Patent GB-782669-A (GB)
Title: Improvements in or relating to electrical circuits using multi-gap cold cathode gas-filled glow discharge tubes
Inventor: JACKSON THOMAS MEIRION
IPC: H03K29/00
Filed: 1953-11-25
Abstract: 782,669. Electronic counting apparatus. STANDARD TELEPHONES & CABLES, Ltd. Nov. 19, 1954 [Nov. 25, 1953; March 19, 1954], Nos. 32779/53 and 8108/54. Addition to 692,415. Class 106 (1). [Also in Group XL (a)] The phenomenon of " sticking " in a counting tube of the type described in the parent Specification in which some at least of the cathodes are directional, whereby the discharge steps from a storage cathode to a transfer cathode and then back to the same storage cathode, and which is believed to be due to a small leakage current flowing in the transfer gap ahead of a discharging storage gap, is overcome by circuit arrangements which either bias the transfer cathodes to a positive potential such that the flow of current from a transfer cathode in the absence of a stepping pulse is prevented, or bias the transfer cathode to a potential of the order of that of a discharging storage cathode such that a substantial current of the order of hundreds of micro-amps. but still considerably smaller than the normal discharge current flows in the transfer gap ahead of a discharging storage gap. In the latter case the current is believed to exercise a function analogous to cleaning the transfer cathode. The circuit shown in Fig. 1 utilizes the first of the above arrangements. The tube MCT has its storage cathodes each connected to earth via a resistorcapacitor circuit such as R1-C1, and its anode connected to a positive supply of 330 volts via a resistor R2. The voltage drop across a cathode resistor is about 50 volts. The commoned transfer cathodes are connected via a resistor R3 and a rectifier MR1 to a point on a potential divider formed by resistors R4 and R5 which are so chosen that the voltage at their junction, which is the voltage normally present on the transfer cathodes, is of the order of + 170 volts. Due to the presence of MR1, the transfer cathodes can go negative to, but not positive to + 170 volts. This action of MR1 is facilitated by connecting MR1 to positive via a large resistor R6, so that MR1 always passes current. The difference between the voltage of a discharging storage cathode and the transfer cathodes is thus about 120 volts, a transfer cathode being positive to a storage cathode, with the result that during the intervals between pulses flow of current in a transfer gap ahead of a discharging storage gap is substantially prevented. The capacitor C2 stabilizes the voltage at the-junction of R4 and R5. Stepping pulses of - 250 volts are supplied to the transfer cathodes via capacitor C3 and resistor R3. Control plates C which control the area of the cathode flow and screen the discharge gaps from external influences are connected via a current-limiting resistor R7 to a point on a bleeder formed by resistors R8 and R9. Fig. 3 shows a circuit utilizing the second of the above arrangements. The commoned transfer cathodes of the tube MCT are connected to earth via a resistor R4 and to a point on a bleeder formed by resistors R5 and R6 via rectifiers MR1 and MR2. The junction between rectifiers MR1 and MR2 is connected to the positive supply via a high resistor R8. The resistors R5 and R6 are so chosen that current normally flows through R8 and MR2, MR1 is biased to its high resistance condition and the transfer cathodes are virtually isolated from the rest of the circuit. In this condition a discharge of the order of 200-500 microamps. flows from the end of the transfer cathode ahead of the discharging storage cathode and passes through resistor R4 which is so chosen that the transfer cathodes are biased to within a few volts of the voltage of a discharging storage cathode. A negative pulse applied to the input terminal P passes to the transfer cathodes via C3 and MR1 and at the same time biases MR2 to its high resistance condition. The transfer cathode ahead of the discharging storage cathode then discharges fully. The. anode of the tube is connected to the positive supply through two resistors R2 and R3 in series. A capacitor C2, connected in parallel with R3 serves, as described in Specification 725,539, [Group XL (c)], to supply the increased current which is needed during the full discharge of a transfer gap. The control plates (or plate) are connected to earth via a self-biasing resistor R7, and the storage cathodes are each connected to earth via a resistorcapacitor circuit such as R1-C1. A modified form of the circuit shown in Fig. 3 is described in which the rectifier MR1 is replaced by a gas-filled discharge tube.