Patent GB-324952-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-11-06
Abstract: 324,952. Automatic Telephone Manufacturing Co., Ltd., Paulett, W. H., and Gillings, C. Nov. 6, 1928. Automatic exchange systems.- When the final switch in a train has been completely set the current flow in the circuit is reversed, the reversal being for a short period if the selected line is marked as free and intermittent if the line is not so marked. The reversal on a free line prepares metering circuits in the first switch of the train which become operative when the called party replies. Arrangements are made to prevent metering on operator calls. The feeding bridges and battery feeding relays are in the Fig. 2 (Prov.), or in the incoming selector, Fig. 6 (Comp), when the call is extended over a junction. Normal connection. The line switch, Fig. 1 (Comp.), on operation is stepped by the interrupter INT until a free line is reached when K operates switching the circuit through to the first selector, Fig. 2 (Prov.). Relay A operates over the calling loop, operating DA which enables B to pull up and breaks the circuit for DB. The first impulse series is repeated to V which raises the switch to the level required over which the wipers are stepped by R in series with INT until a free circuit is reached when H operates over front (or back as shown dotted) contacts of R switching the line through, resistance 37 being then substituted for V in the circuit C. The right hand winding of D is included in the loop to the intermediate selectors (not shown) which pass the call to the final selectors, Fig. 4 (Prov.). Relay A operates over the loop enabling B to pull up and the next digits are repeated to magnets V and R to set the final selector. The right hand winding of relay D, Fig. 2 (Prov.) is shorted by C during impulsing. Busy test, ringing and metering. If the line is not free relay H connected to wiper P does not operate and when C releases, after a slow release pause, G operates (37, 30, NR, 23) connecting busy signal consisting of interrupted battery and busy tone on the lower speaking conductor and resistance earth on the upper conductor. If the line is free however H operates from battery on wiper P, switching the circuit through, completing a circuit for D and breaking the circuit of E. E releases after a slow release pause connecting ringing to the called line but during the pause D operates reversing the flow of current in the calling loop and relay D, Fig. 2 (Prov.), operates releasing DA and operating DB. Relays S and MH are connected to the lower speaking lead and retard RI to the upper. When the called party replies S and MH operate over the called loop in the series with RI connecting MP to a pulsating earth on MPE. MP operates on the first pulse connecting a pulsating earth on MZE to relay MZ and to the meter wire M. MZ operates on the first pulse breaking the circuit of MP but this latter relay holds over ME until the pulse terminates to ensure complete registration. When the pulse terminates MP releases and remains disconnected since its circuit is broken by MZ. Busy signal : Busy signal is connected to the 11th bank contacts of all group selectors and consists, as in the case of line busy, of resistance earth on the upper and intermittent battery on the lower conductor. Relay D, Fig. 2 (Prov.), operates under these conditions connecting S and MH to the lower conductor and these relays pulse in synchronism with the busy signal. Relay MP operates but the interval between the earth connections on MPE and MZE is greater than the busy signal ensuring that metering on busy calls cannot occur. Call to operator. If a call is extended to an operator relay D operates when the operator plugs in but a resistance in the circuit allows relay S, Fig. 2 (Prov.), only to operate preventing metering and providing operator hold for relay B. Inter exchange working. The incoming selector, Fig. 6 (Comp.), is used when a call is extended over a junction, the low inductance relay A repeating the impulses received first to its own vertical magnet and subsequently over the loop, relay C shorting D during impulse transmission. If the called line is free relay D operates on the battery reversal releasing DA and operating DB which latter relay cuts out the. low impedance relay A and substitutes a reversed battery feed-bridge via AL and R2. When the called party replies S and MH operate allowing metering to be effected in the switch, Fig 2 (Prov). If the call is extended to an operator S operates but not MH as before and resistance 46 in the lower conductor prevents MH, Fig. 2 (Prov.) operating preventing metering and providing operator hold conditions. If busy signal is received it is repeated by S and MH to the first switch.