Patent GB-759589-A (GB)
Title: A telephone system comprising a satellite exchange and a main exchange
IPC: H04Q3/58
Filed: 1952-07-23
Abstract: 759,589. Automatic exchange systems. LICENTIA PATENT-VERWALTUNGS-GES. July 23, 1952 [July 23, 1951; Nov. 28, 1951], No. 18627/52. Class 40 (4). In an automatic satellite (non-exchange) supplied with current from the exchange, in order to distinguish between a calling line and an engaged line the satellite selector when functioning as a line finder tests over a circuit parallel to the line switching devices of the selector and including control means of the selector, the test circuit being disconnected when the call is extended. Relay selectors are used in which the line connecting relays are operated in turn under the control of two control relays. If either control relay is held operated the selector stops. Four systems each consisting of a satellite connected to an exchange by three junctions are described. In each system relays A, B are normally operated. The control circuits associated with one junction VL1 are shown in detail. Contacts between dotted lines enclosing areas denoted by II, III relate to relays associated with the other two junctions VL2, VL3. First system, Fig. 1. When satellite subscriber Tn3 makes a call, earth is applied over a back contact of the loop relay T3 to the common starting lead An which is connected to an idle junction. The exchange causes a relay D (not shown) in the satellite to operate and to release relay A which connects a relay selector RW to the wire a in place of the starting wire An. The selector RW is stepped by impulses from the exchange and at each step one or other of control relays S1 S2 is operated and releases before the next step is taken. When the selector relay 3 (not shown) associated with the calling line operates, a test circuit is closed which shunts the line switching contacts of the selector relay 3 and which includes a holding winding of the operated control relay S1 or S2. The non-release of the control relay S1 or S2 causes operations at the exchange which releases the satellite relay B and applies line current to the junction to operate the loop relay T3 which disconnects the loop from the test circuit. Relay F pulls up to disconnect the relay selector. Second system, Fig. 2. This differs from the first mainly in that the loop relays such as T3 are dispensed with. When subscriber Tn3 calls, the earth applied to the loop over back contacts of the selector relays 3 pertaining to the subscriber Tn3 is connected over the common starting wire An and relay D to wire b of an idle junction VL1. Relay D operates earth wire b, releases A and momentarily interrupts the earth connection over wire a to cause the exchange to transmit impulses over the wire a. The relay selector RW1 is stepped to the calling whereupon the operated control relay S1 is held in the test circuit which passes from the wire a over a front contact of relay 3 of relay selector RW1, back contacts of the relays 3 of the other relay selectors and the line loop to the earth connected to the junction wire b. Third system, Fig. 3 (not shown). This differs from the second system mainly in that some of the selector relay contacts are used when back to close the start circuit and to form part of the test circuit, and the operating windings of the selector control relays S1 S2 are included in the test circuit. Fourth system, Fig. 4 (not shown). As described in Specification 759,597, the even and odd numbered subscribers are grouped and the groups are connected alternately to the junction by the control relays S1 S2, so that only one line can be connected to the junction at a time. In addition to the test circuit containing the control relays S1 S2, there is a second test circuit including a test relay T (not shown) which before the line relay pertaining to a particular line operates, makes a test to ascertain whether a relay selector of another junction has connected up that line. If so, the relay T disconnects the first test circuit. Specifications 719,656, 727,586 and 759,656 also are referred to.