Patent GB-190412187-A (GB)
Title: Improvements in and connected with Telephone and Telegraph Systems.
Inventor: RITTER GEORGE
Filed: 1904-05-28
Granted: 1904-08-25
Abstract: 12,187. Ritter, G. May 28. Telephone systems; telegraphs; telegraph and telephone calls.-On a party line, three or four line-wires are used, one of which, designated 3 in Fig. 6, contains in series an electromagnet m<3> in each subscriber's apparatus, and is used only for opening a switch u<3> to disconnect his instruments from the line-wires. The invention is described for telephony, but may be used for telegraphy. In the arrangement shown, three line-wires 1, 2, 3 are used, with earth connections e<3>. The wires 1, 2 are for calling and speaking only. The extreme ends of the wire 3 are connected to like terminals of two equal batteries (not shown), the other terminals of these being earthed. Fig. 6 shows one subscriber's apparatus, including the electromagnet m<3>, a hand-switch t<3>, a latch k<3> for it, a receiver f<3>, hook lever h<3> operating contact-springs d<1>, d<2>, d<3>, an induction coil with primary p<3> and secondary s<3>, a local battery b<3>, a transmitter c<3>, and a call bell g<3> and generator i<3>. The call bells of different subscribers may be connected to either wire 1, 2, and operated by current in either direction, four separate calls being thus possible. When the receiver f<3> is removed from the hook lever h<3>, the springs d<1>, d<2> close the receiver circuit f<3>, s<3>, and the transmitter circuit b<3>, p<3>, c<3>; the spring d<3> connects the middle of the electromagnet coil m<3> through switches t<3>, u<3> to earth e<3>. The two halves of the coil m<3> then carry equal and opposite currents from the two batteries to earth, and the electromagnet m<3> thus remains inactive, while all other electromagnets in the line 3 attract the triple switches u<3> against spring pressure, and so disconnect the telephones. The switches u<3> may have indicators showing when the line is occupied. If the subscriber wishes to communicate with another on the same wires 1, 2, 3, be removes his receiver f<3>, informs the exchange, and replaces the receiver on the hook lever h<3>. The exchange calls the second subscriber, who removes his receiver and presses his switch t<3>, which disconnects his electromagnet m<3> from earth, so as to free all the switches u<3> on the wires ; the switch t<3> also presses together twc springs n, o, shortcircuiting the electromagnet m<3> through the switch u<3>. The switch t<3> is then held down by the latch k<3>, this being pressed forwards by the raised hooklover h<3>. When the calling subscriber sees that his switch u<3> has been freed, he removes his receiver, and thus disconnects all the subscribers' apparatus except that of the second subscriber, whose electromagnet m<3> has been rendered inactive by the depression of the switch t<3>. After the switch u<3> in any subscriber's apparatus is opened, depression of his key t<3> does not short-circuit the electromagnet m<3>, so that he cannot connect his telephone to the wires 1, 2. When the receivers are replaced. on the hook levers, all the switches u<3> are released. Instead of using the switch u<3> to prevent electrically, the short-circuiting of the electromagnet m<3>, the switch u<3> may be placed so as mechanically to prevent depression of the hand-switch t<3>. The switch u<3> may short-circuit the receiver f instead of disconnecting it from the line-wire 1 ; to reduce the effect of the short-circuit thus produced between the wires 1, 2, a resistance is placed in series with the receiver. When the switch u<3> is in its normal position, it short-circuits this resistance. The electromagnet m<3> may be used without the middle connection, and the springs n, o dispensed with, an additional contact being touched by a spring moved by the rise of the hook lever, to connect both ends of the electromagnet coil to earth, in order to operate all other electromagnets in the wire 3. With this arrangement at a terminal station, the short circuit of the electromagnet also short-circuits the battery there, in the wire 3 ; to reduce the current produced, the electromagnet at the terminal station is wound differentially, one coil being included as a resistance in the short circuit. In this arrangement, the switch u<3> may be placed so as mechanically to prevent rise of the book lever h<3> while the switch u<3> is open. The local battery b<3> may be dispensed with by connecting the primary winding p<3> and the transmitter c<3> in series, or preferably in parallel, both being in series with the electromagnet m<3>. Instead of using two batteries at the ends of the wire 3, these ends may be connected by a line-wire to one terminal of a single battery, the other terminal of this being connected to earth or a return wire ; one of these wires may be one of the calling and speaking wires 1, 2.