers, polyvinyl acetals, polyethylenes, polystyrol, or acrylic resin, and may be transparent or translucent without side apertures, or opaque with transparent windows. In order to explore the electric field around a single wire, a T-shaped fitting 11, Fig. 14, is provided, the tubular portion 11a being slit at 11b so as to fit tightly on to the electrode 2. The portion 11c has a longitudinal gap 11d which is wide enough to allow the field-producing wire to be introduced. An end cap, which may be either conducting or insulating, may be fitted over the electrode 3 or the end of the sheath 4 and may have a sight aperture at its end.