Patent GB-190326848-A (GB)
Title: Telephone Systems
Inventor: FAIRWEATHER WALLACE
Filed: 1903-12-08
Granted: 1904-05-05
Abstract: 26,848. Fairweather, W., [Stromberg Carlson Telephone Manufacturing Co.]. Dec. 8. Telephone systems; telephone calls.-Relates to a party line system in which an exchange or central operator is used as an intermediary between the subscribers, whether they are on the same party line or not. The selective signalling devices are of the step-by-step type, and provision is made for locking out all the other subscribers on the line or lines while any two of them are in conversation. The apparatus at the various subscribers' stations is bridged across the common party line. Figs. 1 and 3 show the selective switching apparatus which is installed at each subscriber's station. The armature 32 of the electromagnet 29 is polarized by a permanent magnet 41 so that it is attracted to one or other of the cores 30 according to the direction of the energizing current. The armature is rigidly connected with a lever 34 pivoted at 33 and bearing a pawl 35 engaging with a ratchet-wheel 24 on a shaft 23. A succession of currents in one direction effects the step-by-step rotation of the shaft 23 and the switch arm 25 which it carries, a helical spring on the shaft 23 being coiled up during the rotation. A current in the opposite direction effects the disengagement of the pawl 35 and the detent pawl 36 from the ratchet-wheel 24, and the switch arm 25 flies back to the normal position, in which a stop arm 26 rests against a pin 27 and the switch arm makes contact with an insulated contact block 54. The switch arm revolves above an insulated metal ring 52 provided with as many screw-threaded holes 53 as there are subscribers on the party line. A contact stud 55 is screwed into one of these holes, its position being different at each subscriber's station. The second step of the switch arm brings it over the first of these holes, and at one of the succeeding steps it makes contact with the stud 55. On the same base-plate 20 is mounted a switch consisting of an electromagnet 65 and contact plates 61, 59. A spring-tensioned locking-catch 73 is adapted to maintain contact between the plates 61, 59, but a projecting piece 76 is formed on the hub of the ratchetwheel 24 so that, when the switch arm 25 flies back to the normal position, the catch 73 is moved aside and the aforesaid contact is broken. A signal disc is normally covered by a shutter carried by the shaft 23. The shafts 23 are rotated at all the substations in unison when any one of them is connected to line for conversation, and the disc is consequently exposed at all the substations, and serves as a "busy" signal. Figs. 6 and 7 show the "auto- "matic selector" used at the central station or exchange. This selector is employed for sending the intermittent unidirectional currents which actuate the switch arms at the subscribers' stations, and also for making the contact which energizes the electromagnet 65 of the selected subscriber, and bridges his instrument across the line. An insulated metal ring 81 is provided with a series of holes 82 into any one of which may be inserted one of the selector pins 83. A shaft 85 carries a crank and handle 88. When the operator desires to connect a subscriber's instrument to line, she inserts a selector pin in the hole corresponding to his number and turns the crank handle round in the clockwise direction until it reaches the stop 102. In so doing, a spring is wound up which, when the crank handle is released, restores it to the normal position, and drives also, through ratchet gearing, clockwork mechanism which gives movement to a shaft 103. This shaft bears a cam 109 of hard rubber which sets the switch tongue 112 in vibration, the function of which is alternately to send a current impulse to line and to short-circuit the bi-metallic line in the intervals. As the crank arm passes the selector pin which has been set, a spring - controlled plunger carried beneath it makes contact with the pin and puts the called subscriber's instrument to line, as subsequently explained. The electrical connections are shown diagrammatically in Fig. 14, where 132, 133 denote the answering and calling plugs of the operator's cord circuit connecting the jacks of the two party lines 448, 766. The circles B, B' represent other r subscribers stations bridged across the same party lines. Associated w i t h each jack at the exchange is a stepby-step device of the same character as that shown in Fig. 1, with the exception that the switch arm 25 normally rests on an insulating-block 143, and moves over a contact ring 144 connected to the calling lamp 146. The subscriber's station on the line 448 may be supposed to be station No. 19, and that on line 766 No. 5. Associated with the cord circuit are the "automatic selector" 81, the operators bead set 135, the clearing-out drop 138 bridging the cord circuit, the ringing generator 137, a ringing key 136 of the ordinary type for ringing through