Patent GB-726969-A (GB)
Title: Improvements relating to automatic telephone systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1952-12-29
Abstract: 726,969. Automatic exchange systems. SIEMENS BROS. & CO., Ltd. Dec. 18, 1953 [Dec. 29, 1952], No. 32895/52. Class 40 (4). A plurality of selecting switches are adapted to be homed after use by common apparatus comprising an access switch or like device which has outlets to several selecting switches and is caused from time to time to traverse these outlets ; when an outlet is encountered which is connected to a selecting switch which is off-normal and not in use, that selecting switch is homed. The invention is described as applied to a system in which the selecting switches, Fig. 1 (not shown), have individual electric motors and latch magnets and are controlled by revertive impulses. When a selector is driven off-normal its off-normal contacts connect positive battery to wires ht and (over a high resistance) hst leading to the common homing circuit, Fig. 2. As further selectors move off-normal the rate of charge of a condenser HQ is increased. When a predetermined potential difference is reached, a cold-cathode tube HSV fires in series with a relay HST which operates to energize latch magnet HLM so that the access switch motor drives its wipers HS1-5 and operates its offnormal contacts HON1, HON2. Condenser HQ discharges and tube HSV is extinguished, relay HST holding over wiper HS1. The access switch rotates until it reaches an outlet to a selector which is off-normal, marked by positive battery on wire ht, whereupon a relay HTC operates to disconnect latch magnet HLM, stopping the access switch, and to initiate the slow release of relay HST. If the selector is in use in a connection in process of being set up, earth on the P-wire is extended over wire hp and wiper HS5 to operate a relay HT before HST releases, thereby causing a cold-cathode tube HCV to strike in series with a second winding of differential relay HTC which releases. If the selector is in use in an established connection, busy tone potential is encountered on wire hp. Relay HT acts as a transformer and, in conjunction with a rectifier HTR, fires a coldcathode tube HTDV. The consequent potential drop across resistance HCR causes tube HCV to strike and release relay HTC by differential action as described above. In either case, the release of HTC extinguishes tubes HCV and HTDV (if operated), prevents the release of relay HST, and re-operates latch magnet HLM so that the access switch is driven on until it encounters another off-normal selector which is similarly tested. When a selector is found which is off-normal and not in use, relay HTC remains operated and relay HST is released, connecting the positive battery on wire ht over wipers HS3 and HS4 to wire hl and thence to the latch magnet of the selector which is thereby driven to its normal position where the opening of the off-normal contacts removes the positive battery from wires ht and hst to release the latch magnet and relay HTC. Relay HST is re-operated over wiper HS1 and the access switch resumes its rotation. When it reaches its last contacts, relay HTC operates over wiper HS2 and is released by the ultimate release of relay HST, latch magnet HLM then being reenergized over off-normal contacts HON2 and wiper HS 1 to step the access switch to its normal position where the charging circuit of condenser HQ is again prepared. If any of the selectors are of the type having two sets of wipers and a wiper-switching relay, the common homing circuit is provided with an additional connection which short-circuits the wiper-switching relay when the selector is homed.