Patent GB-692415-A (GB)
Title: Improvements in or relating to electric discharge tubes
Inventor: HOUGH GEORGE HUBERT
IPC: H01J17/48
Filed: 1948-09-30
Abstract: 692,415. Discharge apparatus. STANDARD TELEPHONES & CABLES, Ltd. Sept. 23, 1949 [Sept. 30, 1948], No. 25487/48. Class 39(i) [Also in Group XIX] In a cold cathode gas-filled electric glow discharge tube comprising electrodes defining an ordered array of discharge gaps arranged to fire in sequence with the discharge at one gap of the array priming the next successive gap by ionization and field coupling, certain of the said electrodes are asymmetrically shaped with respect to adjacent gaps in order to concentrate discharge there-at in the neighbourhood of the next succeeding gap so that the discharge may be transferred from gap to gap along the said array in one direction rather than the other. One form of electrode construction is shown in Fig. 3, in which a number of metallic strips clamped between two sheets 60 and 61 of mica or other suitable insulating material are bent over to form cathodes facing a common anode 51. Cathodes 52 and 53 are storage cathodes while cathodes 54 and 55 are transfer electrodes. Each storage cathode, 52 for example, comprises a tail portion 56 and a plate portion 57. The tail has a smaller discharge surface area than the plate, but has a considerably larger ratio of periphery to surface area; furthermore it is further away from the anode than is the plate. In consequence the tail portion passes into abnormal glow at a lower current than the plate portion, but requires a higher maintaining voltage. The discharge surface of the plate portion is separated from the discharge surface of the tail portion by a small vertical step; consequently when a storage cathode is primed by a discharge at the adjacent transfer electrode, cathode glow starts on the end of the tail adjacent to the transfer electrode and spreads over the whole tail surface. When the cathode glow reaches the step. the striking voltage of the plate portion is reduced owing to the coupling between the tail and plate gaps and the plate portion is fired by the anode battery potential. Since the maintaining potential of the plate portion is lower than that of the tail portion, it is possible to limit the total discharge current through the gap to a value such that the gap voltage is lower than the maintaining voltage of the tail portion. The discharge on the tail portion is therefore extinguished and coupling to the following transfer gap 49 is much greater than to the preceding transfer gap 47. The backward coupling may be still further reduced by bending alternate pairs of cathodes in the opposite direction. In a circular array construction, Fig. 6 and 7, the transfer electrodes 72, formed by the bent over fingers of a metallic spider 76, a separate transfer electrode 77, and separate storage cathodes 71, located between adjacent transfer electrodes, are all sandwiched between a circular insulating plate 73 and a pair of annular insulating plates 74 and 75. The cathode assembly is sandwiched between a pair of annular metallic discs 78 and 79 having upturned rims directed away from one another, these discs functioning as field control plates to confine the cathode glow to the desired surfaces of the cathodes. The anode 80 is located by mica discs 85 and 86 and is supported by two rods 89 welded to eyelets 87 and 84 in the anode and cathode assemblies respectively. The complete structure is mounted on support rods 90 and 91, rod 90 serving as a lead to the field control plates. Leads 93 are welded to the storage cathodes and transfer electrodes and are taken to the pinch, while anode lead 94 is taken to a top cap on the tube envelope. In another form of construction of a radial type of tube, Fig. 10, the bending over of electrodes is avoided. The storage cathodes are formed with a stepped edge to provide a cathode plate 107 projecting beyond the tail 105. The transfer electrodes are shaped similarly to the cathode plates, and are not bent over. The control plates 108 and 109 are circular, without serrations and the anode 110 is substantially flat. Discharge at the cathode tail can occur only along its outer edge while discharge at the cathode plate is limited to its upper surface. In a circuit arrangement for the above tubes, Fig. 2, the storage cathodes are arranged in two groups 29 and 30 connected to resistance-capacity circuits 34 and 35 respectively, one separate storage cathode 31 being connected to an individual resistance-capacity circuit 36 containing a pulse output transformer 37. The transfer electrodes 32 are connected through resistance 38 to a biasing battery 39 and through blocking condenser 42 to a pulse input terminal 43. The separate transfer electrode 33 is connected to a switch 40 enabling it to be connected either