Patent GB-190326850-A (GB)
Title: Selective Signalling Systems
Inventor: FAIRWEATHER WALLACE
Filed: 1903-12-08
Granted: 1904-06-23
Abstract: 26,850. Fairweather, W., [Stromberg Carlson Telephone Manufacturing Co.]. Dec. 8. Telephone sy stems; telephone calls.-Relates to selective signalling- devices on telephone party lines. In the diagram, 5, 6 represents an ordinary subscriber's line, and 29, 30 a party line, the circle X signalizing the presence of other subscribers on the same line. At each subscriber's station is a selective switching - a pparatus comprising a switch arm 41 carried on a shaft 40 and resting normally on a contact block 43. An electromagnet 35 with polarized armature is bridged across the line wires, and when a succession of currents from the battery 75 is sent to line by manipulating the calling key 71 at the exchange and repeatedly actuating the calling switch 72, the feed pawl 44 spaces forward the ratchet-wheel 39 and switch arm 41. A coiled spring is wound up during this movement. A reverse current sent to line actuates the armature of the electromagnet 35 in the opposite manner, and withdraws both the feed pawl and the detent pawl from the ratchet-wheel. The spring then returns the switch arm to the normal position. In this position, a trip arm 51 holds up the catch 49. At each station on the line a contact stud 59 is inserted in one of the holes in a metal ring 57, the position of the stud differing at all the stations. With the operator's cord circuit 20, 23 are associated a clearing annunciator 28, head set 25, magneto generator 27, battery 75, and seven switches or keys. These comprise an ordinary ringing-key 26 for use with non-party lines, a listening key 24, a selective calling key 71 which co-operates with the calling switch 72 as already described, a releasing-key 102 for sending the reverse current to line, and a ringing-key 89 for party line work. Assuming the operator to have received a call from subscriber A through the annunciator 15, and to have ascertained the number of the subscriber to be called up on the party line 29, 30, she inserts the plug 17 in the jack 31 and manipulates the selective calling key 71 to establish connection between the battery 75 and line through the switch 72. This switch is now actuated a number of times equal to that of the subscriber to be called, every back contact of the switch serving to short-circuit and discharge the line. The switch arms 41 at all the subscribers' stations are spaced round uniformly, but, when the prescribed number of current impulses has been sent, the switch arm at the called subscriber's station only is resting on the contact stud 59. The key 85 is now depressed, a battery current being sent through the key 71, sleeve side 23 of the cord circuit, sleeve side 29 of the line, conductors 81, 88, switch arm 41, stud 59, and electromagnet 52, returning by the ground G, G'. The electromagnet 52 being energized, the switch arm 54 is drawn forward and locked by the catch 49, contact being established not only between the switch arm 54 and contact 56 but also with the conductor 81 through the catch 49. The operator then proceeds to actuate the switch 72 repeatedly until all the switch arms have been advanced to their extreme limit beyond the reach of all the studs. Under these conditions the line is accessible to the called subscriber, all the others being locked out in consequence of the removal of the switch arms from the contact blocks 43. The call is completed by the operator manipulating the ringing-key 89 and sending ringing current from the generator through the sleeve side of the line, conductor 81, catch 49, switch arm 54, switch springs 93, 94, and bell 67, returning by the ground G, G'. At the conclusion of a conversation it is necessary for the operator to re-set all the instruments to the normal position before removing the plugs from the jacks. In order to give a warning signal if she fails to manipulate the releasing key for this purpose, a "dummy" selective apparatus 35<1> is provided at the exchange, in which a switch arm 41<1> is spaced forward in synchronism with those at the subscribers' stations. Unless this switch arm has been returned to its normal position on an insulating-block 109, by the manipulation of the releasing key, the return of the plug 17 to its socket will complete the circuit of the battery 118 through the contacts 119, 120, and switch arm 41<1>, and light up the lamp 117. Reference is made to Specification No. 26,848, A.D. 1903.