Patent GB-367808-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-11-24
Abstract: 367,808. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, Liverpool, GILLINGS, C., 17, Everest Road, Eltham, London, and BELAS, F. T., 26, Arlescourt Road, West Derby, Liverpool. Nov. 24, 1930, No. 35356. [Class 40 (iv).] In a district-office system in which calls are established over a link circuit terminating in a call-finder (not shown) and a hunting switch JFS having access to main exchange junctions, to local switches and to an operator's position, a discriminator associated over a hunting switch DSF responds to the first two digits to operate selectively relays S, P, Q, which effect further hunting of the switch JFS if the call is not a main exchange one and prepare marking circuits in accordance with the zone of the wanted party for controlling multiple metering, which is effected by continuous rotation of the switch DSF during conversation. Discrimination. Line and release relays A, B energize when the call finder switches through, and relay MG operates and interacts with magnet DFM to step the switch DSF until an idle discriminator is found, when relay K energizes in series with relay 1A. The insertion of resistance YA serves to prevent simultaneous seizure of the same discriminator by two hunting switches. Relay J energizes and locks, completing the circuit for magnet JFM, which steps the switch JFS in search of an idle junction. Switching relay KK energizes when this :s found, and dialling tone is applied at the main exchange. If all the junctions are busy, the switch JFS stops in the eleventh position, and dialling tone is connected up by way of condenser QA. Relay 1A closes initial circuits for vertical and rotary series relays 1C, E and the first two digits operate the vertical and rotary magnets VM, RM of the discriminator. Relav C included in the impulse circuit completes a direct impulsing bridge across the junction and connects up relay MD. Assuming the digits denote a local call, the wipers of the discriminator are set on terminals such as the first of the group shown, and when relay E falls back, relays S, P energize, and the latter locks. Relay S operates only contacts s3, s6 at this stage, disconnecting relay KK, so that the switch JFS steps automatically until the local trunk group is reached, whereupon the circuit of relay S is opened and the switch hunts for an idle trunk in the usual manner. Switching relay KK reenergizes and connects up relay CO, which disconnects relav K to release the discriminator, and the switch DSF restores under control of stepping relay MG. Relay S now re-energizes and locks. If the digits denote a main exchange call, the wipers of the discriminators are set on terminals such as the second, third or fourth of the group, and either or both of relays P, Q energize but not relay S. Relay CO therefore energizes at once to release the discriminator. The last set of terminals of the group shows the wiring for unallotted positions in order to energize relays P, R. Relays KK, K are thus released and NU tone is connected to the calling line by way of condenser QB. Alternatively ground may be connected to the upper terminal to route the call to an operator. When the subscriber dials O, post springs NP are operated in the discriminator to energize relay S. Relay KK is disconnected and the switch JFS steps automatically until the group of junctions leading to the operator's position is reached, whereupon the circuit of relay S is opened and the switch hunts. If all trunks are busy in any of the groups, busy tone is applied to the calling line by way of condenser QC in the last position of the group. Metering. On the reply of the called party, shunt-field relay D responds and releases relay MD to initiate metering. Marking circuits controlled by relays P, Q in accordance with the tariff are completed to bank 3a of the switch DSF, and this switch rotates continuously under the control of stepping relay MG which is now connected to pulse wire 20. Each time a marked terminal is encountered, relay R energizes and sends a metering impulse over wire 21. Failure to dial. Relays TP, R energize in turn after an interval under the control of pulses from cams S, Z, releasing relays KK, K. Dialling tone is cut off and lamp LP lights. Release. When the calling party hangs up in a call completed over an operator's position, relay I re-energizes and holds relays J, MD to guard the link circuit until the operator clears. Relay I re-energizes momentarily in a similar manner should the calling party hang up during a busy flash period from the distant switches.