Patent GB-191327646-A (GB)
Title: Improved Circuit Arrangements for Telephone Systems.
Filed: 1913-12-01
Abstract: 27,646. Siemens & Halske Akt.-Ges. Nov. 30, 1912, [Convention date]. Semi - automatic exchange systems. - The operator applies a selectable potential to the test circuit of the wanted subscriber, and optionally also to that of the calling subscriber, and the desired connexion is then established automatically by hunting - switches. The arrangement is applicable to private branch exchanges, both for local connexions and, especially, for establishing incoming connexions from the main exchange. Outgoing connexions to the main exchange may be effected in the same way or by automatic devices operating independently of the operator, both methods being in some cases at the command of the subscriber. Fig. 7 represents a private branch exchange in which a connexion between a local line l1, l2 and a main exchange line a1, a2 is initiated by depressing keys NT, AT individual to the two lines, whereby hunting-switches W, W<1> at the ends of a link circuit are set in action and fasten themselves on the terminals of the two lines. An idle link circuit is selected beforehand by a switch V. In answer to a call from a sub-station N<1>, the operator plugs into the jack K1, and if the connexion desired is a local one she plugs the other end of the cord into the jack K2 of the wanted subscriber. If, however, a main-exchange connexion is desired, she depresses the keys NT, AT. A relay An is thus energized and completes the circuit of the driving-magnets D, D<1> of the switches W, W<1>, which hunt successively for the calling and wanted lines under control of the test relays C, P. The relays C, P are locked up independently of the keys NT, AT by the relays T, B, which are energized in series with them. The relay T disconnects the calling line from the jack K2 and relay R and lights a busy lamp RL, while the relay B energizes a lamp BL<1> (to mark the exchange line busy and indicate that the connexion is completed) and gives a call signal at the main exchange by bridging the line condenser K. The operator, observing the lamp BL<1>, releases the keys NT, AT, so that the relay An is de-energized and causes the switch V to move forward to the next idle link circuit. The connexion is released when the local subscriber hangs up his receiver, since the de-energization of the relay S opens the locked circuit of the relays B, P, and the deenergization of the relay P energizes a relay Q which opens the locked circuit of the relays C, T. When the call is from the main exchange to a local line, the calling signal AL<1> is given by the relay R<1>, which energizes a self-locking relay H. The operator presses a speaking key Sp and sets up the wanted connexion as already described by pressing the keys AT, NT. The energization of the relay B in this case completes the starting-circuit of a ringing-control switch RE, which energizes a ringing-relay L. While the switch RE is rotating, the relays P, B are kept energized in a circuit through the arm I, but if the switch RE regains its normal position before the subscriber has answered the call, the circuit of these relays is unlocked and the connexion is released. Means are provided for enabling the local operator to cut into the exchange conversation of a private branch subscriber. In a modified arrangement, suitable for a larger number of lines, the lines are divided into groups served by separate sets of switches, a link circuit in the proper group being selected by the operator. In other modifications, switches are employed which are individual to the local- and exchange lines, instead of being common to them as shown in Fig. 7.