Patent GB-205861-A (GB)
Abstract: 205,861. Relay Automatic Telephone Co., Ltd., and Edwards, W. D. July 20, 1922. Automatic and semi-automatic exchange systems.-In a small automatic private branch exchange in which the transmission of the impulses for establishing a local connection may be performed either by the calling subscriber or by an operator, and in which the operator's services may be obtained by dialling a particular first digit, the insertion of one plug of an operator's cord circuit connects the operator to the calling subscriber and releases the connecting apparatus which has been employed, whilst the insertion of the other plug connects the operator to the connecting- apparatus which is thereby prepared for the reception of further impulses transmitted from the operator's dial. The arrangement is such that the operator, after having obtained a wanted connection, may, when the called subscriber replies, either maintain the connection through her apparatus in which case she has control of the release of the connection, or she may completely disconnect all her apparatus without disturbing the connection, the release being then under the control of the subscribers themselves. The invention is described with reference to an exchange for 100 subscribers in which the connections are established entirely by relays. A calling subscriber C, Fig. 1, is connected to an outgoing trunk OT leading to the connecting-circuit shown in Fig. 2 which selects and prepares an idle impulse-responding device, Fig. 5. The impulse responder operates in response to the two digits of the wanted number to close marking circuits to the wanted line W, Fig. 4, which is then connected to the connecting-circuit, Fig. 2, over an incoming trunk IT1, Fig. 3, the impulse-responder being released. Apparatus arranged for control by an operator is inserted in the outgoing trunk OT as shown in Fig. 1<a> which should be arranged between Figs. 1 and 2. When the operator is not employed, leads A, T, H, B extend directly through the apparatus. In order to attract the operator's attention, the calling subscriber dials the single digit 6, in response to which marking circuits are closed which result in the lighting of lamp CL. The operator inserts the plug AP of her cord-circuit, Fig. 1<b>, into jack AJ, putting herself into communication with the calling subscriber whilst the connecting-circuit, Fig. 2, and the impulse-responder are released. On the insertion of plug CP into jack CJ the connecting-circuit again operates to select an idle impulse-responder which is then controlled by the operator's impulse sender to select and mark the wanted line. Calls to other exchanges are also established by the operator through her cordcircuit, Fig. 1<b>. Call established by subscriber; connection to idle impulse-responder. When subscriber C removes his receiver, his line relay LE energizes a relay OTT which completes a circuit for relays LM, OTC over the test wire T and relay BBM of the first idle outgoing trunk OT. Relay LM energizes relay LC, and relays LC, OTC connect the subscriber's line through an intermediate link LK to the trunk OT and close a holding circuit H for themselves in which the cut-off relay CO operates. Impulse relay A, Fig. 2, operating in series with the substation C, energizes a slow-release relay G which applies a holding-ground to the circuit H, and completes a holding-circuit for relay BBM in series with relay RP. Relay RP closes a circuit for relay RC1 over the test wire TR of an idle impulse-responder, Fig. 5, in series with which relay P energizes and connects battery a to the heavy conductors i, g whereby relays U1.6 - - U5.0 energize in circuits 2, relay RG energizes in circuit 4, whilst relay I1.6 energizes in circuit 3 and disconnects relay U1.6. At this time, the test circuit TR remains unbroken so that the impulse-responder shown is also available to any other calling trunk and is not exclusively associated with a particular calling trunk until the first dialling impulse arrives. The de-energization of relay A at the first impulse energizes relay FI which locks up over circuit 5 in which relay BY energizes and disconnects the test circuit TR to mark the impulse responder busy, locks up relay P and opens circuit 3. Relay I1.6 remains energized over circuit 7 in which relay IH operates and transfers the circuit of relay RG to the impulse wire IR. The re-energization of relay A at the end of the impulse, de-energizes relay RP and succeeding impulses are transmitted to the impulse-responder as intermittent groundings of the wire IR. Selection of wanted line. It will be assumed that calling subscriber C requires connection with subscriber No. 93. When the second impulse of the first digit is transmitted over wire IR, relay I 2.7 energizes over circuit 8 and, at the end of the impulse, relay U2.7 de-energizes and unlocks relay I1.6 whilst relay U1.6 re-energizes over circuit 2. Succeeding impulses act