GB664418A - Improvements in or relating to glow discharge tubes and circuits therefor - Google Patents

Abstract

664,418. Discharge apparatus. PHILIPS ELECTRICAL, Ltd. Jan. 12, 1949 [Jan. 14, 1948], No. 853/49. Class 39 (i). In a glow discharge tube of the type described in Specification 644,369, in which the cathode consists of a metal with a melting point above 1400‹ C. and the envelope is coated over substantially the whole of its inside surface with a layer of the same metal, ignition is facilitated by providing at least one auxiliary electrode, between which auxiliary electrode and a main electrode or a second auxiliary electrode a current is caused to flow which lies in the Townsend region of the glow discharge characteristic curve. The discharge tube, Fig. 1, comprises a glass envelope 1 and a flat bottom 2 having four chrome-iron pins sealed therethrough. The cathode 4, consisting of a slightly V-shaped sheet of molybdenum, is supported by two of the pins 3. A molybdenum wire anode 5 placed at a distance of 0.5 to 0.8 mm. from the cathode is supported by the third pin, while the fourth pin 6 forms an auxiliary anode. The gas filling consists of neon and 1 per cent argon at a pressure of 30 mm. Fig. 2 shows the tube 11 connected in a circuit suitable for indicating when a flash of light attains a predetermined level of illumination. D.C. mains terminals 14, 15 are respectively connected to the cathode 12 of the tube and the anode 17 of a photo-electric cell 16 having a cathode 18. Upon exposure of the cell 16 to a flash of light of the requisite intensity the condenser 19 is charged to the voltage at which the tube breaks down and relay 20 operates to close contacts 21 which may be connected to an indicator or the like. The auxiliary anode 22 is connected to the positive terminal 15 through a resistance 23 of such magnitude that a constant current of 2.5 micro amps flows through it, even before ignition of the tube 11.