GB776254A - Improvements in t.r. cells - Google Patents

Abstract

776,254. T.-R. switches. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 16, 1954 [Jan. 8, 1954], No. 615/54. Class 39(1). In a T.R. cell, as described in Specification 698,896, in which one of the main electrodes has associated therewith an auxiliary priming electrode in the form of a conductor substantially completely shielded by said main electrode from the other main electrode and from said main electrode by a surrounding sleeve of vitreous material which exposes the tip of the auxiliary electrode, the auxiliary electrode incorporates a resistor which is in series with and is close to the tip thereof and serves to stabilize the priming discharge. The auxiliary electrode shown comprises a metal or alloy conductor 24, a ceramic resistor 25 and a nickel extension wire 26 to which is welded a rhodium tip 27. The conductor 24 is surrounded by a glass sheath 31 to which is seated a ceramic insulating sleeve 30 surrounding the resistor 25 and extension wire 26. A glass bead 32 is provided to locate the auxiliary electrode within the main electrode. The resistor 25 is provided with sleeves 29 which are welded to the conductor 24 and extension wire 26, or alternatively the end caps of the resistor may be welded directly thereto. In a further alternative construction the end of the extension wire 26 is coiled around one end of the resistor 25, and a short length of wire is coiled around the other end and welded to the conductor 24, the contacting portions of the wires and resistor being metallized. The glass sheath 31 may be extended to replace the ceramic sleeve 30 and may be heated where it surrounds the resistor 25 to collapse the glass on to the surface of the resistor. A resistive oxide layer may be used in place of the ceramic resistor, and in an alternative design a wire of iron-nickel cobalt alloy is sheathed with glass, the end exposed by grinding, oxidized by heating in air, and then copper plated. The copper which forms the electrode tip, is preferably oxidized on its surface to protect the resistive oxide layer from electrochemical attack by the water vapour in the fitting, which consists of argon with a trace of water vapour.