Patent GB-218722-A (GB)
Abstract: 218,722. Relay Automatic Telephone Co., Ltd., Edwards, W. D., and Vanneck, R. G. April 7, 1923. Automatic exchange systems.-A called subscriber by dialling a prefatory digit can transfer the calling subscriber's line to third party's line over the original connecting apparatus. According to the value of the prefatory digit the originally-called subscriber remains connected or is released. The invention is described as applied to a relay system in which a calling line is extended over a feed relay group to a temporarilyused recorder, which in response to dialling impulses marks out the wanted line, to which the feed relay group is then connected. The feed relay group is so modified that if the called party dials a prefatory digit a recorder is again taken into use and can be controlled to select a third party's line. Assuming that the feed relay group shown is taken into use bv an operator or by switching mechanism at a distant exchange, the line relay A<1> is energized over the B wire and completes a circuit 3 for a guard relay G, which energizes relays I, BBS, and earths a holding wire Hr to prepare the recorder for operation. Dialling impulses from the distant exchange are now repeated by the relay I over circuits 4a, 4b to the recorder, which in known manner marks out over a wire M and energizes a marking relay OTM which brings about the connection of the feed group to the wanted subscriber's line. If the called line is busy, the A line is earthed and the B line is connected to battery. The differential relay IS is therefore unbalanced and completes a circuit for the cut-off relay ICO which disconnects the relays I, BBS. The slow-release relay BBS holds for a short interval, during which a relay NU and the busy relay BB energize over the A and B wires respectively and lock up, connecting busy tone from the lead b<1>b to the repeater coils. In case the number called is a non- existing one, the A wire is earthed and the B wire is disconnected. The relays IS, ICO operate as before, but the busy relay BB remains inert and a special tone is transmitted to the calling party from the lead nu. If the called line is free the A wire is disconnected and the B wire is earthed, the relays IS, ICO energize, and the relays I, BBS relapse as in the case of a busy call, but the relay NU does not respond. When the called party answers, the connection is completed and talking current is supplied to him over the feed relays B<1>, B<2>. Relay B<1> closes a circuit for a relay C. Assuming that the called subscriber is, for example, a subscriber on a private branch exchange and desires to transfer the call to another party in the same branch exchange, he now dials a prefatory digit 1. The relapse of the relay B<1> completes a circuit 6 for a relay D which locks up, earths a second holding wire Hr2 to prepare a recorder for operation, and connects the impulse wires leading from the recorder to the windings of the relay IS. Relay IT energizes over the called subscriber's loop, closes a locking circuit for the relay C, energizes the relays Z, E, and closes an impulsing circuit 8 to the recorder. The called subscriber now dials the wanted number, which is repeated by the relay IT to the recorder, which marks out the wanted line and energizes a marking relay OTMX over the circuit 9. Relay OTMX locks up over circuit 10, energizes relay BBS, and opens the holding circuit of the first called line, thereby de-energizing the relay RCO, which transfers the marking circuit to the relay OTM and de-energizes the relay D. The recorder is now held over the holding wire Hr. The response of relay BBS causes the relapse in turn of the relays IT, C, OTMX, the latter relay completing the holding circuit over wire H for the newly-marked subscriber's line and energizing the relay RCO to release the recorder. The calling line is now extended to the third party's line which is tested as before. The transfer operation can be repeated as desired. By dialling a prefatory digit 2 the called party may transfer the call to a third subscriber and remain connected, the three subscribers then conversing together. As relay IT de-energizes twice, the slow-to-operate relay Z does not pull up until after the second impulse. After the first impulse therefore, when the relay E energizes, a circuit 12 is completed for a relay F, which provides holding battery for the first called connection over the circuit 13 and wire H on the energization of the relay OTMX.