Patent GB-144320-A (GB)
Abstract: 144,320. Western Electric Co., (Assignees of Fowler, C. B.). Jan. 27, 1919, [Convention date]. Automatic and semi-automatic exchange systems and apparatus.-Relates to apparatus, specially adaptable for use during the period of transition from manual to full automatic working, by means of which operators may establish connexion between lines terminating at the manual exchange and subscribers of a distant automatic exchange. In addition to the ordinary cord circuits B for extending incoming lines to automatic exchange trunk lines, the operator's position is provided with a controlling connecting circuit A, which includes an impulse transmitter 11, and is manually connectable to one of the automatic trunk lines by means of a second jack 1 associated with each trunk line. This controlling circuit is rendered inoperative except when one of the ordinary cord circuits is also extended to the same trunk line. The insertion of plug 19 of the cord circuit B into the jack 4, of a trunk leading to the automatic exchange, operates relay 14 and lights lamp 17. Plug 20 of the connecting circuit A is then inserted into the second jack 1, associated with the trunk line, thereby energizing the relays 8, 16. Relay 8 connects the operator's telephone set S to the plug 20, whilst relay 16 disconnects the trunk conductors 29, 30 from the cord circuit B and connects them to the plug 20. The impulsesender 11 is then actuated to extend the trunk circuit C to the wanted line 2. The first actuation of the sender 11 closes the contact 12, thus energizing relay 10, which short-circuits the secondary and opens the primary of the coil 9. The contact 12 remains closed until the sender 11 is restored to normal, thus allowing the operator to attend to other calls during the period of selection. Upon restoration of the sender 11 to normal, the operator listens for the " busy " tone which will be heard if the line 2 is engaged. If the called line is idle, the plug 20 is removed, thereby de-energizing relays 8, 16, the release of which disconnects the operator's set from the. circuit A, and establishes connexion between con. ductors 29, 30 and the cord circuit B. At the same time, a bridge, including retardation coil 22 and relay 15, is connected across the conductors 29 and 30. The relay 15 is polarized and does not operate until the current in the trunk conductors is reversed upon the answer of the called station 2. The opening of the contact of relay 15 removes the short-circuit from the righthand winding of the relay 14, thereby increasing the resistance in the circuit of supervisory lamp 17, so as to extinguish the lamp and notify the operator that the called party has answered. The subsequent removal of plug 19 from jack 4 restores all apparatus to normal. If while the plug 20 is in the jack 1, and the calling device 11 is in its normal position, a listening key in another ordinary cord circuit is actuated, a relay 32 is operated and short-circuits the relav 8, thus removing the operator's telephone set from association with the circuit A, to prevent interference from " busy " tone to the operator or to the subscriber whose line might be connected to the cord circuit of the actuated listening key.