Patent GB-669822-A (GB)
Title: Dialling system for automatic telephony
IPC: H04Q1/40
Filed: 1948-04-02
Abstract: 669,822. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. April 2, 1948 [April 8, 1947], No. 9311/48. Class 40 (iv). [Also in Group XXXVIII] Numerical digits distinguished by the time interval between two successive impulses control the operation of gas tubes located at an exchange, the time interval being measured by applying the impulses to the gas tubes both over a delay line and directly so that the tube controlled by the appropriate digit is fired by the simultaneous reception of two successive impulses. Circuits may also be provided for discriminating between two or three separate digits using the same time interval but characterized by different polarities. As shown in Fig. 2, the operation of a subscriber's impulse contact 21 completes a circuit for a battery 15 and induces corresponding impulses in the secondary winding of a line transformer 22, each contact making successive time-spaced closures for the two impulses. The impulses are applied to a delay line 25 and to the anodes 27 of gas tubes '26. The first impulse applies positive potential to the control grid 29 of the tube appropriate to the contact operated at the same time as the anode is made positive by the second impulse. The tube ionizes and operates an associated relay 30 which controls the operation of a register and de-ionizes the tube. In a modification the battery is connected across the line with resistance in series, the operation of contacts 21 short circuiting the transformer primary winding. In a second embodiment, Fig. 6 (not shown), a single D.C. impulse is applied to the transformer primary winding by closing a contact 21 for a particular time interval. Two impulses of opposite polarity and spaced apart by the time of operation of contact 21 are thus generated in the secondary winding and effect the operation of the gas tube associated with the operated contact. In a further embodiment, Fig. 8 (not shown), the delay line and the gas tube anodes are connected to separate transformer secondary windings. Rectifiers may be included in the circuit of each secondary winding to eliminate the first impulse from the anode circuit and the second impulse from the delay line. In these embodiments individual delay lines may be provided for each tube, or be common to only a few of the tubes. Some sections of the delay line may also be used twice by incorrectly terminating the line so that some tubes are operated by the reflected impulse. Two different digits may also be characterized by the same time interval but differentiated by the polarity of the impulse. As shown in Fig. 10, polarized relays 50, 51 discriminate the polarity of impulses which are obtained by the rectification at rectifiers 44, 45 of an A.C. supply from a generator 46 when either contact 42 or 43 is operated. In a modification one of the discriminating relays 50, 51 may be initially operated by a single impulse, the register relays being subsequently controlled by transmitting pairs of A.C. impulses. In a further embodiment, Fig. 11 (not shown), discrimination is provided between three different digits characterized by the same time interval, two polarized relays being operated together by A.C. impulses when a third key which is not provided with a rectifier in series is used. A dialling device (not shown) for use with the invention comprises a double sector member, each sector being provided with finger holes corresponding to five digits.