Patent GB-770232-A (GB)
Abstract: 770,232. Semi-automatic exchange systems. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Dec. 21, 1954 [Dec. 24, 1953], No. 36908/54. Class 40 (4). At a P.B.X. where main exchange lines (conveniently termed junctions) terminate in line circuits which can be connected to P.B.X. subscribers under the control of an operator, conditions requiring the attention of the operator are indicated by a set of lamps common to all the line circuits. Thus the lighting of a lamp indicates that at least one line circuit is in a particular condition, and actuation of a corresponding one of a set of keys causes a rotary switch to connect the operator's set to a line circuit in that condition. The following conditions result in the operation in a line circuit of the relays named:- junction held and waiting (W), called P.B.X. subscriber free but has not answered within 20 sec. (C), called P.B.X. subscriber busy and has not cleared down local call within 20 sec. (D), P.B.X. subscriber recalls operator (F), P.B.X. subscriber transfers call to operator (T), incoming call to several P.B.X. subscribers in succession to be transferred (S), incoming call waiting more than 20 sec. (Y), incoming call waiting less than 20 sec. (H). Relays W, C, &c. control corresponding position relays WR, CR, &c. and these in turn control lamps WL, CL, &c. Relays YR, HR, however, control the same lamp HL which merely lights when HR comes up but flashes when YR also comes up. Relays W, C, &c. also prepare markings for the switch BK which serves to connect the operator's set TF, and these markings are completed by one of position relays WB, CB, &c. energized when an appropriate key WT, CT, &c. is actuated, the switch being started by relay GB. The switch BK may be marked by different electrical conditions instead of by separate marking wires. Incoming calls.. Relay A responds to ringing current and connects up H, HR, lighting lamp HL and general signal lamp AL. After 20 sec. Y, YR pull up. By actuating key HT the operator causes the switch BK to connect her set to the junction to learn the caller's requirements, B, Z being operated, after which by means of key ST she energizes BD to connect to the internal side of the junction line circuit, the junction being held and the finder OZ being started, and sets up the wanted connection by dialling. If the wanted subscriber is free, P energizes and connects up ringing current. Upon reply V energizes followed by VV which trips the ringing and reconnects the operator's set. The operator retires by actuating key ET (or any other key), when B, BD release and the connection is switched through. When the P.B.X. subscriber hangs up, V energizes momentarily to release the internal connection. The operator may release a connection by means of key UST. If the wanted subscriber is busy, the operator receives busy tone and she may reconnect to the incoming junction by actuating key UT. If the operator is unable to complete the wanted connection at once, the actuation of a key to deal with another call results in the operation of W, WR, the junction is held and lamp WL lights. Reconnection to the junction is effected by means of key WT. If the operator retires immediately after dialling, the non-reply of the wanted subscriber is indicated by lamps CL, DL, and she can reconnect to the junction to inform the caller. The P.B.X. subscriber can recall the operator by actuating for at least 3 sec. a key which earths the a wire and thus energizes differential relay X. This leads to the operation of F, FR and lighting of lamp FL. By throwing key FT, the operator connects to the internal side of the junction line circuit. If the subscriber hangs up after actuating his key, the internal connection is released, T, TR operate and lamp IL lights. Key TT effects connection to the incoming junction. If the subscriber actuates his key for a shorter period than 3 sec. he becomes connected by relay Q to line RL, over which he may set up an internal call, the junction call being re-established by a further key-actuation. If an incoming call is to be extended to several P.B.X. subscribers in turn, the operator actuates key SIT to operate SE before setting up the first connection. As a result release by the P.B.X. subscriber energizes S, SR, holding the junction and lighting lamp SL, and the operator then actuates key ST and sets up the next connection. Relay SE is finally released by key SUT. Outgoing calls. The P.B.X. subscriber obtains access to a trunk wired to the switch BK and a calling lamp lights. The operator connects to the trunk as described above. If there is a free junction, she connects thereto by actuating key BT and sets up the required call by dialling. A fresh connection is made to the P.B.X. subscriber in the same way as for an incoming call. Lamp BL-lights if all junctions are busy. Blind operator. Switch NT is closed to operate relay N. Relays CR, DR, &c. are now such that only one can operate at a time, preference being given to the most important conditions. These relays also control the connection of characteristic signals, e.g. of different frequency, from sources LC, LD, &c. to a sound-reproducer GW. Relay WR controls a signal from source LW which may be superposed on any of the other signals. Keys CT, DT, &c. are connected in parallel and if desired a single key MT may be used instead. To discover whether there is a free junction, the operator throws key LBT and hears a tone if BR is up. Several operators. In a modification, Fig. 3 (not shown), each junction line circuit contains an extra relay for each operator's position to ensure that once an incoming call has been answered the signals controlled by relays W, C, D, S are given only to the answering operator. It is arranged also that only one switch BK can operate at a time.