Patent GB-174641-A (GB)
Abstract: 174,641. Siemens & Halske Akt.-Ges. Jan. 31, 1921, [Convention date]. Automatic exchange systems. - Relates to systems in which the wanted line a, b is selected over a setting route by numerical switches IIIGW, LW, the speaking connection being then set up over non-numerical switches IVW, IIVW, in tandem and the setting route released. The test circuits of the non-numerical switches IVW of the first stage are so arranged that they cannot take into use switches IIVW of the second stage unless the latter have access to the calling trunk SS. The testing operations are controlled by an assignor VO, which may connect itself to tne switch IIIGW as shown in Fig. 2, or may connect itself to the connector LW, in which case the relay for testing the wanted line may be associated with the assignor instead of with the connector. The secondary switches IIVW have access to groupselectors IGW as well as to calling-trunks SS, and the means for rendering them non-selectable, when all the group-selectors to which they have access are engaged, is made inoperative, while the speaking route is being set up, at those switches which have access to the calling trunk. Selection of wanted line. When the trunk SS is taken into use by a selector IIGW, the relay C causes the magnet S to move the side-switch (represented by the four sets of contacts 1, 2, 3, 4) into its second position in which a relay R energizes the rotary magnet D1 of a call-finder AS. When the calling trunk is found, the test relay P energizes relay C2, and connects the relay A1 of selector IIIGW to the a lead of the incoming trunk and relay B1 over contacts 20, 26 to battery. The next digit impulses are repeated by relay A1 to the lifting-magnet H, after which relay B opens the circuit of relay B1, which energizes the rotary magnet D2. When an idle connector is found, the relays P1, C3 energize, and the leads a<1>, b<1> are extended to the relays A2, B2. The next digit impulses are repeated by relay A2 to the lifting- magnet HI, after which relay B2 energizes the change-over relay U over its winding I, so that the final set of impulses is repeated to the rotary magnet D3 over winding II of relay U. If the selected line is free, the test relay P2 is energized over its windings I, II, lead 53, normal contact 54 of the pre-selector IVW of the selected line, wiper 55, and relay T1. Establishment of speaking route. The test relay P2 connects battery over a low resistance 63 and contacts 62, 64 to the test circuit including windings II of relays PI, B1. The strengthening uf the current in this circuit energizes relay B1, which, by closing contact 67, energizes a relay R1 of the assignor VO. When its wipers find the trunk a<1>, b<1>, the test relay P3 energizes and connects ground to lead a<1> and battery to lead b<1>, thereby energizing relay A of trunk SS over lead 22, and relays A2, B2, which in turn connect earth and battery over wires 79, 83 to the called line, relay B2 at the same time opening at contact 51 the circuit including the test relay P2, lead 53, and cut-off relay T1. Relay P2 remains energized over its winding III but relay T1 reconnects the line relay R3 to the leads 79, 83, so that relay R3 energizes the rotary magnet D5 of switch IVW. When this finds an idle secondary switch IIVW, switch IVW is arrested owing to cut-off relay T1 energizing in series with relay R4, but if the switch IIVW has not access to the calling trunk SS, the switch IVW moves on to the next free switch IIVW. This is determined as follows :-The relay A being energized over the upper wiper of the assignor VO, and the relay B being de-energized, a circuit is closed over contacts 88, 89 for a group relay GU which connects battery to contact 101 of relay A3 in all switches IIVW having access to the trunk SS. When the switch IIVW finds an idle switch IIVW, the relay A3 of the latter is energized over its upper winding and lead 79, and if this switch IIVW has access to the calling trunk, the circuit of relay T1 is maintained over both windings of relay R4 and contacts 101, 90. The relay A3 also switches the test relay T2 from wiper 102, over which idle selectors for outgoing calls are found, to wiper 103 which tests terminals leading to incoming trunks such as SS. Relay R4 energizes the rotary magnet D6 which rotates switch IIVW until the trunk SS is found, when the test relay T2 energizes over a circuit including relay C1, contacts 111, 110, winding II of relay A3, windings II, I of relay T2, upper winding of relay R4, and winding II of relay T1. Relay C1 locks up so as to be independent of relays A, B, and relay T2 disconnects the rotary magnet D6 and completes the speaking circuit. If the switch IIVW has not access to the calling trunk SS, the circuit of relay T1 is opened when relay A3 is energized, and the switch IVW is moved on to the next free switch IIVW. If all the group-selectors, to which the switch IIVW has access for outgoing calls, are engaged, a relay G marks the switch non-selectable by opening contact 92, but the switch is made selectable for setting up incoming calls by the closure of contact 91 by the group relay GU. Release of setting route and assignor. The energization of relay C1 moves the side-switch into its third position, opening the circuit of relay P of the finder AS. Relays C2, PI, C3, P2, P3 de-energize euccessively and the switches of the setting route are released. Ringing current. In the third position of theside-switch, ringing-current is applied to the called line over ringing-relay U1 at the repeater Ue;- when the subscriber answers, relay U1 moves the side-switch into its fourth position, completing the talking circuit. Release. At the end of the conversation, thecircuit of relay C is opened in known manner thereby short-circuiting relay C1 to open contact 113 in the test circuit of switch IVW, IIVW.