Patent GB-176384-A (GB)
Abstract: 176,384. M³ller, W. March 4, 1921, [Convention date]. Semi-automatic exchange systems.-In a district-office or like system in which calls between a district-office and a manual main exchange are made over trunks which terminate at both ends in non-numerical switches having terminals individual to the lines at the district office, both incoming and outgoing calls are made over the same trunks. In the system shown in Fig. 5, when a call is made from a substation on a district office K to the main exchange A, a callfinder at the district-office, associated with an idle trunk 5, is rotated to find the calling line, and at the same time a call-finder at the other end of the trunk at the main exchange is synchronously stepped round to engage contacts individual to the calling-line leading to multiple jacks on the exchange switchboard, a calling-lamp thereat also being illuminated. Calls from the main exchange A are dealt with in just the same way as if the wanted subscribers were wired directlv to the main exchange. When an operator inserts a calling-plug in the jack individual to a wanted district-office subscriber, connection is made to an idle trunk by an associated call-finder at the exchange, the call-finder at the district-office end of the trunk being synchronously rotated to extend the trunk to the wanted subscriber. If the call-finders at the two ends of a trunk become out of synchronism, both are arrested and a trouble lamp at the exchange is illuminated. Calls from district-office to main exchange. A calling district-office subscriber, on removing his receiver, completes a circuit for a starting relay 12 at the main exchange, a source of alternating current 30 thereby being connected to the rotary magnets 1, 2 of the district-office and main exchange call-finders sssociated with the first trunk 5. (If this trunk had been busy, the guard relay 7 would have been energized and the current source 30 connected over contacts 58, 59 and conductors 60, 61 with the call-finders of the next trunk.) A supervisory lamp 75 is also illuminated. When the wiper d of the district-office call-finder arrives at the contact of the calling line, a circuit 25, 24, a<1>, b<1>, k<1>, 11 is completed for the test relay 4, which short-circuits a portion of its winding to mark the calling line busy, and energizes a relay 13 at the main exchange over the wire c of the trunk 5. The relav 13 completes circuits for (1) the calling-lamp 57 and (2) the guard relay 7, which extends the trunk to multiple jacks on the switchboard over contacts 62, 63 and wipers a, b, and disconnects the current supply 30 to the rotary magnets 1, 2 at contacts 46, 47. When an exchange operator plugs into the calling jack, potential is applied to the sleeve wire 64, energizing a test relay 15, which short-circuits a part of its winding to mark the calling line busy at the exchange, disconnects the lamp 57, and energizes a switching relay 6 at the district-office. The relay 6 extends the calling line to the trunk wires a, b, over contacts 67, 68, and completes a circuit for the cut-off relay 3, thereby de-energizing the starting relay 12 and disconnecting the alternating current supply 30. When the calling plug is removed the relays 13, 7, 6 and 3 de-energize in the order named, rendering the trunk available for another call. Calls frori main exchange to district-office. On the appropriate jack being plugged a starting relay 4, having separate windings for each of a group of.calling jerks, is energized over the sleeve wire 64, and connects up the alternating current source 30. Both call-finders rotate until the exchange call-finder engages the contacts of the calling jack when the test relay 15 is energized, causing the response of the relays 13, 6, 7, 3, and the connection of the exchange operator to the wanted subscriber in a manner similar to that described in the previous paragraph. Indicating out-of-synchronism of two callfinders. For this purpose additional wipers c are provided, connected with one another over a simplex circuit including the wires a, b of the trunks 5, and a relay 16. The contacts engaged by these wipers are alternately earthed and connected to battery, so that if one switch gains upon the other to the extent of a contact, the relay 16 is energized to light a trouble signal 17 and disconnect the supply current 30 from both driving-magnets 1, 2. The following modifications are referred to:- (1) A separate trunk may be used for long-distance calls, arranged to be taken into use by the operation of a marginal relay: (2) instead of rotating the call-finders in synchronism, one may first be rotated to find a calling line or plug, rotation of the other to engage the corresponding contacts then taking place; (3) the call-finders of all the trunks may hunt simultaneously, the one first engaging calling contacts completing the connection; (4) continuously hunting call-finders mav be provided; (5) for trunk line traffic a subscriber may be provided with separate leads for conveying incoming and outgoing speech current, in which case he is allotted two sets of contacts in the banks of the rotary switches.