Patent GB-285947-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1926-10-29
Abstract: 285,947. Automatic Telephone Manufacturing Co., Ltd., and Passmore, W. O. Oct. 29, 1926. Automatic and semi-automatic exchange systems.-A local connection can be broken down by a toll operator, whether the wanted subscriber is the calling or called subscriber, or whether in the former case the called subscriber has answered or not, in response to the application uf the same potential to both speaking leads. This arrangement is stated to be applicable also to test clerks' circuits. The local connection includes a switch having two feeding-bridges, in the example described a rotary connector, in which each bridge comprises a relay connected between one lead and earth and an impedance coil between the other lead and battery, and in which feed to the calling party is reversed on the reply of the called party. Metering is effected for a local connection when the back-bridge relay D operates, due to the connection to the RT lead of battery over a resistance while a slowrelease relay, whose circuit is cut by relay D, releases. Setting up of connection by subscriber. On being taken into use relay A operates to battery over resistance 54 via the calling loop. Relays B, J pull up in turn and the latter locks up over armature 13. The next series of impulses is repeated to magnet V, and the last series to relay E and magnet R in series. Relay E disconnects the P1 wiper at 39, at 40 connects relay G to the P2 wiper, and at 41 forms an alternative impulsing circuit, since relay G will operate in passing over busy contacts. The wipers now engage the first line in the required P.B.X. group. All P.B.X. lines busy. The contacts for wipers P1, P2 on the private bank are strapped together in all positions but the last. If the first line is busy relay G operates over the earthed P2 wiper and locks up when relay F de-energizes. Relay C now operates (earth, wiper P1, 39, 35, 51, relay K, and shunt 54<1> in parallel, relay C, battery), and removes the shunt from relay K, which in turn pulls up. Magnet R now operates to earth at 17, advances the wipers to the next contacts, and de-energizes relay K, but not slowrelease relay C, and cuts the magnet circuit. Relay G remains energized over armature 24 and wiper P2. Relay G is. slightly slow-release to allow for failure of wiper P2 to bridge adjacent contacts. If there is no idle line, the wipers step to the last contacts, where absence of earth on wipers P1 releases relays K, C, and the busy signal is sent back from BS. The subscriber hangs up, relays A, B, G release in turn, and the switch returns to normal. Completion of call. When the wipers find an idle line, relays G, C de-energize, since there is battery instead of earth on the private wipers. and relay H energizes (battery, P2, 40, lower winding of H, 36, 24, 17, earth) and locks up over its upper winding. Ringing current is now sent from lead GEN, and ring-back tone over armature 44 and small condenser 52. When the called subscriber answers, relay F operates over its upper winding and locks over its lower winding. cutting off ringing current, and speaking current is connected from the upper winding of impedance coil I and the reversing coil D. Relay D reverses the current flow over the incoming line, battery to the positive conductor from the lower winding of I, and earth to the negative from relay A. The circuit of relay J is broken at 13, but before it releases, booster-battery from BM is connected over resistance 53 to conductor RT to operate the calling subscriber's meter. When relay J releases, battery on RT is replaced by earth at 33. Release. According to the Provisional Specification, release is under control of both parties. Regular connector. If wipers P1, P2 were not strapped together, the rotary connector could be used for dealing with individual lines. Trunk call for called subscriber. The toll operator obtains connection to his line, and puts earth on to the a and b conductors. Relay D is shorted, and at 14, releases relay B, thus releasing the preceding switches, after which relay A de-energizes and the connector returns to normal. Trunk call for calling subscriber. The operator earths both speaking conductors, so that relay A is shorted over one or the other, according to whether the called subscriber has or has not answered. In either case relays A, B de-energize, and the connection is released.