Patent GB-178134-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M5/08
Filed: 1922-04-10
Abstract: 178,134. Siemens & Halske Akt.-Ges. April 9, 1921, [Convention date]. Exchange systems.-In an order wire system in which a number of groups of trunks come from different exchanges, or from different groups of connecting devices in a single exchange, when a call is made over an order wire an idle trunk of the corresponding group is automatically selected by a switching device at the called exchange. The invention is described as applied to a system in which two manual exchanges I, II are connected to a semi-automatic exchange III by order wires DL1, DL2 and groups of trunks VLI, VLII, only one trunk in each group being shown. The exchange III may be a manual exchange. The trunks in both groups VLI, VLII are connected to the bank contacts of a singleco-ordinate switch W, Fig. 2, at the exchange III. Normally, all the trunks are marked busy in this switch, but when an operator at one of the exchanges I or II calls the operator at exchange III over an order wire, the trunks associated with that order wire are made selectable and the switch W rotates to engage an idle one, which is indicated by a lamp signal. The operator at exchange III then informs the operator at the calling exchange which trunk is to be taken into use, and operates her impulse sender, which is associated with the switch W to set up the required connection. The operation when a manual operator, say at exchange I, makes a call to exchange III, is described in greater detail hereafter. The depression of the order wire key DT1 energizes a relav C1 at exchange III, and a series circuit is closed for relays A1, Fig. 1, and G, Fig. 2. Relay A1 connects the operator's sets SPI, SPIII over the order wire DLI, and by closing contact 8, earths the sector 11 in the switch W, thereby marking the trunks VLI (which are connected in the first half of the contact bank) selectable. Relay G energizes a starting relay An, which closes the circuit of the stepping magnet D. The relay A1 also closes contact 7 which earths one end of the winding of the relay A2 associated with the trunks VLII in order that if the operator at exchange II depresses her key DT2 to make a call, the relay A2 is short-circuited and busy tone is transmitted over contacts 103, 104. When the switch W engages an idle trunk, relays P, V and T1 are energized in a circuit 8, 11, 19, 20, 22, 23, C11. Test relay P disconnects the stepping magnet D, and shortcircuits its high resistance winding to mark the trunk busy, whilst relay T1 close a circuit for a signal lamp FL1. Relay V energizes a relay H, which de-energizes the starting relay An. The operator at exchange III communicates the number of the seized trunk to the operator at exchange II, who plugs into the appropriate jack KL1, and short-circuits winding II of relay P, winding I of relay V, and winding III of relay II. Test relay P relapses and closes an energizing circuit for relay U, and a maintaining circuit for relay V, which extends from a contact 46 of the impulse sender, which the operator at exchange III is now actuating. Relay U maintains relay T1 energized, and connects the contacts 51, 52 of the impulse sender to the trunk 53, 54 over which the dialling impulses are transmitted. When these have been sent, the opening of contact 46 de-energizes the relays U and V, the former disconnecting the relay II at contact 47 and causing the calling line to be extended to the trunk 53, 54, and the latter deenergizing relay H to render the switch available for a new call. According to a modification, the trunks from the two exchanges I, II are alternately connected in the switch W or are mixed indiscriminately therein, the sectors 11, 12 being replaced by individual contacts, those of the same group being connected together.