Patent GB-251744-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1925-03-27
Abstract: 251,744. Siemens Bros. & Co., Ltd., and Berry, J. March 27, 1925. Automatic and semi-automatic exchange systems.-In a trunking system employing loop impulsing, at the repeater at the outgoing end of a trunk, the forward loop is broken after each train of impulses has been transmitted to enable supervisory signals to be sent back over one line wire, the switches at the distant end of the trunk being held over the other line wire. A delayed metering arrangement of the kind described in Specification 200,928 is employed in order to avoid operation of the meter by the busy flash signal. The invention is described with reference to a system in which connections are set up under control of a register-controller of the codetranslating type, with feed bridges at the first code selector and at the connector. First code selector, Fig. 1, and repeater, Fig. 2. The register-controller sends out impulses over contacts of relay KA, and test relay JB switches through when the selector seizes a trunk leading to the desired exchange. Line relay A and release relay B at the repeater energize, and at the first impulse, sluggish relay C operates to bridge the outgoing trunk, over which impulses are repeated at contact a3. Relay C falls back at the end of the impulse train, and reconnects relay DA to the b wire. This action is repeated for each train of impulses sent out. Intermediate selector, Fig. 3. This is seized bv the group selector in which the trunk terminates. The line relay AB also serves as the rotary stepping relay during the hunting movement. Line relay AB energizes initially over the a wire, and repeats loop impulses received over the trunk to the vertical magnet VM at contact ab1. Series relay CB (1) falls back at the end of the train, and connects up the rotary magnet RM. Relay AB is now disconnected from the incoming line, and interacts with the rotary magnet, being connected to the test wiper over contact rm thereof. Test relay T energizes when an idle connector is found, and extends the connection in the usual manner. All outlets busy. In this case, the wipers are driven to 11th terminals, and shaft contacts w1, w2, w3 are operated. Test relay T energizes as in the case of a free outlet, and connects up relay CB (2) over an interrupter, so that battery is intermittently connected to the b wire over contact cb4 and wiper B<1>, with busy tone in the intervening periods. Relay DA, Fig. 2 responds, and repeats back the interruptions to release the register-controller. Relay KA, Fig. 1, falls back, and connects relay D to the b wire to flash a lamp if the call has come from a manual position. Relay D is not operated long enough to affect metering. Line relay AB is maintained energized over the a wire and wiper A'. Connector, Fig. 4. The ring cut-off relay F serves to control busy signalling if the wanted line is engaged, and the same relay CC becomes connected in series with the vertical and rotary magnets VM, RM. Line relay AC energizes and repeats impulses at contact ac1. Series relay falls back at the end of the tens impulses and operates change-over relay G. When the final train of impulses has been received, relay CC relapses and connects up test relay H, which energizes if the wanted line is idle. When relay G falls back, ringing current is transmitted over ring cut-off relay F (1), which operates and locks upon reply of the called subscriber. Metering. Feed relay DC energizes over the called line, and connects battery to the b wire, operating relay DA. Fig. 2, line relay AC being held over the a wire. Relay D, Fig. 1 energizes over the b wire, and causes relays S, Z to operate under control of a cam timing-device to ground the metering wire m. Wanted line busy. Test relay H fails to energize, and when relay G falls back, ring cut-off relay F (2) operates, connecting intermittent battery to relay DC (1) at contact f5. Interrupted battery and busy tone are thus connectea to the b wire at contact dc1, causing relays DA, D to energize intermittently as before.