GB110057A - Improvements in and relating to Electrical Discharge Tubes. - Google Patents

Abstract

110,057. British Thomson-Houston Co., (General Electric Co.). Dec. 7, 1916. Relays.-A discharge tube capable of use in an electric surge indicator has electrodes at a short distance apart, say, “mm. to 1 mm., in a gas which is kept pure by a substance such as calcium, magnesium, or alloys thereof, reacting with nitrogen, oxygen, water vapour and hydrogen. One electrode, preferably the cathode 1, may be made of such a substance, the other electrode 2 being a rod of tungsten, or molybdenum; or both may be of the reactive substance. The anode should not be larger than the cathode, and is preferably smaller, as shown. Both are preferably pointed. A rare atmospheric gas such as argon or neon, at a pressure of 20-40 cm. of mercury, is a suitable filling. Initially, the gas is purified by repeatedly passing a high-pressure current. In the use of the tube, a high-pressure discharge of about a micro-ampere, caused for instance by excessive pressure in a main 7, renders the tube conductive for a low-pressure current from mains 12. This current may excite an electromagnet 15, which operates a recorder or indicator such as a bell 18 and temporarily breaks the low pressure circuit. Between the high.pressure main 7 and the tube are a spark-gap 8, an insulator 9 having capacity, and a smaller gap 10. An earthed condenser 11 protects the low-pressure circuit. Specification 7997/15, [Class 39 (i), Electric lamps, Arc &c.], is referred to.