Patent GB-221362-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1923-09-29
Abstract: 221,362. Coventry Automatic Telephones, Ltd., and Collyer, J. E. Sept. 29, 1923. Automatic and semi-automatic exchange systems; metering.-Talking current is supplied to a called line over two back-bridge relays, one connected. to each line wire, the simultaneous energization of the two relays when a called subscriber replies effecting the operation of the calling subscriber's meter, whilst if one relay operates a short time before the other as, for example, in the case of a call to a manual operator, metering is prevented owing to the release of a third relay. In the latter case the successive operation of the relays also transfers the control of the release of the connection to the operator. The invention is described with reference to a system in which the called line is fed with talking current from a first group selector, Fig. 1, which is of the type in which the rotary movement precedes the vertical movement. Call to ordinary subscriber. When the selector, Fig. 1, is seized, relays 12, 14 energize as usual, and the change-over relay 17 operates over rotary off-normal contacts 49, and connects dialling tone over its armature 21. The first set of impulses is repeated by relay 12 to the rotary magnet 1. At the first step, contacts 49 operate and complete a circuit 49, 25, 26 for relay 24 which locks up and energizes relay 28. Relay 24 also extinguishes lamp 19 which was lit upon the seizure of the selector so that the continued lighting of this lamp would indicate faulty use or operation of the selector. At the end of the digit, relay 17 which remained energized during the rotary movement over contacts 23, 22, de-energizes and completes a circuit 49, 25, 26, 7, 31, 32 for the vertical magnet 2 which raises the wipers one step. The operation of vertical off-normal contacts 7 connects magnet 2 and switching relay 32 in series whilst a point between the two is connected to the test wiper 4 so that if the wipers are resting on a busy trunk the relay 33 is shortcirouited and the magnet 2 raises the wipers a further step. The self-interrupting contacts 32 of magnet 2 are arranged as described in Specification 219,453, so that at the commencement of a stroke, a local energizing circuit is completed for the magnet over contacts 49, 25, 26 and the upper and lower springs 32. When an idle trunk is found, relay 33 energizes and extends the connection, and further impulses are repeated by line relav 12 over the lower trunk conductor. When the called subscriber replies, back-bridge relays 38, 39 energize over the called loop and unlock relay 24 which upon release completes a circuit 49, 25, 43, 42, 11 for operating the calling subscriber's meter. After a short interval, sufficient for the operation of the meter, relay 28 which remained locked over contacts 47, 46, 30, 29, 18, also deenergizes and opens the metering circuit. When the called subscriber hangs up, the release of relay 39 completes a circuit for lamp 19 in case of delay by the calling subscriber in replacing his receiver. Called line busy. A busy condition is characterized by the intermittent energization of relay 38 and the non-energization of relay 39 so that relay 24 remains locked up and metering cannot take place. Call to manual operator. When a call is extended to the operator's circuit shown in Fig. 2, relay 51 energizes in series with relay 39, lights lamp 56 and operates relay 55 which connects up a ring-back signal 58. Upon the insertion of a plug 60, relay 62 completes a circuit for relay 38, but relay 39 is disconnected at contacts 53, 67 and relay 24 therefore remains locked up. After a short interval, relay 28 falls back to prevent the completion of the metering circuit. After a longer interval relay 55 falls back, relay 38 remains energized over coil 69 and relay 39 energizes in series with supervisory relay 70. The release of relay 28 also completes a holding circuit 46, 30, 29, 18 for relay 14 which cannot therefore de-energize to release the connection until the plug 60 is withdrawn.