Patent GB-290396-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1927-03-09
Abstract: 290,396. Siemens Bros. & Co., Ltd., and Patterson, W. G. March 9, 1927. Automatic exchange systems.- Application of ringing current to one speaking lead when a call is switched through is temporarily delayed to allow a control relay to operate over the other lead to prevent the ringing current having an undesired effect. Circuits are described in which on a call to a dead, or out-of-order line, the control relay operates to trip ringing immediately it is connected, and then to connect up out-of-order tone. In the case of a normal call, the relay, operated during stepping of the connector is held energized to disconnect the ringing generator until the called line cut-off relay operates. In the case of an out-of-order line, a test-clip TC, Fig. 2, is inserted into the arrester-springs on the main-frame which is normally closed to connect up the line LL and the connector multiple FS. The clip carries two plugs LP, EP, which are plugged into a test-clerk's circuit comprising a test jack TJ, and the wires LL, FS are now connected over the springs of jack TJ and relay CO. Arrangements are made for stepping past a faulty private branch exchange line automatically or manually. Test clerk's operations on out-of-order line. On plugging into jack TJ the test clerk is connected to the line, relay CO operates, and the line is tested. If there is earth on the b wire, battery on the a wire, or a short-circuit key A is thrown, relay CO is locked, the plug withdrawn, and relay L operates over its right or left winding or both respectively. Relay M then operates to earth at key A over m3, l2, l1, and locks up over m2. Relay CO is held over keys C and A. For earth on the a wire or battery on the b wire, key B is thrown, similar operations taking place. When the fault is cleared, relays L, C release, in turn, and lamp SL lights. When the key is restored, the lamp is extinguished and relay M released. For an open-circuit, key A or B and key C are thrown to hold relay CO when the plug is withdrawn, hut relay L does not operate until the fault is cleared and the line LL is next looped. Relay M then operates releasing relays CO. L in turn, and. lamp SL lights. Call to out-of-order line. The connector, Fig. 1, identical with that shown in Specification. 271,142, comprises a slow-release relay E which de-energizes after a slow-release dialling relay so that the ringing generator is temporarily cut off from the b wire at e when switching relay H operates. Battery on the a wire however energizes relay IC, Fig. 2, since relay CO is operated, disconnecting the tone lead at ic and connecting up battery so that when relay E releases, ring cut-off relay F immediately operates to trip ring- ing and to disconnect relay IC so that out-of-order tone is connected to the b wire. Out-of-order P.B.X line, other than the last. In this case, the c wire is connected over the plug EP to earth at co4 to step the final selector on by means of an insulated plug tc. The c wire can be manually earthed at the main frame by an all-metal plug to mark a P.B.X. line non- selectable during testing. Normal call, Fig. 3. The pre-selector PS is identical with that described in Specification 266,037. In the connector FS, a relay DL is operated over its winding 1 before switching relay H and is held over its winding 2 after relay H operates by earth over the a wire until the cutoff relay T operates. Relay DL thus disconnects the ringing generator until relay T operates, preventing energization of line relay R. Relay DL holds up temporarily after switching through over winding 1 by reason of the slow-release of a control relay or by being itself slow-release.