Patent GB-609474-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q1/444
Filed: 1940-06-11
Abstract: 609,474. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and WRIGHT, E. P. G. (Hertog, M.den (in part).). June 11, 1940, No. 10163. [Class 40 (iv)] In a system in which connections are set up over a number of exchanges arranged in a chain and in which A.C. of voice frequency is employed for impulsing and supervision, a backward signal is transmitted from each exchange in the chain to cause the registercontroller' at the originating exchange to resume sending and when all the numerical digits have been received at the final exchange a backward signal is sent to bring about switch-through at the originating exchange. The junctions are provided with repeaters at each end for sending and receiving the A.C. signals and the incoming repeaters are arranged to distinguish the " end of selection " signal from the " proceed to dial " signals. In the layout shown in Fig. 1, the first routing digit sent by the register-controller RG1 at exchange X effects selection of a junction TL1 to exchange Y. The incoming repeater TC2 in accordance with the second routing digit either brings about the association of a register-controller RG2 at that exchange which then receives the numerical digits or causes the seizure of a junction TL2 to exchange Z where the incoming repeater TC4 routes the call in a similar way. The " proceed to dial signal over the junction TL1 consists of an impulse of a single frequency, e.g. 750 cycles, and the " end of selection " signal consists of an impulse of the same frequency followed by two frequencies, e.g. 600 and 750 cycles, simultaneously. The signals received from ahead by the incoming repeater TC2 may be of the same character in the two cases, viz. a single break impulse, and the " end of selection " signal is recognized by the fact that two or more digits have been repeated forward without an intervening backward signal, while in another arrangement the " end of selection '' signal consists of two break impulses in rapid succession. The junction TL2 uses a different type of signalling from TL1, e.g. 50 cycles, and TC4 does not discriminate between " end of selection " and " proceed to dial signals as does TC2. The circuits for the first arrangement are shown in Figs. 2, 2a. Relay A, which is preferably controlled by a thermionic valve, responds to an A.C. impulse over the junction upon seizure and connects up release relay B which closes the forward loop through relay G. The latter energizes and connects up relays D, E. Incoming impulses are repeated by A, which holds G over a second winding, and dialling relay C is operative during each digit. Relay H is connected up by C, and remains locked at the end of the digit under the control of D. A " proceed to dial " signal comprising a single impulse is repeated back over the junction by G, D as an impulse of 750-cycle current, and H is unlocked. When however two successive digits are repeated forward without an intervening backward signal, relay J energizes at the first impulse of the second of these digits and opens the circuit over which D re-operates after it is disconnected by G. For. the "end of selection" signal, therefore, 600-cycle current is added to the 750-cycle current when H falls back, and re-operation of D follows the relapse of J. For the alternative arrangement, Fig. 2b, is substituted for Fig. 2a. A single impulse is repeated back by G, D as before, but relay C is operative to make a momentary circuit for H when G pulls up again. If a second impulse follows immediately, J energizes to give the characteristic " end of selection signal, C, H being held until J relapses. Specification 336,627, [Class 40 (iv)], is referred to.