Patent GB-250694-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1925-01-23
Abstract: 250,694. Automatic Telephone Manufacturing Co., Ltd., Ostline, J. E., and Edmunds, T. M. Jan. 23, 1925. Automatic and semi-automatic exchange systems.-The intermittent connection of battery potential to one of the speaking conductors at a selector to control a busy flash signal is made through that winding of the line relay which is normally connected to earth so that during the periods of battery connection both speaking conductors are at substantially the same potential. Since this results in the release of the line relay an additional circuit is provided for the release relay to prevent the release of the selector, this circuit being closed intermittently at periods corresponding to the battery connection to the speaking conductor. The invention is described in connection with a group selector which moves to eleventh terminals and gives a busy tone and busy flash signal if all trunks in a particular level are busy, and under such busy conditions the circuit of the vertical magnet is broken so that any further impulses which may be transmitted at this time are rendered ineffective. The busy tone and flash connections may be supplied over leads each common to a group of switches, these leads being in turn supplied from a busy tone transformer and an interrupter cam common to the whole exchange. The common leads are so connected up to alarm devices that a fault on a particular lead can be readily traced. First arrangement, Figs. 1 and 2. The vertical and rotary motions of the group selector Stake place in the usual manner, and if all the lines in the selected level are busy the wipers move into their eleventh positions and an earth connection over armatures E<2>, D4 operates a meter OFM connected to the eleventh test terminal before the stepping relay E is released. Relay D operates as for an idle line and holds open the circuit of the vertical magnet VM to prevent any further operation thereof. The springs V - - Z are operated at the eleventh step, springs V, W maintaining the connection of the line relay A to the speaking conductors after relay D has operated. Springs Z connect earth from conductor P over conductor 6 to the relay BR, which is common to a group of switches and is intermittently energized over the upper cam springs BCS. At the lower springs BCS battery and busy tone BT are alternately connected over common lead 5, spring Y, and the lower winding of relay A to the lower talking conductor, an additional circuit X, 7, 8 being completed by relay BR for relay B at the periods when the battery connection is made to conductor 5. In a modification, the busy tone is connected through separate transformer windings to a number of leads each common to a group of switches, and the lower springs BCS are replaced by extra contacts on the relay BR, each group of switches thus having separate busy tone and busy flash leads instead of using leads common to the whole exchange as in Fig. 2. In another modification, the relav BR is eliminated, and an extra winding on the release relay is directly energized from cam springs BCS. Second arrangement, Figs. 6 and 7. The springs 25 - - 27 are operated upon the eleventh rotary step, springs 27 short-circuiting the switching relay DR, which therefore does not operate, whilst springs U open the vertical magnet circuit. The apparatus below the dotted line, Fig. 7, is common to the whole exchange, the remaining apparatus in Fig. 7 being common to a group of switches. Relay BR<3> is intermittently operated over spring C1 and at each operation connects battery over fuse f, low-resistance upper winding of relay EAR<1>, lead BC, springs 25, and the lower winding of the line relay AR to the lower talking conductor. At the same time, battery is connected over lead HC and the upper winding of release relay BR to hold this latter relay energized. During the periods of de-energization of relay BR<3>, busy tone from coil BT<4> is supplied through transformer BT<3> to the lead BC. If an earth occurs on the lead IC, relay EAR closes an alarm circuit 50. An earth or lead BC causes fuse f to blow and give an alarm in known manner. An earth on the lower talking conductor causes the operation of relay EAR' which removes a short-circuit from its lower winding and closes a circuit for lamp Land alarm relay EAR<2>. An earth on lead HC causes fuse f tn blow, whilst a battery connection to lead BT<5> causes fuse f<1> to blow. The provision of links l - - l<3>, 14 - l<7>, l<8> - - l<11> facilitates the tracing of a faulty lead.