Patent GB-190321078-A (GB)
Title: An Improved Party Line Telephone System
Inventor: HEIDE HENRY CONRAD
Filed: 1903-10-01
Granted: 1904-08-04
Abstract: 21,078. Heide, H. C., [Lowry, G. A.]. Oct. 1. Telephone systems; telephone calls.-Relates to party line telephone systems in which all calls are made through the exchange, a central battery being used for calling purposes. The selecting-devices at each instrument for receiving the calls from the exchange are adapted to be set by a definite number of current impulses in one direction, and are restored by a current impulse in the opposite direction. Fig. 1 shows the selective calling-apparatus at the subscribers' stations. The call itself is given by alternating current from a magnet at the exchange, the current traversing the bobbins a and setting the polarized armature band hammer d in vibration. Prior to this, however, it is necessary to rotate the notched disc e into such a position that the notch is beneath the downwardly-curved end of the armature b, which is otherwise locked against movement. The rotation of the disc is effected by means of a definite number of unidirectional currents which are passed through the bobbins a and cause the spring- controlled non-polarized armature f<2> to space forward the ratchet-wheel e<6> by means of a pawl. At all stations on the party line, the shafts e<2> are rotated equally, but it is only at the selected station that movement of the bell hammer is permitted by the notch. The armature f<2> is not attracted when alternating current from the magnets is passing, Pivoted on the other side of the electromagnet is a third armature, which is polarized and serves to disengage a spring - tensioned detent pawl from the ratchet-wheel e<6> when a reverse current is passed through the bobbins a. The shaft e' and disc e then return to the normal position under the control of a spring e<5>. A second discj is provided with two holes adapted to receive a pin h<2> on the switch arm h. One of these holes allows the switch arm to rise when the receiver is lifted from the hook to give the call at the exchange ; the other allows the switch arm to rise when a call is being responded to. At all other stations than the one called by the exchange the switch arm is prevented f:rom rising, and the receiver is consequently locked out from access to the line. A spring hook f<5> on the end of the armature f<2 >serves as a locking-device to prevent movement of the third (polarized) armature while the magneto currents are passing. In the arrangement shown in Fig. 5, two stations are shown on the party line A, B. The selective calling-apparatus described with reference to Fig. 1 is indicated diagrammatically at a. The exchange is called by lifting the receive:r from the hook h and thus making a momentary or passing connection at h<3> between the line A. and earth G<2>. A third metallic conductor may be used instead of the earth connections. The momentary current passes from the battery C to the jack spring m<2> and line B, passing thence to earth through all the selecting-instruments a in parallel, and giving one forward movement to all the discs e, j<1> except those at the calling-station. The other telephone instruments on the line are thus locked out as soon as a call is made by lifting a receiver from its hook. The signal at the exchange is given by means of a momentary current in a circuit in parallel with that just described, and comprising the conductor 3, coil H<4>, line A, and earth. The current in the coil H' causes the switch member H' to close the circuit of the signal lamp H. The exchange operator then inserts the answering-plug n, n<2> in the jack, and after ascertaining the line called for inserts the calling-plug N, N<2> into the corresponding jack. The impulses sent into a line to select the required station may be sent by automatic means, but in the arrangement shown in Fig. 5, they are sent by ordinary table keys. The key o, o<2> is pressed repeatedly to send the current impulses to line through the calling-plug ; the key p, p' sends the ringing current from the magnet M ; and the key r, r', when pressed in conjunction with the listening key s, s' of the cord circuit concerned, sends the reverse or restoring current to both lines. Part of another cord circuit is shown in Fig. 5, a single key r, r<2> serving for all the cord circuits used by one operator. The clearing signal q bridges the cord circuit, and is operated by a momentary current when either receiver is returned to its hook, the circuit comprising the coil H<5>, the tip side of the cord circuit, drop g, sleeve side of the cord circuit, and line A to earth. As. however, current also flows through the coil H<4> and line A direct to earth, the lamp H is not extinguished until the reverse current is sent by pressing the keys s, s' and r, r<2>, when, in addition to the current in the two lines produced by bridging the battery C across the cord circuit, a local current also flows through the coil H<5> and the tip side of the cord circuit to earth. In a modified system, the reverse or restoring current is sent automatically when both receivers are hung up, supervisory drops in the cord circuit being provided with pairs of contacts in series which put the battery in bridge of the cord circuit when both drops are operated. Figs. 7 and 9 show automatic apparatus for transmitting the series of current impulses which operate the selective apparatus. One automatic apparatus is provided for each operator, and by pressing one of the keys p, P, &c it may be associated with the calling plug of any cord circuit in use. When the plunger w bearing the number of the station to be called is depressed, its conical end engages with one of the openings x<2> in a movable disc x<3> and moves the disc sufficiently to cause the pin x to flex the spring u into contact with the spring u<2>. The plunger is detained by its shoulder w<3> until the travelling- arm k reaches it, when the spring u returns to its normal contact with the spring u<3>. A switch arm t<2 >is normally in contact with the block t, and the depression of a plunger consequently closes the following circuit :-Battery C, key p, tip side of line, sabscriber's instrument, sleeve side of line, conductor 20, switch t', contacts u, u' and earth. At the same time a shunt circuit is closed through the key p, conductor 26, and electromagnet y, with the same return through the switch t<2> and contacts u, u<2>. The attraction of the armature y<2> causes the ratchet-wheel k<2> to move through one tooth, carrying the arm k with it. At the same time a balance-wheel y<3> receives an impulse through a depending projection y<5>, causing it to oscillate so as first to remove the switch arm t<2> from the contact block t by means of a pin y<6>, and after a short interval of time to restore it by means of the pin y<8>. The restoration of the switch arm produces another current impulse, and these continue until the arm k strikes the depressed plunger and releases it. The contact between u, u<3> which then follows puts the magnets M to line to give the call, one terminal being connected directly to the tip side of the line through the key p, and the other to the sleeve side through the contacts u<3>, u, switch t<2>, and conductor 20. The depression of the plunger w, followed by that of the key p, thus effects the transmission both of the selective and the ringing currents. To call an individual line, one of the keys p, P, &c. alone need to be pressed, the magneto circuit being normally closed at u, u<3> and t<2>, t. The duration of the current impulses can be varied by inserting the pin y<6> into any selected one of the various holes y<60> provided for it. Reference is made in the Provisional Specification to Specification No. 26,566, A.D. 1901.