Patent GB-190327330-A (GB)
Title: Improvements in Electric Telephone Systems.
Inventor: FAIRWEATHER WALLACE
Filed: 1903-12-14
Granted: 1904-12-14
Abstract: 27,330. Fairweather, W., [Siromberg Carlson Telephone Manufacturing Co.]. Dec. 14. Telephone systems; telephone calls.-In telephone systems generally, and especially in party line systems of the step-by-step selective type, means are provided to short-circuit the receiver entirely at all the substations not desired to be connected with the line, so that conversation may not be heard by undesired people. The Figure shows two substations A, B connected up through the cord circuit C, this representing the final state of affairs and not the position at any intermediate time. At each substation, the electromagnet 1. actuates the switching-mechanism 3, comprising a ring 4, with holes 5 and a contact point 6, placed in a different hole at e a c h substation. The shaft 8 supports an insulated switch arm 11, adapted to engage, in its travel, the pin 6 and a contactpiece 7, disposed above the ring, but insulated therefrom. When the arm 11 engages the contactpiece 7, a notch 12 cut in the insulating-disc 10, is adapted to receive the ends of switch springs 13, 14 as shown at substation B. Springs 13, 14 constitute a switch s. The electromag - net 16 controls the switch lever 18, which normally does not engage the contacts 19 but, on passage of a current, is caused by the electromagnet 16 to do so, being retained in this position by a detent lever 20, the switch 22, 23 being thus separated as shown at substation A. These springs 22, 23 constitute a switch s<1>. The normal circuit conditions are shown at substation B, the arm 11 engaging contact 17, and the switch s being open while the switch s<1> is closed. The switches s, s' are included in a short circuit about the receiver 24, traced as follows :-From receiver 24 to switch s', wire 31, switch s, wires 32, 33, hook switch springs 26, secondary winding 35 to the receiver. A subscriber desiring connection actuates the generator 29, and then removes the receiver 24 from the hook. The operator inserts the calling plug 36 and ascertains the connection required. To lock out all other subscribers on the calling line, she depresses the calling key 38 and actuates a key 39 to right and left alternately, to step the switch arm 11 about the ring 4. When the key 39 is depressed to the right, the line is short-circuited, but when depressed to the left, a current passes through the following circuit : from the positive side of battery 43, wire 44, switch 39, calling key 38 to the tip of the calling plug. line wire 45, wire 33, electromagnet 1, wires 46, 47, jack 48, calling key 38, and thence to the negative side of the battery. The arm 11 is thus stepped forward till it engages the pin 6 at the calling substation. The operator now depresses key 50, which causes the receivers on the rest of the substations of the calling line to be short-circuited. The circuit completed at the calling substation is as follows : from the positive side of battery 43, to key 50, ground G, and thence to ground connection G', electromagnet 16, pin 6, arm 11, wires 46, 47, jack 48, calling key 38 to the negative side of the battery. As the arm 11 was stepped round the ring 4, the cam closed the switch s, but the shunt circuit round the receiver is opened again by the electromagnet 16 causing the switch s<1> to open. The talking .circuit which previously included the arm 11 and contact 7, is now closed by the lever 18, contact 19, and detent lever 20 which connects with wire 46, as does the arm 11. At other substations on the calling line, the switch s is closed, but, as the pin 6 is not in contact with the arm 11, the switch s<1> is not opened, so that the shunt circuit round the receiver remains closed. The operator now removes the calling plug from the line X, and connects it with the line Y, with which connection is desired. The other plug of the cord circuit is then connected with the line X, and the second subscriber connected up in the same way. On the termination of the conversation, the operator releases the calling key 38 and actuates the restoring key 55, which sends a current of opposite direction to the setting-up current, the electromagnets 1 being energized to withdraw the pawl mechanism 2, to allow the arm 11 to rotate back into engagement with the contact 7 under the action of a spring, as more fully described in Specification No. 26,850, A.D. 1903.