Patent GB-190610565-A (GB)
Title: Improvements relating to Telephone Exchange Systems.
Filed: 1906-05-05
Granted: 1907-04-18
Abstract: 10,565. Lake, H. H., [Stromberg-Carlson Telephone Manufacturing Co.]. May 5. Telephone systems.-Relates to the construction and arrangement of the supervisory relay apparatus in a common-battery telephone system. The supervisory lamps 45, 48 are each controlled by a compound relay consisting of two magnets 51, 52 with armature tongues 54, 53 separated by a stop 55 on the tongue 54. A spring 56, through an interposed insulating-column 57, tends to hold the armature 54, and with it the armature 53, column 61, and contact-spring 46, in a raised position, thus keeping the local circuit of the supervisory lamp 45 open between the contact-springs 46, 47. An additional contact-spring 58 on the compound relay associated with the calling-plug enables the operator to listen without disturbing the subscribers. The contact between the springs 41, 63 is shunted through a circuit comprising a spring 63, conductor 60, contact-spring 58, and conductor 59, to the tip strand 31 of the cord circuit, and enables the operator to converse with either or both subscribers. When the line-signalling lamp 25 is illuminated through the line relay 16, by the removal of the calling subscriber's receiver 6 from its hook 1, the operator inserts the answering-plug 26, closing the circuit leading from the negative pole of the battery through the winding 51 of the compound relay, thence through the sleeve strand 35, sleeve contact 33, thimble 20, and cut-off relay 22 to the positive pole of the battery. This energizes the cutoff relay 22 and the winding 51 of the compound relay and the latter attracts its armature 54 against the pressure of the spring 56. This would allow the second armature 53 to fall and illuminate the supervisory lamp 45 in a local circuit, including the contacts 46, 47, but that the second winding 52 of the compound relay is also energized through the circuit leading from the positive pole of the battery along the relay winding 52, tip stand 30, tip contact 28, tip spring 17, line limb 4, receiver hook 1, line limb 5, sleeve spring 19, sleeve strand 35, and compound relay winding 51 to the negative pole of the battery. The compound relay and supervisory lamp are controlled both by the answering plug and also by the calling subscriber. After learning the number of the subscriber to be called, the operator applies the tip 29 of the calling-plug 27 to the test thimble, meanwhile keeping the listening-key operative. If no click is heard, she inserts the calling-plug as the line is not busy, thus completing the circuit leading from the negative pole of the common battery through the winding 51<1> of the compound relay, and the conductor 62 to the section 36 of the sleeve strand, sleeve contact 34, test thimble 20, and the winding 21 of the cut-off relay 22 of the sub-station B, to the positive pole of the battery. The current flowing in this circuit energizes the cut-off relay 22, thus cutting out of circuit the line relay 16, and preventing the illumination of the line-signalling lamp 25. The same current also energizes the winding 51<1> which draws down the armature 54<1> and allows the upper armature 53<1> to fall, thus contacting the springs 49, 50 and illuminating the supervisory lamp 48. The lower contact through the spring 58 is also closed which shunts the contacts of the listening- key, allowing the operator to listen without interrupting the subscribers. On lifting his receiver, the subscriber extinguishes his supervisory lamp 48 by closing the circuit leading from the positive pole of the battery, through the winding 52<1>, conductor 60 to the section 31 of the tip strand, tip contact 29, tip spring 17, line limb 4, switch hook 1, line limb 5, sleeve spring 19, sleeve strand 36, conductor 62, and winding 51<1> to the negative pole of the battery, thus energizing the winding 51<1> to raise its armature 53<1> and to extinguish the lamp 48. The replacement of the subscriber's receivers on their hooks again lights the supervisory lamps, and the removal of the plugs of the cord circuit extinguishes them. When a connecting-plug is inserted in a line jack, all the associated multiple jacks are raised to the same potential, and thus a circuit may be completed through any test thimble and the test winding 43, to indicate to the operator the state of the line.