Patent GB-191417004-A (GB)
Title: Improvements in Machine Switching Telephone Systems.
Filed: 1914-07-17
Granted: 1915-05-20
Abstract: 17,004. Western Electric Co., [Woodward, F. T., (acting for Western Electric Co )]. July 17. Semi-automatic exchange systems.-Switches which act as automatic call - finders for connecting a calling line to a connecting- circuit are provided with manual setting- means, such as a knob 30 and pointer 31, Fig. 2, so that they can also be used by operators for completing a connexion from a connecting-circuit to a wanted line. The invention is described in its application to a private installation in which each subscriber has a set of keys for connecting his line to that of any other subscriber. The local interconnecting- devices are not shown, the invention being concerned with the means for connecting the subscribers' lines with public exchange lines 1, 2, Fig. 1, each of which terminates at the private installation in the wipers 6, 7 of a switch S of the sort described. Calls outgoing from the private installation. Each subscriber B has an exchange key AT, and his line is multipled in the terminal banks of the switches S. When the subscriber wishes to call the exchange, he presses the key AT, which remains automatically in a lock-down position until released at the termination of conversation. At the contact 50, 51, the key AT grounds a starting-circuit 13, which is common to all subscribers to whom exchange facilities are allowed, and thereby energizes a relay FR individual to the first idle exchange line. The relay FR locks itself up, completes a circuit for the holding-magnet HM and stepping-magnet SM of the switch S, and transfers the starting- circuit 13 to the relay FR of the next exchange line. A relay FVR, energized in parallel with the relay FR, serves to short-circuit the relays FR of the other exchange lines until the starting - circuit has been opened at the contact 50, 51, which is closed only while the key AT is in its fully depressed position and not in its locking position. The stepping-magnet SM intermittently short-circuits itself and advances the switch S until its wipers reach the line of the calling subscriber B, when a relay BR is energized over the test circuit 11<1>, grounded by the key AT, and short-circuits the magnet SM. The call is thus extended to the main exchange, where it is completed in the usual way. When conversation is finished, the subscriber B releases the key AT so as to deenergize the relay BR, and the stepping-magnet SM is brought into action again. When the switch S passes its last set of terminals, it opens a contact 20 so as to unlock the relay FR, and the holding-magnet HM is thus deenergized and permits a restoring-spring to return the switch to normal. Calls incoming from the public exchange. The application of ringing-current to an exchange line 1, 2 energizes a relay AR; which locks itself up, lights a call lamp L, and energizes an audible signal relay 41. A relay HR is also energized and closes the circuit of the relay FR, which locks itself up and transfers the circuit 13 to the next exchange line. In reply to the exchange call, the operator at the private installation presses a listening-key AS, which is locked in its depressed position by the energization of a magnet 3. (Any other key AS that may still be in a depressed position is unlocked by the momentary closing of a contact 58, 59, which short-circuits all the magnets 3.) Having ascertained which subscriber is wanted, the local operator moves the selector S to the terminals of his line, where it is held by the magnet HM, which is now energized through the contacts of the relay HR. Ringing-current is supplied in the usual way. The called subscriber answers by pressing the exchange key AT, thereby energizing the relay BR, which unlocks the relays AR, HR and the magnet 3 of the listening-key AS, the release of which completes the through-connexion. The holding- magnet HM is now kept energized by the relay BR. When conversation is finished, the called subscriber releases his exchange key AT, and the selector is restored as already described.