Patent GB-735138-A (GB)
Title: Improvements relating to fault signalling in telephone systems
Inventor: SMITH SYDNEY FRANCIS
IPC: H04Q1/26
Filed: 1953-03-13
Abstract: 735,138. Exchange systems. SIEMENS BROS. & CO., Ltd. March 5, 1954 [March 13, 1953], No. 7060/53. Class 40 (4). An unattended exchange is connected to an attended exchange over a plurality of junctions normally connected to provide a conversational path between the two exchanges, and on the occurrence of a fault at the unattended exchange a free one of the plurality of junctions is disconnected from the conversational path and connected to an alarm signalling circuit and a distinctive signal is transmitted over the junction to bring about at the attended exchange the disconnection of the junction from the conversational path and the giving, of an alarm signal. Figs. 1 and 2 show equipment at an unattended and an attended exchange respectively, suitable for alarm signalling over either of two bothway junctions, and Fig. 3 is a modification of Fig. 1 showing equipment suitable for alarm signalling over any one of a number of junctions greater than two. Alarm signalling over either of two junctions, Figs. 1 and 2. At the unattended exchange, Fig. 1, relays AE and AF are normally held operated to maintain a through telephone circuit over junctions J1 and J2, of which J1 is the first choice for alarm signalling. The closure of alarm contact a applies a short-circuit to the energized left-hand windings of relays AE and AF. If the first-choice junction J1 is free, relay AE releases and completes a holding circuit for AF (which is slow-releasing). The release of AE disconnects junction J1 from the usual both-way relay set (not shown) and loops the junction wires to the relay set where the guard relay operates to close its contact b. Earth is extended over the negative wire of junction J1 to operate a differential relay E at the attended exchange, Fig. 2, which busies the junction, gives an audible alarm if required, and lights an alarm lamp LP2 at a test desk. The attendant operates a key KRA to bring up a relay AD which connects battery over the lower winding of relay E (which releases) and the positive wire of junction J1 to the unattended exchange, where relay RS is energized, followed by relays RA and AE. Relay RS then releases. At the attended exchange the relapse of relay E causes the operation of relays AC and AZ and the release of relay AD. A lamp LP1 is now lit in place of LP2, and the key KRA may be released. The junction J1 is now free for normal operation, and the alarm circuits are locked in the " receiving attention " condition with relays RA, AC, and AZ operated. When the faults have been corrected, the alarm contact a is opened. If, at the time of the closure of the alarm contact a, junction J1 had been busy but J2 had been free, relay AE would have been held by the closed contact b so that AF would have released and the alarm signal would have been transmitted over junction J2, relay F functioning in place of E at the attended exchange. Following the clearance of the faults and the opening of alarm contact a, when a junction becomes free the corresponding relay AE or AF releases and operates relay E or F as before, so that relay AC releases and initiates the slow release of relay AZ. During the release period of AZ battery is connected over the positive wire of the junction to operate relay RS at the unattended exchange. This causes the release of relay RA and the re-operation of relay AE or AF, and the final release of AZ, followed by RS, and of E or F completes the restoration of the equipment to normal. In a modification (not shown), the release of relays AE and AF is arranged to connect earth directly to the junction test wires without the intervention of the guard relay. Alarm signalling over any one of more than two junctions, Fig. 3. At the unattended exchange each junction has an associated " selecting relay," such as AE, and a " position relay," such as AP. The left- and right-hand windings of the " selecting relays " are connected in a similar manner to those of the relays AE and AF shown in Fig. 1, relays RA and RS correspond to those shown in Fig. 1, and the " position relays " are connected to the junction test wires similarly to the middle windings of relays AE and AF in Fig. 1. When a junction is free, the associated guard relay contact band " position relay " are unoperated and the " selecting relay " is operated; the unoperated "position relay" maintains holding circuits for the middle windings of later-choice " selecting relays." The seizure of a junction closes contact b to bring up the " position relay which holds the associated " selecting relay operated over its middle winding and breaks the circuit for the middle winding of the nextchoice " selecting relay." An alarm is initiated by the short-circuiting of the left-hand windings of the " selecting relays," as described above in connection with Fig. 1. The relay associated with the earliest-choice free junction is released, the other " selecting relays " being held over their middle windings. For example, if the first-choice junction J1 is free, relay AE releases and initiates alarm signalling which proceeds as described above. The release of relay AE also completes a holding circuit for the other " selecting relays " and disconnects a direct earth and earth over relay RS which would otherwise cause an alarm over all the junctions in the event of a complete battery failure. In a modification, Fig. 4 (not shown), the position relays " are dispensed with and their contacts are replaced by change-over contacts of the junction guard relays.