Patent GB-190220237-A (GB)
Title: Improvements in Selective Calls for Telephones and Telegraphs.
Inventor: PALMER WILLIAM
Filed: 1902-09-16
Granted: 1903-04-30
Abstract: 20,237. Palmer, W., and McClintock, A. Sept. 16. Telegraph and telephone calls; telephone systems; telegraphs.-A selecting-system is arranged so that a central station can call any subscriber on a line, without ringing other bells ; all subscribers' telephones &c. are then short-circuited except that called. Normally all the telephones &c. are in circuit, so that a subscriber can call the central station. A subscriber's apparatus is shown in plan in Fig. 9, and in front view diagrammatically in Fig. 2. Fig. 13 shows a central-station switch for a group of subscribers ; a subscriber is called by first sending a succession of uni-directional currents in number corresponding to the subscriber's number, and then sending a reverse current. These currents pass through the coils R of a polarized relay in each subscriber's apparatus, having a pivoted armature R', Fig. 9, situated within the coils R, and between the poles of one or two permanent magnets M, with an arm r to touch either of two contacts r', r<2>. A local battery LB, Fig. 2, is thus connected to either of two electromagnets E, S, depending on the direction of the line current. The succession of currents first sent causes the magnet E to vibrate an armature P<1> and pallets in opposition to gravity, allowing an escapement wheel C to be turned by a spring motor a number of teeth corresponding to the number of currents sent. The reverse current then causes the magnet S to rock an armature lever K in opposition to gravity. A projection k on this lever enters a recess w in the escapement wheel C of one subscriber only, the notches being placed differently in the wheels of different subscriber's apparatus. A catch c on the lever K then releases a pivoted switch D, which falls on a spring F, and connects the local battery LB to the subscriber's bell A through the relay arm r and contact r'. The subscriber can then turn the switch D further by a handle, so that it presses a spring d<2> away from a contact d<3>, and is held by a hook at the end of the spring F ; the subscriber's telephone &c. is then left in circuit with the relay coils R and the line. In order that, normally, any subscriber may speak to the central station, the short-circuit across the telephones &c. includes a metal disc I, attached to the escapement wheel C, and in contact with a spring J. When the apparatus is not in use, a non-conducting sector i stands under the spring J and opens the short-circuit. Any movement of the escapement wheel in each apparatus displaces the sector i from under the spring J. The shaft of the escapement wheel carries a number dial under a notched cover, to show when the line is in use, and who is called. The lever K carries a stop x, which may engage a projection y on the escapement wheel C, and hold this tooth away from its normal position, so that the disc I maintains the short-circuit until the lever K is again rocked. After a call has been effected, currents sent from the central station place each escapement wheel in this position, with the projection y against the stop x, and the disc I shortcircuiting the telephones &c., except that called. The spring motor of the apparatus is wound by a shaft carrying a handle and a notched disc, which exposes the word "wind" when the spring is nearly run down. An arm H of the winding- shaft at the same time presses a spring G against a contact G<1>, so that the local battery LB is connected to the bell A through the relay arm r and contact r<2> each time any subscriber is called. The central-station switch, Fig. 13, consists of a num. ber dial O<1>, which can be turned by a handle with a switch arm N<1> over a ring of contacts, to send the desired number of successive currents. A central push button N<4>, normally pressed out by a spring, carries a reverser consisting of three rings N<7>, N<8>, N<2> under two springs N<11>, N<12> connected to line. In the position shown, current is sent from the central battery MB through the ring of contacts and arm N', and two rings N<8>, N<9> to line. When the button is pressed in, a contact is made at N<13> and a reverse current sent to line. The disc O<1> has two notches in its edge to receive a projection on a spring, and allow this to short-circuit the switch. One notch corresponds to the condition of the circuit while the line is in use after a call ; when the subscriber rings off, the button N' is pressed and the disc O<1> is turned one notch, causing all the levers K to move the stops x over the projections y, and the sectors i to stand under the springs J. The next notch then receives the short-circuiting spring, and the line is in its normal condition, in which any subscriber can call the central station. The subscribers have magnetocall generators with two-part commutators, to give intermittent currents in one direction, such as to cause the polarized relays to connect the switching- magnets S only.