Patent GB-337515-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q1/32
Filed: 1929-08-28
Abstract: 337,515. Siemens Bros. & Co., Ltd., Christian, D. A., and Patterson, W. G. Aug. 28, 1929. Automatic exchange systems; metering.-In a system for working between exchanges respectively responding to loop and leg supervisory and control signals, the selectors are arranged to present either system on the outgoing side of the feeding bridge, the system selected depending on a signal received from a subsequent point in the switch train. As described a loop system is presented from the first selector which can revert to a leg system if and when it is definitely decided that leg supervisory signals are to be received. This reversion may take place when any switch in the train selects a level leading to leg exchanges only, or when the final selector has been set on the called line. Metering on called party reply is arranged for, a delay being provided to prevent metering on false signals. Local call. When the first selector, Fig. 1, is seized, relay A operates energizing V which enables D to pull up. Dialling tone is returned over d3 and BC energizes completing a loop on the outgoing side of the speaking bridge. The first digit is repeated by A to the vertical magnet VM stepping the switch to the level required. C operates on the first impulse and holds during the train; off normal springs k change over and L pulls up. At the end of the train D releases and RM steps the switch wipers over the selected bank. C falls away but BC is held in series with RM. When a free selector is found T energizes breaking the circuit of RM and switching through. BC, being slow to release, does not fall away at once. The essential parts of the intermediate and final selectors are shown in Fig. 3. Relay RC energizes in series with AA, Fig. 3, completing a holding circuit for BC to maintain the loop conditions on the outgoing side of the bridge. The next impulse series is repeated by A over the loop, relay C energizing to provide an alternate hold circuit for BC. When the final selector is taken into use RC remains operated in series with AF. At the end of the last digit train however, as contacts dd and rotary off normal contact w are open, RC releases and BC falls away re-establishing leg conditions. When the called subscriber replies Y and RC energize. RC has no effect at this stage but Y de-energizes L and prepares the delay metering device. When the called subscriber hangs up Y releases followed by Z and when the calling subscriber releases A falls back, V and T de-energize and ZM operates to release the switch. Called subscriber busy. If the called subscriber is found to be busy Y will not be held operated. Busy tone and flash will be received from the final selector, operating Y intermittently, but the period of the metering contacts o, n, the operation of which is described later, is arranged to prevent metering under flashing conditions. Call extended to a loop exchange. If the call is routed to an exchange at which loop impulses are required, relay RC remains operated holding BC energized until the final selector is set. The answering supervisory signal in such circumstances is usually battery reversal to which RY would respond. Relay RY performs the same functions as relay Y the contacts of the two relays being in parallel or series dependent on whether they perform closing or opening functions respectively. Reversion before final stage. The selector may be arranged to revert to leg working before the exchange to be served is reached. In such cases the selectors are provided with special vertical wipers which are arranged to release RC when a level serving only leg system exchanges has been chosen and the necessary circuit arrangements are detailed in the Specification. An incoming selector arranged to maintain loop conditions at the outgoing exchange until the requirements of the final selector have been ascertained and then to control reversion to leg working if necessary is also described. Metering. Metering is controlled by relay Y or RY dependent on whether the exchange called is of the leg or loop system. Contacts o and n are alternately closed, the interval between closure being sufficient to ensure that the supervisory relay is steadily energized. When o closes, S energizes, locking over its second winding and preparing a circuit for Z which pulls up when contacts n are made. Z locks up for the duration of the call and opens the circuit of S which latter relay holds, whilst n is closed over its winding (iii) in series with Z. Whilst both S and Z are energized booster battery is connected to the c-wire to meter the call. When n opens, S relapses and cannot re-operate during the duration of the call.