Patent GB-656214-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04M15/08
Filed: 1949-08-16
Abstract: 656,214. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., SMART, N. C., CHUBB, A. A., and MAWSON, R. Aug. 16, 1949, No. 27087/48. [Class 40 (iv)] In a calling line identification system of the type in which a signal is applied to a wire characteristic of the caller and finder-means hunt for the marked line, the signal is inaudible, a plurality of switches hunt simultaneously for a contact carrying the signal, the successful switch is stopped and a further switch determines which wiper of the stopped switch is associated with the signal. On a demand for identification from the operator's position 5 (Fig. 1), the switch 6 connects the position to the common apparatus group 7 which emits a signal, of, say, 10 kc. frequency which is reverted over the switch train preferably on the P wire, and starts all the identification finders such as 8. Each of these finders has access to 100 subscribers and its wipers are connected together through small capacitors. When the wipers of a finder such as 8 pick up the signal, operation of a detector in the associated identification group 9 stops the switch and disconnects the wipers from each other. A further switch (not shown in Fig. 1) then hunts for the wiper of the first switch carrying the signal to complete the identification. Detailed operation (Figs. 2, 3). A subscriber making a trunk call dials TRU and is routed to an operator's position in the normal way. The operator initiates identification, a 10 kc. signal being applied to the subscriber's P wire and ground being applied to a common start wire operating all the ST relays (Fig. 2) of the identification groups. Considering one such group, the operation of ST starts the switch U which has five contact banks (U1 to U5, Fig. 3), each having 20 contacts wired to the P wires of subscribers' lines. The five wipers associated with these banks are connected to a detector X. When a wiper reaches the marked contact, say contact 8 of bank U2, detector X operates relay D which stops switch U. Relay H locks up, disconnects X, whereupon D releases, and connects bank T1 of the second switch T to X. Relay CO (Fig. 2) pulls up, disconnects wipers U1 to U5 from each other and connects them to contacts of bank T1, and starts switch T hunting for the wiper of U carrying the signal. Detector X operates to the marked contact of T1 and brings up D which stops T. The consequent operation of TS releases H which disconnects the wipers of T and U from the detector X and energizes IM. IM operates and releases at a rate of about 10 per second and impulses switch DS. Two separate V.F. frequencies A and B and a combination of the two are derived from the common apparatus group 7 (Fig. 1) and are applied to banks U6, U7, T2, T3 and T4. Wiper DS1 encounters no frequency for its first four steps during which period the 10 kc. signal is removed from the P wire by the common apparatus group. In positions 6 and 7 DS1 picks up A, B or A+ B depending upon the contacts upon which U6 and U7 are standing. These two signals which characterise the units digit of the calling line are applied over a front contact of IM to the P-wire and thence over the switch train to the common apparatus group where they are registered. On the next two steps DS1 picks up further signals over banks U8 and T3 or T4 and T2 respectively indicative of the tens digit, and on contacts 10 to 13 signals over the cross-connecting frame F individual to the switch U are picked up characteristic of the hundreds and thousands digits. The registering equipment then causes a lamp display to appear on the operator's position showing the caller's number. When DS steps to contact 14 ST is released followed by TS and IM. Switch DS homes over bank DS3 and the switches of all the other identification groups cease stepping. If the operator is at an exchange other than that of the caller the V.F. code applied to the P wire may be transformed to the speech wires and transmitted over the junction, as may the start signal also.