GB648583A - Improvements in or relating to electric condensers - Google Patents

Abstract

648,583. Variable condensers. BOSWELL, I. I., and PLANER, G. V. Nov. 15, 1948, No. 29671. [Class 37] In a condenser with a solid dielectric having opposed wall surfaces in contact with separate electrodes of the condenser, at least one electrode being a conductive liquid, e.g. mercury, in a container and in which the capacitance is varied by immersion of a solid body into the liquid, thereby displaced to contact a variable area of the dielectric, the latter comprises a ceramic material having a high dielectric constant such as fired titanium dioxide, fired barium titanate or other compounds of the perovskite type, and means are provided to exclude atmosphere from contact with the part of the wall of the dielectric not covered by the conductive liquid. A glass or ceramic container 10 has a recessed upper part holding a tubular ceramic dielectric 12 with an outer conductive electrode layer 13 sealed to the container at both ends 15. The container is filled with mercury 20 and paraffin 21 and has a cover 14 with a bushing 16 receiving a screwthreaded metal rod 17 carrying and projecting through a cylindrical insulating block 19 which is raised from or lowered into the mercury or glycerine on rotation of the rod, so as to displace the conductive liquid against the inner wall of the tube 12. The electrode layer 13, e.g. of silver or graphite, may be formed on the outer upper part of the container and covered with varnish. The electrode layer 13 may be formed on the inside of a dielectric tube sealed at both ends and secured to the rod 17 for regulated immersion in the mercury, the container being of metal or insulating material. In a construction similar to Fig. 1 a metal rod is sealed axially in a glass container under a vacuum or containing inert gas and the displacement body is a cylinder of ferro-magnetic material sliding on an axial metal rod 38 and moved by a permanent magnet or by an electromagnetic coil surrounding the container. In Fig. 5 a glass container 36 has an axial metal rod 38 on which slides a cylinder 42 of ferro-magnetic material surrounded by a dielectric tube 43 with a conductive electrode layer 44 on its inner surface, the cylinder being moved by an external coil 39. The container may be sealed and the control rod may be connected to the container by an expansible bellows. The conductive electrode layer may be shaped as desired or divided into two or more parts.