Patent GB-190610598-A (GB)
Title: Improvements relating to Telephonic Exchange Systems
Filed: 1906-05-05
Granted: 1907-05-04
Abstract: 10,598. Lake, H. H., [Stromberg-Carlson Telephone Mannfacturing Co.]. May 5. Telephone systems ; telephone calls.-In junctionline working, means are provided for connecting the subscribers connected with a sub-exchange with subscribers on the main exchange, the main feature of the invention being the improved supervisory arrangements. The final application of ringing-current to the called line is delayed until the operator at the sub-exchange has made the proper connexions with the junction line, this control being entirely automatic. The invention is described as applied to a system in which the called subscriber is on a party-line, a selective call being obtained by the use of currents of different frequencies. The selective ringing-mechanism for the main exchange is similar to that described in Specification No. 10,600, A.D. 1906, in which a depressed ringing-key is automatically locked in its depressed position, and the ringing-current automatically maintained in connexion with the called line, until the subscriber answers. The ringing- current is periodically interrupted, and other interrupter means are associated with the ringing- relay in the cord circuit, whereby the called line will be grounded for a short interval immediately after each periodical application of ringing-current, thus preventing any damage to the cord circuit apparatus due to the capacity discharges of the line and sub-station apparatus after each disconnexion of the ringing-current. One winding of the supervisory relay associated with the calling side of the sub-exchange cord circuit is included in a circuit which passes to the main exchange and there includes a low or a high resistance relay according as the called subscriber has or has not answered, so that this winding of the supervisory relay is de-energized before the called subscriber replies, and after he has bung up his receiver, thus lighting the supervisory lamp. Fig. 1 shows the calling subscriber at A on the sub-exchange C, connected to the party-line subscriber at P' on the main exchange M. The supervisory relays 21, 25 of the sub-exchange have two windings 29, 22, and two armatures as shown, and when both windings are energized the contact 22 is open, but when the winding 20. only is energized, the contact 22 completes the circuit of the supervisory lamp 23. In response to the call lamp 9, the operator at C inserts the answering-plug 13, energizing both windings of the supervisory relay 21 and also the cut-off relay 10. Having ascertained the number of the subscriber wanted, the operator at C depresses the order key 77, thus energizing the relay 78 at the main exchange, and lighting the order lamp 80. The operator at M, by means of the telephone set T, then learns from the operator at C the connexion desired, and at the same time indicates which junction circuit is to be used. The calling-plug 29 is then inserted in the jack 73 of the wanted subscriber, and energizes the cutoff relay 10' and also the relay 38, thereby closing circuits through the supervisory lamp 42, and the lamp 59. The lighting of the latter lamp indicates that the operator at C has not yet inserted the calling-plug 14 in the jack 28 of the junction line. The operator at M then depresses one of the selective ringing-keys 48,completing a circuit from the battery E through the wire 91, relay 57, key 48, wire 92, contacts 93, 94 of relay 46, wires 125, 85. contacts 86, 87, and wire 88 to the battery. The relay 57 locks the depressed key as in the above-mentioned Specification, and at the same time closes the contact 61, thus periodically earthing the battery E through the wire 91, relay 60, wire 96, and interrupter 53. The relay contacts 62, 63, connected to the terminals of the ringing- circuit, are thus periodically connected to the contacts 97, 98, but the ringing-current circuit is incomplete until the relay 58 is energized by the operator at C inserting the calling-plug in the jack of the junction line. The insertion of this plug closes a circuit from the battery S, through the wire 104, winding 25, operator's key 19, jack 28, junction line, winding 33 of the repeating-coil 31, wire 106, contacts 107, 108, relay 45, wire 109, winding 32, tip of plug 14, and winding 26, to the battery. The resistance of the relay 45 is too high to allow the winding 26 to be energized, so that the supervisory lamp 27 remains lighted. The relay 45 is itself energized, and completes the circuit of relay 58 through the contacts 118, 119. The energizing of relay 58 extinguishes lamp 59, but completes the circuit of the ringing-current, which flows from the generator 49, through the interrupter segment 52, key 48, wire 64, contacts 100, 101, wire 102, contacts 63, 72, contacts 70, 69, tip of plug 29, sub-station bell, sleeve strand 40, contacts 97, 62, and wire 103 to the generator. The periodic application of ringing-current is continued until the called subscriber removes his receiver, completing a circuit from battery E through the wire 81, relay 38, plug sleeve, substation apparatus, tip strand 68, contacts 69, 70, contacts 72, 71 (when the relay 60 is de-energized, i.e. when the interrupter 53 is not grounded), wire 121, relay 46, and wire 121 to the battery. The energizing of relay 46 produces several results :- (1) The opening of contacts 93, 94 breaks the circuit of the locking-relay 57, thus releasing the depressed key 48, and permanently breaking the circuit of relay 60 at the contact 61. (2) The closing of contacts 94, 124 completes the circuit of relay 41, thus extinguishing the supervisory lamp 42. (3) The opening of contacts 107, 108, and the closing of contacts 107, 128 substitutes the low-resistance relay 47 for the highresistance relay 45 in the circuit from the subexchange, passing through the winding 26 and repeating-coil windings 32, 33 as explained above. The consequent reduction of resistance in this circuit allows the winding 26 to attract its armature, extinguishing the supervisory lamp 27, so that the operator at C is informed that the called subscriber has replied. When the called subscriber hangs up his receiver, the relay 46 is again deenergized, so that the lamp 42 lights up, and the high resistance relay 45 is substituted for the relay 47, thus reducing the current flowing through the winding 26, and closing the circuit of the lamp 27. If the calling-subscriber's supervisory lamp 23 is also lighted, the operator at C withdraws the plugs 13, 14, breaking the circuit through the relay 45, and consequently of the relay 58 also, whereupon the disconnect' lamp 59 lights up. The operator at M then withdraws the calling-plug 29, and all the apparatus returns to its normal position. A contact 132 on the relay 58 serves to light up the lamp 59 when the plug 14 has been inserted but not the calling plug 29. An additional contact 134 on the relay 41 may be provided in order to maintain this relay energized, and the lamp 42 extinguished, until the operator C removes the plug 14. Otherwise this lamp 42 would light up as soon as the called subscriber hangs up his receiver.