Patent GB-219456-A (GB)
Abstract: 219,456. Coventry Automatic Telephones, Ltd., (Arter, R. C.). June 11, 1923. Automatic and semi-automatic exchange systems.-The subscribers' lines in a small private branch exchange of the relay type are divided into groups, not on the decimal principle, but so that the number of groups is substantially equal to the number of lines in a group. For example, in the system shown, a P.B.X. of 25 lines is divided into 5 groups of 5 lines each. Connections are established over group and units connecting-redays 51, 61, Fig. 1, multipled to intermediate connecting-circuits in a similar manner to the usual tens and units relays in a decimal system, the selection of the particular group and units relays corresponding to a wanted line B, being performed by a single relay counting-chain 30 - - 40. The successive association of the group and units relays with the counting-chain is effected by a single control relay 10, the back contacts of which lead to the group relays, and the front contacts to the units relays. In a larger system, two or more relays such as 10 may be used in parallel. The non-numerical arrangements for connecting a calling line to an idle connecting-circuit also comprise group and units relays 11, 21, arranged non-decimally. Calls to the main exchange may be established automatically by dialling a particular digit combination 24 which extends the connection over conductors 70 - - 72 and thence by means of a set of trunkselecting relays, shown on the left of Fig. 2, to an idle outgoing trunk 85. Alternatively, outgoing trunk connections may be established by a P.B.X. operator C who is wired as an ordinary subscriber, and re-calls the originating subscriber when the desired connection has been obtained. Incoming main-exchange connections are completed by the operator by means of an impulse dial. In the drawing, the conductors marked K - - N, Fig. 1, are continued where indicated by the same reference in Fig. 2. Local call; connection to idle connecting-circuit. The operation of the line relay 1 of subscriber A completes the starting-circuit in which relay 4, associated with the first idle connecting- circuit, energizes and closes circuits for group and units connecting-relays 11, 21. Relay 5 energizes over the calling loop and operates relay 3, which extends the starting-circuit to relay 4<1> of the next idle connecting-circuit, and directly grounds the test wire. The cut-off relay 2 operates quickly over this direct ground, and by disconnecting the line relay opens the starting-circuit before the relatively-slow relay 4<1> has had time to energize. This arrangement avoids the use of an additional slow-release relay to hold open the starting-circuit for a definite time interval. Group selection. The operation of relay 3 also closes a circuit over its grounded middle armature. back contacts of relays 8, 9, and the lefthand armature of relay 5 to operate relay 30. Assuming that the wanted line B is No. 14, the de-energization of relay 5 in response to the first impulse completes a circuit over its left-hand armature for counting-relay 31, and its subsequent re-energization operates relay 32 which releases relay 30. Relay 6 in series with relay 3 is made slow to energize and is shunted by a resistance so that it remains de-energized during an impulse train. In the present case at the end of the single impulse of the first digit, relay 6 energizes and completes a circuit over back contacts of relay 10 for No. 1 group relay 51. Relay 9, energizing over contacts of relay 51, unlocks relays 31, 32 to restore the counting-chain to normal, and operates relay 41 which locks up over contacts of relays 45, 3. Relay 41 opens the circuit of relay 9 which, on the de-energizing, closes the circuit of relay 30 as before, and also operates control relay 10. Units selection. At the end of the second train of four impulses, counting-relays 37, 38 are locked up in a similar manner, and the energization of relay 6 completes a circuit over front contacts of relay 10 for units connecting-relay 61. Ringing. If the wanted line is idle, marginal test relay 8 energizes in series with the cut-off relay 2b, unlocks the counting-chain, prepares a circuit for ringing-relay 46, and completes a circuit for relay 49. Relay 47, energized by relay 49, opens the circuit of the latter which is provided with a vibratory armature and maintains slow-release relays 47, 48 energized for a short interval. During this interval, ringing-current is transmitted to the wanted line over contacts of the ringing-relay 46. At the end of the ringing interval, relay 47 falls back and a silent interval is observed until relay 48 also falls back, when the circuit of relay 49 is re-closed and the whole cycle of operations repeated. When the called subscribed replies, relay 45 energizes and disconnects ringing relay 46. Release. Since all the connecting-relays 11, 21, 51, 61 axe locked over the upper contacts of relay 3, the whole connection is released by the de-energization of relay 5 when the calling subscriber hangs up. Wanted line busy. In this case, relay 8 does not energize and busy tone, generated by relay 42 and characteristically broken up by relays 43, 44, is transmitted over the upper contacts of relay 61 and the upper line contacts of relays 8, 46 to the calling subscriber. Outging call to main exchange established automatically. The operation of connecting relays 52, 61 in response to the number 24 takes place in the manner already described, and the connection is extended over conductors 70 - - 72. Relays 8, 74 energize in series, the latter completing a circuit for control relay 75 associated with the first idle trunk 85. Relay 75 operates trunk-connecting relay 79, and relays 73, 80 then energize in series with relay 8, relay 80 operating relay 76 which extends the starting-circuit to relay 75<1> associated with the next trunk. Relay 80 also locks up relay 79 and bridges relay 82' across the trunk. Relay 45 energizing in series with relay 82 prevents ringing, whilst relay 82 completes a further bridge across the outgoing end of the trunk which causes the lighting of the call lamp 89 at the main exchange, where the call is completed in known manner. The latter bridge includes relay 83 which lights busy lamp 84. When the calling subscriber hangs up, relays 5, 3, 11, 21, 52, 61 are released as before. The release of relay 80 unlocks relay 79, de-energizes relay 76 to free the trunk 85, and disconnects relay 82, so extinguishing lamp 84. Outgoing call established manually. The operator C is called over conductors 100. 101 and bell 97 in the same manner as an ordinary P.B.X. subscriber. The operation of key 96 bridges her head set across the line and on learning that a main-exchange connection, is required, the depression of a key 93, corresponding to an idle trunk 85, bridges the operator's set across the trunk and the removal of the receiver initiates a call at the main exchange by lighting the call lamp 89. The original calling subscriber is recalled in a manner similar to that described below for an incoming call. Incoming call from main exchange. Ringing- current transmitted over the trunk 85 rings the operator's bell 98 and by operating key 93 the operator learns the P.B.X. number wanted, the left-hand contacts of key 93 causing the operation of relay 80 to mark the trunk 85 busy. The operator then throws holding key 95 to operate relay 83 and lamp 84, restores key 93 and operates key 94 which bridges her set across the inner end of the trunk. Relays 81, 80 act as line and cut-off relays respectively, and a connection to an idle connecting-circuit takes place over conductors K - - M in the same wav as a call from subscriber A. The operator dials the wanted P.B.X. number and the connection is completed as before. Upon the reply of the called subscriber, relay 45 energizes and completes a circuit over contacts of relay 12 for a relay 7 which places the release of the connection under the control of the called subscriber. The lighting of lamp 86 over conductor N informs the operator of the called subscriber's reply, and keys 94, 95 are then restored to normal. Modified trunking arrangements to main exchange. If only one trunk is provided, relays 73 - - 76, 79 are eliminated and relay 80 acts as an ordinary cut-off relay. Extra trunks may be added by duplicating this arrangement, each of the trunks having a different number so that a subscriber finding one trunk busy would hang up and call another number. Specifications 185,722 and 193,307 are referred to.