in a similar manner and at the end of the fifth impulse, relay I5.0 is operated and relay U5.0 de-energized. At the sixth impulse relay I1.6 energizes again and, before relay U5.0 has re-energized, relay TN6.c is energized in circuit 10 and locks up. At the end of the ninth impulse slow-release relay RG which has remained energized throughout the digit, falls back and completes circuit 13 in which relay TN4.9 energizes and locks up in circuit 14 in which circuit relay TNH also energizes. Relay TN4.9 unlocks relay I4.9 and de-energizes relay IH; relay U4.9 de-energizes, relay RG energizes and the impulse-responder is ready for the second digit. The first impulse locks up relay I1.6 in circuit 15 in which relay IH again operates to connect relay RG to the impulse wire IR. The second and third impulses operate as before so that, at the end of the third impulse, relay I3.8 is operated, whilst, shortly afterwards, the relapse of relay RG completes circuit 16 for relay MC, the circuit of which includes contacts x of similar relays in other responders to prevent more than one relay MC from being energized at the same time. Relay MC (1) completes circuit 17 for relay HF, corresponding to the 50 lines having a first digit 6 - - 0, (2) completes circuit 18 for relay ITT, Fig. 4, corresponding to the group of 5 lines 91 - - 95, (3) prepares a circuit 19 individual to the wanted line and (4) closes circuit 20 for relay OTM and ringing relay RGX, Fig. 2. Relay ITT opens the circuit S to prevent interference from any other line calling in the same 5-line group, and connects relays ITC, LM to the test wire T1. Relays ITC, LM energize over the test wire T1 of the first idle incoming trunk IT1, Fig. 3, in series with relay OT/IT which connects the trunk IT1 to the outgoing trunk OT. Relay LM completes the circuit 19 in which relay LC energizes and completes the connection over intermediate link LK. Relay OT/IT completes a holding circuit for itself and for relays BBM, F1, ITB (which marks the trunk IT1 busy by opening the test circuit T1), ITC and LC in series with the cut-off relay CO. Release of impulse-responder. The operation of relay MC opens the circuit of slow-release relay P which, after an interval sufficient for effective marking, falls back and disconnects battery from conductors g, i whereupon the marking relays release and the responder is restored to normal. After a further interval, sufficient to ensure complete release, relay BY falls back, rendering the responder free for further service. Ringing arrangements. Ringing relay RGX, energized by relay MC, applies ringing current to the called line in series with relay RT. When the called subscriber replies, relay RT operates, disconnecting relay RGX which de-energizes and completes a circuit for feed-relay B which energizes in series with the called line and completes the talking connection. Release. If the calling subscriber hangs up first, the release of relays A, G opens holding circuits H, HW. If the called subscriber hangs up first, the release of relay B completes a circuit through thermostat T, whereby a battery connection to circuit H short-circuits relays LC, OTC, Fig. 1, which de-energize and release the calling line, the release of relay A opening holding circuits H, HW. Busy test and release. If the wanted line is busy, no circuit is completed over holding wire HW so that relay BBM releases and completes a circuit for relay BB which connects a busy tone from circuit 24 to the calling subscriber and deenergizes relay RGX. Should the calling-subscriber fail to hang up promptly, the thermostat T initiates the release of the connection as in the previous paragraph. Connection established by operator. At the conclusion of the dialling of a first digit 6, relays I1.6, TN6.C are energized and, upon the release of relay RG, relay TN1.6 energizes in circuit 13<a>, locks up in circuit 20<1> in series with relay TNH but does not release relays I1.6, IH since the left-hand contacts of relay TN1.6 are short-circuited at contacts p of relay TN6.C. Relay TNH energizes and completes circuit 16 for relay MC which energizes relay HF and completes marking circuit 18<a> for relay OM, Fig. 1<a>. Relay CR energizes in circuit 20<a>, locks up and lights calling lamp CL. The operator inserts answering plug AP into jack AJ, causing the energization of relay AS which extinguishes lamp CL, directly grounds holding wire H and opens test circuit T to continue the busy mark on the trunk OT. Relay AO energizes in series with the calling line, but relay A is now disconnected and the connecting-circuit, Fig. 2, is restored to normal. If a local automatic connection is required, plug CP is inserted into jack CJ, relay CS energizes and locks up, whilst relay A re-energizes and initiates the selection of an idle impulse-responder as before. The operator throws key K and operates her impulse sender, which controls the impulseresponder to establish the wanted conn