in the same way as the other transfer electrodes, or through resistance 44 to a battery 45. The anode 28 is connected through resistance 47 to a battery 46. The anode and cathode resistances, together with the potential of battery 46 are so proportioned that a discharge may be maintained at any one storage gap once that gap has fired, but the potential fall across the common anode load is sufficient to extinguish discharge at the storage gap when a transfer gap is fired. The bias applied to the transfer electrodes is such as to ensure that the anode battery shall not maintain a discharge at any of them. Assume now that a discharge is existing at one of the storage gaps. If a negative pulse is applied to terminal 43, discharge will occur at the adjacent transfer electrode which has been primed by the discharge at the storage gap, the pulse amplitude being made insufficient to cause discharge at any of the other transfer electrodes, which are all unprimed. When the transfer electrode fires, the storage gap is extinguished, the pulse supplying sufficient voltage to maintain the discharge at the transfer electrode. The cathode potential of the gap which has just been extinguished is maintained positive due to the charge storing circuit to which the cathode is connected, but the cathode potential of the storage gap on the other side of the transfer electrode now disdischarging is at or near earth potential, as its resistance-capacity circuit is as yet uncharged. When the pulse has passed, current ceases to flow in the anode circuit so that the full battery potential appears across this next storage gap, which, under the influence of the ionization and field coupling from the transfer gap which has just gone out, now starts to discharge. The cathode charges up exponentially, so for a time the anode current is greater than normal, thus preventing any other storage gap from firing; at the same time the cathode potential of the previously discharging storage gap continues to decay exponentially. A further pulse applied to terminal 43 will cause the discharge to transfer to the next storage electrode in the direction indicated by the arrows. A "homing" facility is provided by the key 40 which on operation causes discharge of transfer electrode 33 thus extinguishing discharge at any of the storage cathodes. When the key is released, either the adjacent cathode 29 or cathode 31 is fired, depending on the state of charge of the condensers in the respective circuits 34 and 36. If necessary, a second operation of the key suffices to transfer the discharge to that one of cathodes 29 or 31 it is desired to regard as the first storage cathode in the sequence. In a modified construction, the transfer electrodes are shaped as triangles to also provide some degree of directional coupling, while the lower control plate, corresponding to member 79 of Fig. 7 is slotted, having bent over castellations lying behind the transfer cathodes and the plate portions of the storage cathodes, the portions between the castellations being cut away to leave projections parallel to the cathode tails. The member 78, formerly the upper control plate, now serves merely as an anode locating cup, a further member in the form of a metallic disc sandwiched between the locating cup and mica disc 73 now functioning as the upper control plate. In a further development, all the cathodes are constructed on the unidirectional principle and the separate transfer electrodes are omitted. The cathodes are arranged in two groups, each connected to ground through a resistancecapacity network. Negative extinguishing pulses to be counted are applied to a common anode. The counting speed may be increased if the resistance-capacity circuits are omitted, and this may be done if the transfer electrodes are reintroduced. but are shaped similarly to the storage cathodes, so that all cathodes provide unidirectional coupling. In Fig. 13. cathodes 125 are mounted on either side of a sheet 124 of mica or other insulating material, the cathodes at the ends protruding beyond the edge of the mica sheet to give the equivalent of a circular array. Control plates 127 are mounted on the mica sheet below the cathodes and two anodes (not shown) connected together are mounted above. The transfer electrodes 128, Fig. 15, are biased positively by a battery 129 so that they will only maintain a discharge in the presence of a negative pulse applied to terminal 130. The remaining cathodes, the storage cathodes, are connected through a resistance 131 to ground, with the exception of storage cathode 132 which is connected to ground through an output transformer 133. The pulses must be sufficiently long for the residual ionization to decay in the gap which is extinguished by firing of the transfer gap. Specifications 639,827, 644,926 and 691,901 are referred to.