Patent GB-211232-A (GB)
Abstract: 211,232. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. Nov. 17, 1922. Automatic and semi-automatic exchange systems; party-line systems. - The ringing- apparatus of a party-line system is arranged to transmit ringing-current appropriate to the called subscriber in the case of a non-reverting partyline call or a call to a non-party-line subscriber, and ringing currents appropriate to both the calling and the called subscribers in the case of a reverting call. In the latter case, the reply of either subscriber cuts off both currents. The invention is described with reference to a system employing relays only, which is similar to that described in Specification 211.231, and employs an impulse responder, Figs. 3<a>, 3<c>, 3<d>, of the type fully described in Specification 181,119. Each party-line has four stations distinguished by a special station digit, 1, 2, 3 or 4, interposed between the hundreds and tens digits. A calling subscriber wishing to make a reverting call. signals an operator and, after giving his own and the wanted number, hangs up his receiver. The operator then calls a number similar to that of the wanted party but in which the station digit is replaced by one of the digits 5 .... 0, each of which corresponds to a particular combination of the two station digits 1 - - - 4. Thus, subscriber No. 2100 wishes to call subscriber No. 2200 on the same line, the operator dials No. 2600. A station digit 1, - - - 4 causes the energization of one of the relays PYMI, - - - PYM4, Fig. 4, and in parallel therewith a corresponding one of the relays FS1, - - - FS4, Fig. 5, A substituted digit 5 - - - 0 causes the simultaneous energization of two of these relays. The ringing apparatus, Fig. 5, comprises two distributors ED, RD, the former successively grounding leads el - - e4, the latter synchronously connecting up in succession the four partyline ringing-currents. The ringing circuit 31 includes contacts of a relay RGC which is intermittently energized over one or more leads e<1> - - e<4>, according to which of the relays FS1 - - FS4 have been operated. The ringing-circuit is thus only completed at the intervals when the distributor RD is supplying the particular ring- ing current or currents required. Means are provided for preventing a calling subscriber from directly establishing connection with two stations on any other party-line. The system may be modified so that stations having entirely different designation numbers may be connected to the same party line Call to ordinary party-line subscriber (No. 2100). After the complete dialling of the wanted number, the operation of marking relay MC1, Fig. 3<a>, completes circuit 21 for relay PYM1, Fig. 4, in the manner described in Specification 211,231. Relay FS1 is also energized in circuit 2@ in parallel with relay PYM1. The completion of the usual holding circuit 27 energizes relay ITB to complete a circuit 29 for ringing relay RG which connects ringing circuit 31 to the upper talking conductor. Circuit 31 includes contacts of relay RGC which is only energized when lead e1 is grounded. Thus, only the one of the four ringing-currents, which is appropriate to the station digit 1 of the called number, is able to be transmitted over lead 31. Calls to single party-line subscribers may be established in a similar manner by means of an operator, the impulse-responder, Figs. 3<a> - - 3<d>, being taken into use in this case over a relay PO instead of over the relay PF. Reverting call. Upon the dialling of No. 2600 in order to connect subscribers 2100, 2200 as referred to above, relays PY1.6, PY6.c, Fig. 3<c>, are operated, and, upon the energization of marking relay MC1, circuits 21, 37 are completed for relays PYM1, PYM2, and circuits 26, 37<a> for relays FS1, FS2. Relay RGC is now energized over either of the leads e1, e2, and two ringing-currents appropriate to the calling and called subscribers are transmitted alternately. The reply of either subscriber completes circuit 32 in which relay RT energizes and cuts off both ring- ing-currents, the cessation of ringing at the calling subscriber's bell, affording an indication that the called subscriber has replied. In order that subscribers having different hundreds, tens or units digits, for example, subscribers Nos. 2209, 2100, may be accommodated on the same party line and have reverting-call facilities, the relays PYM are provided with change-over contacts as shown in Fig. 4a. The operator would then dial No. 2600 (corresponding to the number having the smaller station digit) and the provision of the change-over contacts prevents the completion of marking-circuit 25<a> corresponding to subscriber 2200 who is on another line. A calling subscriber having access to the impulseresponder, Figs. 3a - - 3d, over relay PF is prevented from calling two stations on any other party-line by the provision of circuit 40 which is completed if a station digit 5 - - 0 is dialled and causes the energization of relay SU which results in the release of the impulse-responder and the transmission of a distinctive tone to the calling- subscriber. Call to non-party-line subscriber. Non-partyline subscribers have 3-digit numbers, the first digit being other than 2 or 3. Upon a call being made to such a number, relays HD2.7, HD3.8 will not be operated unless relay HD6.c is also operated. In any case, circuit 12 for relay DMP will not be completed, no PY relay will be operated and the second digit will be recorded on the TN relays. None of the relays FS1, &c. will be operated and ringing current from the additional lead e<5> will be projected to the called line. Specifications 181,120 and 211,229, the latter of which claims other features of the system which are not claimed herein, are referred to.