Patent GB-170308-A (GB)
Abstract: 170,308. Siemens & Halske Akt.-Ges. Oct. 16, 1920, [Convention date]. Automatic and semi-automatic exchange systems and apparatus.-In district office and like systems in which connections between subscribers in the same sub-office are completed without tieing up the main office trunks, a single co-ordinate switch, associated with each trunk or group of trunks leading to the main office, responds to a predetermined set or sets of impulses to cause the disconnection of the trunk first taken into use, and effect such circuit alterations that the connection is extended to switches or lines individual to the sub-office. Two arrangements are shown in Figs. 1 and 2 respectively. In the first arrangement, Fig. 1, a calling subscriber Ta is connected over first and second preselctors IVW, IIVW, a repeater UE, and trunk-finder ZW, to an idle trunk TK, TK<1> leading to the main office, and the single co-ordinate switch MLW, after responding to the first two digits, is adapted to extend connection itself to switches individual to the sub-office. In the second arrangement, Fig. 2, the second preselector IIVW is provided with two sets of contacts, one allotted to main office trunks and the other to trunks leading to local selectors. The preselector IIVW first finds an idle main office trunk, in the first set of contacts, the auxiliary switch MLW then responding to the two digits to cause a switching relay U to energize and transfer the test circuit of the relay T<1> to an additional test wiper c<1>, after which the preselector IIVW continues its rotation and selects an idle one of the second set of trunks individual to the sub-office. First arrangement. The response of the line relay A in the repeater UE energizes a slow acting relay V which prepares a circuit for a control relay V<1>, which remains energized during the dialling of impulses. On the first dialling impulses being transmitted the rotary magnet D<3> of the switch MLW is energized over a circuit 37, V<2>, o, 19, 18, and after the wiper dm has left the contact o, over the contact 26. All the subscribers in the sub-office are allotted numbers prefixed by the digits 25, so that if, as is assumed, a local call is being made, the wipers of the switch MLW, in addition to those of the first selector (not shown) in the main office, will first be advanced two steps. After the first digit has been dialled a relay O<1> is energized in a circuit 20, 21, 22, 23, P, 24 and locks up over the contact 25. During the transmission of the second series of impulses the rotary magnet D<3> is first energized over the contact 27 and then over the contact 26, and the wipers of the switch MLW are advanced to the seventh contact, in which position the relay N is energized over the contacts 30, 31, 32 and locked up over the contact 33. The circuit of the test relay T<2> of the trunk finder LW is broken by the relay N at contact 9, and the trunk finder is released in known manner. Tie magnet D<3> remains energized over the contact 34, and continues to rotate the wipers until the teath contact is reached, where they begin to seel for an idle trunk leading to the local selectors. When an idle trunk is found the test relay P responds and, (1) short circuits its high resistance lower winding to mark the seized trunk busy, (2) disconnects the rotary magnet D<3>, and (3) extends the calling line to the first selector at the local sub-office over the armatures 38, 39. If all the local trunks are engaged, the switch runs as far as the last contact 43 where it comes to a standstill, and at the same time busy tone ET is connected to a third winding III of the line relay A. Release is effected on the relapse of the relay V after the calling subscriber has replaced his receiver, a circuit 41, 40, 42, 37, being thereby completed for the rotary magnet D<3>, which restores the switch BLW to its normal position. Second arrangement. A calling line is extended over first and second pro-selectors IVW, IIVW to an idle main office trunk VL, and the auxiliary switch MLW is operated by the first two digits as described in the previous paragraph. On the response of relay N a resistance w<1>, included in the holding circuit of the pre-selector IVW, is short circuited, and the consequent increase in current over the test wiper c, causes the energization of a normally inert switching relay U, which locks up over its lower winding and transfers the test circuit of the relay T<1> to an additional wiper c<1>. The test relay T' is now de-energized and completes a circuit for the rotary magnet D<1>, which rotates the pre-selector IIVW to seek an idle one of a second set of trunks leading to the local group selectors IIIGW.