Patent GB-655573-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1947-12-23
Abstract: 655,573. Automatic exchange systems. VIGREN, S. D., CLAESSON, P. H. E., and FREESE, H. Dec. 23, 1947, No. 34029. Convention date, April 4, 1945. [Class 40 (iv)] In a system of the type disclosed in Specification 152,702, [Class 40 (iv)], in which digits are signalled from a subscriber's substation to an exchange by momentarily connecting impedances in the line circuit, and an adjustable impedance at the exchange is automatically operated during each call to bring the line loop impedance to a predetermined value, an electronic impulse receiving device (e.g. a cathode-ray tube whose beam is deflected in accordance with the impedance inserted in the loop) in the exchange indicates the value of the current in the line loop and hence the digit signalled. Register, Fig. 1. When a call is made, a register associated with an idle trunk 41 is connected non-numerically to the calling line and relay R20 operates, connecting an individual ungrounded reversed battery E1 across the line. Relay R1 energizes, followed by R2, and a switch VM steps under the control of R3 to add resistance to the line until the beam of the cathode-ray tube is deflected to the left-hand electrode, when R4 responds in series with R19. It will be seen that the deflecting voltage is derived from the battery E1 and depends on the line resistance, which is made independent of the microphone resistance by the provision of series and shunt rectifiers L1, L2. Relays R5, R7 energize, and further resistances rp1, 2 are inserted in the line to swing the beam to the right-hand electrode, whereupon R8 responds and connects up R9 which disconnects R7 and the beam returns to the left. Relay R4 re-operates and connects up R11 which applies dialling tone. The subscriber actuates push buttons in accordance with the wanted number, thus inserting corresponding resistances in the line in turn. The beam of the cathode-ray tube is thus deflected to operate one of a set of twoposition relays R12-16 and the two digits are transferred to storage relays not shown, R17 being operated on the return of the beam after its deflection by the first digit. If R8 fails to energize when the beam is swung to the right, the slow release of R6, which was connected up by R5, operates R10 to give an alarm signal. Control of selectors, Fig. 2. For the tens digit, consecutive odd and even values are paired, and one of five wires t1, t2 ... is marked, together with t6 if the digit is even. The units marking is applied to one of ten wires e0, e1 ... Assuming the wanted number is 41, relay S<SP>2</SP>1a, corresponding to the second group of 20, energizes over t2, followed by S10, S50. Relays S<SP>1</SP>6, S<SP>2</SP>6 ... test over wires c1 to determine the trunk 41 (Fig. 1) associated with the calling line, and one of them energizes and connects up the corresponding selecting magnet SV1, SV2 ... of the switch MV. Relays S52, S21 energize and the selecting magnet SA1 of the switch AV operates over the marked units wire e1, followed by S13. Relays S<SP>1</SP>5, S<SP>2</SP>5... now test under control of S<SP>1</SP>1a for an idle link, and S<SP>1</SP>5, for example, connects up the holding magnet BV1, whereupon switching relay S20 operates over t6 and the holding magnet BA1 energizes to complete the connection to the wanted line. The application of battery to wire S by relay S13 brings about delayed release of the register, and the relapse of R20, Fig. 1, completes the connection to the calling line.