Patent GB-665820-A (GB)
Title: Improvements in or relating to electric counting circuits
Inventor: REEVES ALEC HARLEY
IPC: H03K29/00
Filed: 1947-06-05
Abstract: 665,820. Discharge apparatus. STANDARD TELEPHONES & CABLES. Ltd. June 4. 1948 [June 5, 1947], No. 14874/47. Class 39 (i). [Also in Groups XL (b) and XL (c)] A counting circuit equivalent in performance to the arrangement described in Specification 665,817, [Group XIX], which utilized a plurality of separate cold cathode gas-filled sequence electric discharge tubes, comprises successively operating arrays of discharge gaps in one envelope. The tube 1 has two flat, semi-circular anodes 2 and-3 and cathodes 4 and 5 of strips or wires of arcuate form from which points project towards the anodes. The gap lengths and gap spacing are all -about 2 mm. except gap 7 which may be shorter than the others. Separate cathodes 8 and 9 are arranged 3 mm. from the end cathodes 10 and 7 of arrays 4 and 5. Positive input pulses to be counted are applied at terminal 29 and thence to both anodes 2 and 3 via condensers 31 and 30 and rectifiers 33 and 32 which are shunted by high resistors 35 and 34 for de-coupling between anodes, the rectifiers ensuring that only positive pulses reach the anodes. Battery 13 is sufficient to maintain a discharge in any gap, but is insufficient to start a discharge. The pulse amplitude is arranged to be such that only the starting gap 7 on cathode 5 is fired when a first pulse is applied at terminal 29. The second pulse fires gap 6, owing to the spread of ionization from gap 7, but does not fire gap 9 as the spacing between 9 and 7 is greater than that between 7 and 6. Successive pulses will fire adjacent gaps on cathode 5 until all these gaps are discharging. The voltage between cathode 5 and anode 3 which, due to the presence of anode load resistor 11 and cathode load resistor 15, tends to vary with the number of gaps discharging. is stabilized by means of pulse choke 23 in series with battery 24 and rectifier 25, the rectifier being biased by the battery so as to be just non-conducting when all the points on cathode 5 are discharging. The next pulse fires cathode 8, and resistor 17 and condenser 21 are of such values that when this occurs a high current flows through gap 8 which gives rise to a voltage drop across anode resistor 11 sufficient to extinguish the discharges at all gaps. The large current in gap 8, however, produces sufficient ionization to prime gap 10 on cathode 4, which fires on the next pulse. Cathode 8 is unable to re-fire on this pulse because condenser 21, normally charged to the potential of battery 13, and discharged through 8 when it fires, will not have charged again to a sufficient degree. The discharges proceed along cathode 4 until the separate cathode 9 fires, whereupon all discharges to anode 2 are extinguished, and an output pulse is obtained at terminals 20. The next pulse fires cathode 7, which is primed by ionization from the large current flowing in gap 9, and the cycle is repeated. The first pulse applied at the commencement of operation of the tube must be of a higher amplitude than the normal pulse amplitude, in order that cathode 7 can fire in the absence of ionization. This can be arranged, for example, by applying the pulses to terminal 29 through a condenser bridged by a rectifier biased to cut-off by a voltage equal to the potential reduction required to ensure that the subsequent pulses cannot fire gap 7 unless it is primed by the discharge in gap 9. The arrangement may be used as a distributer, the points of cathodes 4 and 5 being led separately out of the tube and connected to individual external circuits. Three, four or more arrays of discharge gaps may be arranged in a single envelope and the arrangement may be poly. gonal instead of circular, or straight arrays may be arranged in zig-zag fashion. The gas filling may be as described in Specification 639,827, namely 92 per cent neon, 7 per cent hydrogen and 1 per cent argon at a total pressure of 100 mm. of mercury.