Patent GB-157938-A (GB)
Title: An arrangement for telephone installations with several trunk offices connected in series
IPC: H04M5/08
Filed: 1921-01-10
Abstract: 157,938. Siemens & Halske Akt.-Ges. Nov. 18, 1916, [Convention date]. Manual and automatic exchange systems.-In telephone systems in which several trunk offices are connected in series with one another over a single pair of trunks, and connection between offices which are not next to one another is effected over the trunks of the intermediate offices, a calling operator may automatically establish connection with a distant office without calling the intermediate offices. An installation of four offices A, B, C, D, Figs. 3 and 4, is described, each provided with a set of jacks K, appropriately designated by small letters to indicate with which office they obtain connection. To call an adjacent office the appropriate jack is plugged and ringing current is supplied to line. When it is desired to call an office next but one to the called office, plugging of the appropriate jack applies a selective potential to one trunk whereby a relay in the intermediate station is energized and the line automatically connected through to the called office. To call an office next but two to the calling office, plugging of the corresponding jack places a selective potential on both trunks, and relays are operated in both intermediate stations to extend the connection through to the called office. Supervisory lamps are provided at each office which show the condition of the various sections of the line, and connection must not be established if any of the sections passed over are already engaged, but in a modification in which connection between A and D may be established when B and C are already connected A and D are joined by direct trunks, and the plugging of the appropriate jack causes a selector Wb or Wc to seek an idle trunk leading direct to the wanted office. Means by which typical connections are established are described below. Connection between a terminal office and the next but one office. Assuming connection is desired from the offices A to C, if one of the jacks at the office A are plugged the section a, b is free, and the appropriate jack Kac is plugged. If the other section a1, b2 is also free, a circuit is completed through the relays R2 and DR1. Relay R2 closes a contact 10 and lights the lamp Sac, whilst relay DR1 interrupts the circuit of the annunciators K2, K3 at office B and extends the connection over B to C at contacts 12, 13, 14. Application of ringing current to the line will operate the annunciator K4 at office C. Should the trunks a1, b1 be engaged, the circuit of the relays R2, DR1 will be broken at contact 6 or 7 by the plugging of jack Kbc or Kbd, and the lamp Sac will not glow. Connection between an intermediate office and a next but one office. Assuming connection is desired from office B to D, if the jacks Kbc and Kbd are free, the jack Kbd is plugged, and provided the sections a1b1 and a2b2 are not engaged, the relays R3 and DR2 are energized. Relays R3 closes a contact 32 which causes the glowing of lamp Sbd, whilst relay DR2 disconnects the annunciators K4, K5 of office C and extends the line through this office to D. If the trunks c2, b2 are engaged by a connection between C and D, the jack Kcd will be plugged, and the circuit of relav R3 broken at contact 20, or if the trunks a1, b1 and a2, b2 are already seized by a connection between A and D, the relay DR1 will be energized and the circuit of the lamp Sbd broken at contact 34. Connection between two terminal offices such as from A. to D. The section a, b is free if the jacks at office A are unplugged. When the plug is inserted in jack Kad, if jacks Kbc and Kbd and therefore the line a, b, are free, the relays R2 and DR:. are energized, thereby lighting the lamp Sac and extending the line through office B. The closure of contact 12 also completes a circuit through relays R1 and DR2. Relay R1 breaks the circuit of lamp Sac and causes the illumination of Sad, whilst relay DR2 extends the connection to office D. If the section a2b2 were engaged by a connection between C and D, the jack Kcd would be plugged and the circuit of relay R1 interrupted at contact 20. Connection between A and D when there already exists a connection between B and C. On plugging jack Kad to establish connection from A to D, the relays R1 and E are energized over a circuit including the contacts 29 and 40, jack Kbc being occupied. Relay R1 lights lamp La at office A, whilst relay E locks itself over armature 48 and performs the following operations, (1) prepares circuit of stopping relay P, (2) disconnects the section ab from the office B, (3) causes the illumination of supervisory lamp Lb at office B, (4) energizes the rotary magnet M which steps round the wipers of the switch Wb. When the wiper 50 engages the grounded contact 51, the stopping relay P is energized, the switch becomes stationary and the section ab is extended to the office D over the conductors n1, m1. Relay G is also energized and lights the supervisory lamp Lc at office C. Removal of the operator's plug from jack Kad at the end of the conversation causes the relapse of relays E and G, the rotary magnet M is thereby energized and the switch. Wb restored to normal.