GB582932A - Improvements relating to spark gaps - Google Patents

Abstract

582,932. Spark-gaps. JONES, F. L. Feb. 17, 1941, No. 2093. Drawings to Specification. [Class 39 (i)] [Also in Group XXVII] A high-voltage spark-gap especially suitable for aircraft ignition systems comprises a gasfilled air-tight envelope in which the electrodes are sealed and rigidly supported and are so disposed that a uniform electric field is maintained over a substantial fraction of the sparkgap volume; the electrode material has a work function greater than 4.0 electron volts<1>; and the product of the pressure p and distance d apart of the electrodes is greater than five times the value of this product which corresponds to the minimum sparking potential of the gas. Very short breakdown times are obtained, ranging from 10-<4> to 10-<10> seconds. The preferred electrode materials are tungsten, molybdenum and platinum. The filling may be nitrogen or hydrogen; for aircraft the preferred filling is nitrogen at 50-100 cms., preferably 70 cms. Rare gases may also be used, with precautions against metastable states, but metallic vapours should be avoided. The electrodes in the preferred form illustrated are flat discs with rounded edges sealed into a hard-glass envelope by tungsten rod supports. The ratio of diameter to distance d should exceed 10, and d should be greater than 0.2 mm. and may be as great as 1.5 mm. Cooling is provided to reduce thermionic emission, which tends to prolong the spark, although a small degree of emission may be desirable to increase the reliability of breakdown. The whole envelope may be immersed in an oil-bath. The gap may be used for radio circuits.