Patent GB-190610580-A (GB)
Title: Improvements relating to Telephone Exchange Systems.
Filed: 1906-05-05
Granted: 1907-05-04
Abstract: 10,580. Lake, H. H., [Stromberg-Carlson Telephone Manufacturing Co.]. May 5. Telephone systems; telephone calls.-Relates to the arrangement and construction.of the exchange apparatus in party-line telephone systems, whereby on the insertion of the calling-plug and depression of the key corresponding to the position of the station on the party-line, the proper signalling current is automatically connected with the line and is maintained in conn e x i o n until the subscriber answers, whereupon the current is automatically disconnected and the depressed key restored to its normal condition. The depressed key is locked in its depressed position by an electromagnetic device the circuit of which is controlled by a relay in the line-signalling circuit, which relay does not respond to the signalling-current until the called subscriber removes his receiver, thereby greatly reducing the resistance of the sub-station apparatus, whereupon the relay breaks the circuit of the locking-device and releases the depressed key. Fig. 4 shows the operator's listening and ringing key combined in one structure with the keys for a party-line having four subscribers, the switching-mechanism resembling that described in Specification No. 10,549, A.D. 1906. The key stems 9 are provided with cams 20 which just pass through openings 12 in a locking-bar 11, adapted to be moved to the right by the core 29 of the magnet 31. The depression of one of the keys 10 causes the springs 22, 23 to leave springs 44, 45 and engage springs 46, 47, thus completing the circuit of magnet 31 (as described later in connexion with Fig. 1), which then moves the bar 11 to the right. locking the key in its depressed position. When the magnet 31 is de-energized, the spring 25 on the stem of the key is able to move the locking-bar to the left to release the depressed key. The depression of any other key 10 also serves to release any depressed key. The listening-key 51 comprises a cam-plate 53 pivoted at 54, the lower part 56 having a flat portion 59, which, after actuation of the key, rests upon the roller 57 attached to the actuating-spring 58. An extension 61 on the locking-bar 11 engages a pin 60 extending from the side of the part 56, thus moving the locking-bar to the right when the listening-key, is depressed, and restoring the listening-key to its normal position when the depression of any key 10 moves the bar 11 to the left. The springs of the ringing-key 36 are controlled by the core of the magnet 31. The locking-bar slides in notches in the sides of the end plates 3, 4. Fig. 1 shows the general arrangement of a system using the switching-mechanism just described. The calling subscriber B is shown connected to the second subscriber on the party-line A. Subscriber B calls by removing his receiver, thus energizing the line relay 75 and lighting the lamp 78. The operator then inserts the answering-plug, closing two circuits -(a) from the battery S through the winding 79 of the supervisory relay, sleeve strand 80, and cut-off relay 77 to ground (b) from the battery S through the winding 79. sleeve strand 80, line a, sub-station apparatus, line b, tip strand 86, and winding 87 of the supervisory relay to ground. The supervisory relay is so arranged that when both windings are energized, contact-springs 90. 92 are out of contact and break the circuit of the supervisory lamp 95. When the subscriber's receiver is on his hook, the winding 79 only receives current and attracts its armature 93, allowing the armature 88 to fall, thus closing contact 90, 92. The operator then actuates the listening - key, closing an enquiry circuit from the receiver 98 through the springs 67, 64, tip strand 99, condenser 100, tip strand 86, line b, sub-station apparatus, line a, condenser 101, springs 58, 65, back to the receiver 98. Having learnt that a connexion is required with the second subscriber on the party-line A, the operator inserts the calling-plug and depresses the second key 10, thereby closing a circuit from the battery S through the wire 104, magnet 31, wire 105, springs 69, 68, contact 107, armature 108 of relay 124, wires 109, 110, springs 48, 49, and wire 111 back to the battery. The magnet 31 is thus caused to move the locking-bar 11 to the right, and to move the springs of the ringing-key into the position shown in Fig. 1, whereby the following signalling- circuit is completed : from the generator 113, through ring 116, segment 117<1> of the contact-ring 117, pilot relay 136, wire 121, springs 46, 22 of the depressed key, springs 44, 22 of the first key, wire 123, relay 134, springs 41, 37, tip of plug, line b, bell and condenser at the sub-station, line e, wire 131, springs 38, 42 of the ringing-key, springs 23, 45 of the first key, springs 23, 47 of the depressed key, wire 134, to the other side of the generator 113. The resistance of the bell and condenser at the sub-station makes this current too weak to energize the relay 124, but when the called subscriber removes his receiver, the resistance is greatly reduced, and the relay 124 is energized, thus breaking the circuit of the magnet 31 at the contact 107, whereupon the spring 25, Fig. 4, causes the cam 20 to move the locking-bar to the left, releasing the depressed key, and thereby breaking the circuit of the signalling-current. The contact-ring 117 is provided with a second segment 117<2> insulated from the first and adapted to connect the battery S to line in the intervals during which no current is supplied from the generator. This circuit is from the grounded side of the battery S, to the wire 135, ring 118, segment 117<2>, brush 120, wire 121, and through the circuit just described back to the wire 134, impedance coil 119, wire 111 to the battery. This direct-current circuit is normally broken by the sub-station condenser 129, but is completed when the subscriber removes his receiver, and serves to energize the relay 124 should the subscriber remove his receiver in the interval between successive periods of signalling-current. The pilot-relay 136 in the circuit above described controls the circuit of the pilot lamp 139 by which the operator can see the working condition of the ringing-circuit. When the two subscribers are in conversation, the talking-circuit includes the springs 64, 66 of the listening-key, and in order to prevent the interruption of the talking-circuit due to the opening of this contact when the operator listens in, these springs are shunted by the contact-springs 143, 144 associated with the called subscriber's supervisory relay. The talking-circuit under these conditions passes from the tip of the answering- plug to the condenser 100, wire 146, contacts 143, 144, wire 145, springs 39, 37, wire 126, tip of calling-plug, sub-station apparatus, wire 131, springs 38, 40, wires 154, 102, to the sleeve strand of the answering-plug. To enable the operator to make a " busy test," a test winding 148 is associated with the operator's induction coil and is connected to the spring 63 of the listening-key, and thence, when the key is depressed, by spring 66, and wires 151,145 to the tip of the calling-plug. The test is made in the usual way. A modified arrangement of the key-switching mechanism and circuits is described, in which each key 10 has only four springs.