Patent GB-525902-A (GB)
Title: Improvements in or relating to electrical signalling systems particularly for line or apparatus identification purposes
IPC: H04M15/08
Filed: 1939-03-02
Abstract: 525,902. Electric selective signalling. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. March 2, 1939, Nos. 6905 and 7462. [Class 40 (i)] [Also in Group XXXIX] To enable lines in a calling or other condition to be identified at another stage of the connections in which they are involved, a rotary switch or its equivalent applies potential momentarily one or more times to the test wire of each line in the course of a cycle, so that characteristic impulses are transmitted over the various connections then existing to operate storage apparatus under the control of switches rotating in synchronism with the sending switch. A single large-capacity switch may be employed instead of individual switches, some wipers being used for sending and some for receiving. The invention is particularly useful in connection with the automatic ticketing of toll calls. In the simplest application to a 10-line exchange, Fig. 8, the sending switch SS connects A.C. to the test wires in succession, so that a relay PUR associated with an outgoing relay group ORS energizes when the calling line is encountered and connects up a corresponding relay USR7 over the receiving switch RS. An extension of this arrangement for a 100-line exchange employs impulses of different frequency for the tens and units digits, which are independently sent over separate wipers. An alternative arrangement, Fig. 4, relies entirely on the spacing of the impulses. The switch SS has 8 banks of 25 terminals and is capable of applying two impulses for each of 100 lines, each digit being represented by a two-letter code. The two banks of the switch RS are wired to tens and units relays corresponding to the code letters V-Z as shown. Thus the line 11 is represented by VW. VW and storage relays corresponding to those letters are operated. In a larger exchange, one switch SS is provided per 100 lines, and further switches may be provided for determining the thousands and hundreds digits, the two stages of identification taking place in succession. In a telephone area employing a linked numbering scheme, the outgoing relay group ORS at a satellite exchange receives the variable part of the calling number, e.g., the last two digits, during the setting up of the call, and at a later stage transfers the complete number to the main exchange. The circuits are shown in Figs. 5, 6, 7 in which the receiving switch RIS has wipers individual to each relay group and may if desired carry wipers to provide the sending switch. Upon seizure, relay SI starts the switch RIS, or, if it is already in motion, operates RI to ensure that it will perform another complete cycle. When SI falls back at the end of the call, a switch TS is started to transfer the calling number, the connection being held meanwhile by the operation of G. The digits are represented by the two-letter code referred to above, and the terminals of TS are selectively grounded as indicated in Fig. 6, the connections for the first three digits being invariable and those for the remainder being dependent on the storage relays. At each step of TS, relay P sends an impulse over the junction to step the receiving switch RS at the main exchange. On each grounded terminal, however, relay R pulls up and reverses the impulse current to operate relay B instead of A in order to produce a storage effect. The transfer may alternatively be initiated by the reply of the called party.