a complete metallic circuit (not used in calling up a subscriber on a party line), a listening key 134, a key 140 for connecting the "automatic selector" to the calling plug 133, a key 141 for sending a reverse current from the battery 142 through the line connected with the plug 133 to restore all the switch arms 25 to the normal positions, and a selective ringing key 139 for calling up a subscriber on a party line. A calling subscriber, say at station No. 19, manipulates his generator 120, which sends intermittent unidirectional currents to line through the connection 155 on the one side, and the contact block 54, switch arm 25, frame 20, and connection 158 on the other. The currents thus sent are in a direction tending to release the switch arm, not to space it forward, consequently all the switch arms on the line either remain in the normal position or, if not already so placed, return to it. The apparatus 29 at the exchange is, however, reversed with respect to the line as long as no plug is inserted in the jack, and its switch arm consequently moves and completes the local circuit of the lamp 146 through the ring 144 and contacts 148, 149. The operator answers the signal thus received by inserting the calling plug 133 in the jack. In Fig. 14 the answering plug 132 is shown inserted in the jack, representing a later stage of the proceedings. By inserting the plug, contact is broken at 149 and the lamp 146 is extinguished, and, at the same time, the connection of the instrument 29 with the line is reversed so that its switch arm is in a position to be spaced forward by currents which actuate the switch arms at the subscribers' stations. The operator then manipulates her listening key 134 and ascertains the number of the subscriber calling and also of the subscriber to be called. The subscribers speaking circuit at this time includes the condenser 122, contact 54, switch arm 25, and conductor 158 on the one side, and the induction coil 123, switch-hook contacts 162, 163, and conductor 155 on the other. The operator inserts a pin in hole No. 19 of the ring 81 (i.e. the number of the calling subscriber), turns the crank handle round to the stop 102, and releases it, first, however, manipulating the key 140 which connects the automatic selector with the calling plug 133. As the crank handle returns to the normal position, a series of intermittent currents is sent to line, and all the electromagnets 29, including those at the exchange itself, are repeatedly energized so as to space forward all the switch arms 25 in synchronism with one another and with the crank handle. At the substation No. 19 the stud 55, Fig. 1, is inserted in the hole 19; consequently at the moment when the switch arms are opposite the holes 19 a circuit is established from the positive pole of the battery 142 through the contact device of the crank handle, the selector pin 83, ring 81 and earth, returning by the electromagnet 65 at substation No. 19, ring 52, stud 55, switch arm 25, line wire 127, and the sleeve side of the cord circuit. The armature is now attracted, and a common contact made between the plates 61, 59, and the catch 73 which locks them together. The telephone at the calling subscribers station is now bridged across the line through the condenser 122, contact plate 59, catch 73, and conductor 158 on the one side, and through the induction coil 123, switch hook contact springs 162, 163, and conductor 155 on the other. At every other sub-station on the line both the ringing circuit of the generator 120 and the speaking circuit are open at the contact block 54, so that neither signalling nor listening is possible. The operator at the central station having thus locked out all the subscribers on the line except the calling subscriber, inserts a selector plug in hole No. 5 of the ring 81, and proceeds to call up subscriber No. 5 on party line 766. This she does by removing the calling plug from the jack of line 448 and inserting it in the jack of line 766. By means of the automatic selector and the key 140, the instrument at substation No. 5 is bridged across the line 766 in the manner described above, and all the other instruments looked out The selective ringing key 139 is then manipulated, the ringing current being sent through the sleeve side of the cord circuit, line 127, conductor 158, catch 73, contact plate 61, spring 69, switch springs 174, 173, bell 119, and earth, returning bv the conductors 173, 179. When the called subscriber removes his instrument from the hook, it is bridged across the party line, and communication between the subscribers is complete through the cord circuit. Ringing off is effected by either of the subscribers manipulating his generator and thus actuating the supervisory drop 138. If the called subscriber is on the same partly line as the calling subscriber both pins may be inserted in the ring 81 and both instruments bridged across the line by a single operation of the crank handle of the automatic selector. Any number of subscriber