Patent GB-253646-A (GB)
Title: Improvements in automatic and semi-automatic telephone systems
IPC: H04Q1/32
Filed: 1925-04-02
Abstract: 253,646. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd.), and Baker, J. H. E. April 2, 1925. Automatic exchange systems.-Fault alarm signals are extended from one exchange to another over an inter-exchange junction normally used for conversation, without interfering with the normal traffic thereover. If the junction is busy, the transmission of the alarm signal is held up until it becomes free. The alarm is then sent and the junction held busy until the fault is cleared. When a fault signal is received at the main exchange, a particular " alarm " lamp lights and a bell is rung. A key is then thrown to disconnect the " alarm " lamp and bell and light an " attention " lamp. Means are provided at the main exchange for transferring the alarm signal from one position to another. In the system shown, an alarm at a sub-exchange (on the left of the drawing) is extended over a two-wire junction WE, WF extending to the line relay A of an incoming group selector at the main exchange. An automatic room attendant's position is shown in the centre portion of the drawing and a manual room attendant's position at the right of the drawing, keys KB, KC being provided at both positions, whereby alarms at the automatic position may be transferred to the manual position from either position. If ground is placed on an urgent alarm bus-bar BB at the sub-exchange and the extension key KA is not depressed, a 2500- ohm. trembler bell at the sub-exchange is rung over lead WC. If, however, the key KA is depressed, a circuit is closed for an alarm relay Z associated with the inter-exchange junction WE, WF. Should the junction be busy, the relay Z is shortcircuited over the private wire WG, but if the junction is idle (or when it falls idle), the relav Z pulls up, grounds the private wire WG and the positive line WE, thereby energizing the righthand windings of a relay U and of the line relay A. Relay A energizes the release relay B, which closes a locking circuit for relay U over its halfstep contacts 6, 5 and grounds the incoming selector private wire P, thus closing a circuit over the outer right-hand armature of a relay V, outer lefthand armature of relay U, keys KB. KC (assuming they are not thrown), and lead WK, for an urgent alarm lamp LE and an alarm relay PA: relay PA closes a circuit for a 2500-ohm. trembler bell. The attendant then throws a key KF, energizing a relay X, which de-energizes relay A, locks to the grounded line WE, grounds the private wire P, de-energizes the alarm lamp LE and relay PA, and lights an " attention " lamp LF. When the fault is cleared, relay Z relapses, the junction is freed, and the circuits of the relays U, X, and lamp LF opened. Non-urgent alarms over the bush-bar BA are extended in a similar manner over another junction, 1000-ohm. A.C. ringers being associated with such alarms. When the junction WE, WF is used in an ordinary call, one of the windings of relays U, V are energized over the loop, these relays locking up over their other windings when the private wire P is earthed, to close a direct path for speech currents over their contacts. The alarms may be extended at night to the manual attendant's position from the automatic attendant's position by throwing key KB. Alternatively the manual attendant can ascertain whether the key KB has been thrown by operating a key KK and noting whether the lamp LJ lights. If it does not, he throws his key KC which duplicates the operation of key KB. In either case the lead WJ is extended to the lead WL so that when the private wire P is grounded by the relay B, the alarm lamp LG and relay PB are energized at the manual position. When the key KG is thrown, a relay Y energizes instead of relay X and performs similar functions, including lighting an " attention " lamp LH. Alarms originating at the main exchange are dealt with in the following manner. During the day, if ground is placed on a bus-bar BC (provided for day and non-urgent night alarms) or on a bus-bar BE (provided for day alarms only), a 1000-ohm. A.C. ringer at the automatic position is operated, whereas if ground is placed on a bus-bar BD (provided for day and urgent night alarms), a 2500-ohm. trembler is rung. At night, when either of the keys KB or KC is thrown, the day only alarm circuit over the bus-bar BE is broken, but the bus-bars BC, BD are extended to the manual position. If then the bus-bar BC is grounded, an alarm lamp LC and relay PC are energized and a 1000-ohm. A.C. ringer is operated, and when the key KE is thrown, these are disconnected and an " attention " lamp LD lighted. The bus-bar BD is extended in similar manner, an alarm lamp LA. relay PB, key ED and " attention " lamp LB being used in this alarm. Keys KH, KJ are provided for testing the alarm lamp and relay circuits.