Patent GB-246219-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1924-10-22
Abstract: 246,219. Siemens Bros. & Co., Ltd., and Humphries, H. E. Oct. 22, 1924. Automatic and semi-automatic exchange systems. - During the establishment of a connection a relay bridged across the speaking conductors is held energized from battery and earth at each switch seized to control the maintenance of the connection, but if a busy group of trunks is encountered or if the called line is found busy the bridged relay releases, the seized switches subsequent to or including the first group selector are automatically released, and a busy signal is transmitted to the calling party. The system operates in a similar manner if a faulty trunk in which one of the conductors is open is encountered. In one arrangement in which a call is extended over a preliminary selector, Fig. 1, first and second group selector, Figs. 2 and 4, and a final selector, Fig. 5, the bridged relay GA is arranged at a feed bridge at the first group selector, and if a busy condition is encountered the release of relay GA releases the group and final selectors and causes the preliminary selector to advance to its last position in which a busy tone is transmitted to the calling subscriber. Fig. 6 shows a two-wire link to a manual position specially designed to maintain relay GA energized. In a call established by a manual operator, the cord circuit, Fig. 7, is employed, and a busy flash signal as well as a busy tone is given to the operator if a busy condition is reached. In a modified system, the busy tone may be transmitted from the first group selector, in which case only the second and subsequent selectors are released. Preliminary selector, Fig. 1. When a subscriber calls, line relay R is operated over a circuit including wiper E‹ of the preliminary selector and a normal contact thereof, and closes a driving circuit DM, r2, t4, C‹, r1 including a normal contact of the wiper C‹. If the first trunk is busy, magnet DM operates again over the grounded wiper C‹, relay R remaining locked up over wiper E‹ and contact r3. When an idle trunk is reached relay T operates and disconnects relay R. The connections of the line relay R are such that even if, on a busy condition being reached, as described in later paragraphs, the test relay T releases whilst the receiver is still removed from its hook, the relay is unable to energize again until the preliminary selector reaches the last contacts of its bank. First group selector, Fig. 2. Relay A operating over the calling loop completes a circuit over normal contacts k2 for release relay B which earths the incoming test wire to hold up the preliminary selector. Relay B also energizes the polarizing winding of relay SF and lights the alarm lamp PL. The first impulse of the first digit is repeated over the circuit a1, d5, k1, b2 to the vertical magnet VM in series with relay C which operates to energize release-control relav HA and to complete a new circuit a1, d5, k1, b3, c3, over which the remaining impulses of the first digit are repeated. Relay HA disconnects lamp PL and holds relay B operated. At the end of the digit, relay C releases and completes a circuit ha1, d6, c1, for rotary magnet RM which operates and in completing its stroke closes contacts rm1. If the first trunk in the selected level is busy, relay D is short-circuited and relay E operates over contacts rm1, r1, ha5, C', opens the rotary magnet circuit and maintains relay HA energized. Rotation thus goes on under the combined action of magnet RM and relay E until an idle trunk is reached when relay D operates in series with relav E which does not now operate. Relay D switches through to the seized trunk and a bridged relay GA operates over battery and earth at the succeeding switch to maintain relay HA operated. The remaining digits are repeated to succeeding switches at contact a2, relay C operating during each digit over contacts a1, d5. ha3, sf3, to disconnect relays GA, SF so as to improve the impulsing circuit, relay HA being held operated at these times over contact c 2. Second group selector, Fig. 4. Relay A operating in series with relay GA, Fig. 2, energizes release relay B and the impulses of the second digit are repeated at contact a2 to the vertical magnet VM in series with relay C. The relapse of relay C at the end of the digit completes a circuit d5, b2, c1, e1,. k1 for the rotary magnet RM which then interacts with relay E to select an idle trunk in the same manner as described above for the first selector. When an idle final selector is reached, relay D operates and relays A, B release extinguishing the alarm lamp PL. Final selector, Fig. 5. The impulse relay A operates in series with the bridged relay GA, Fig. 2, over a normally-closed contact mm1 of the release magnet. The tens impulses are repeated over contacts a1, h5, b2, f4, g2 to the vertical magnet VM in series with relay C. The relapse of relay C at the end of the digit completes a circuit over rotary off-normal contacts w1 for relay G which operates to place the rotary magnet RM in the impulse circuit. Relay C operates again during the reception of the units impulses and maintains relay G operated over contacts c1, g1 and operated contacts w1. The relapse of relay C at the end of the digit breaks the circuit of relay G which however is slow to release. Relay C also connects test relay H over the circuit b4, k1, w1, g1, c2, H, b3 to the test wiper C' so that if the wanted line is free, relay H operates and short-circuits its high-resistance winding 1 to mark the line busy. Ringing. The subsequent relapse of relay G connects ringing current over winding 1 of relay F to the called line, a ring-back signal being also transmitted to the calling line over contacts mm1, h6, f5 from a lead RS. When the called subscriber replies, relay F operates, removes a short-circuit from its holding winding 2, and connects up reversing relay D which operates in series with the called line. Metering. The reversal of current through polarized relay SF, Fig. 2, causes this relay to operate and transmit an impulse over the circuit sf1, M‹, Z, t1, D‹, r2, DM to the meter Z, Fig. 1, which locks up over contact z1. Release. When the calling subscriber hangs up, relays A, B, SF, Fig. 2, release and open the bridge through relay GA which releases relays HA, D, thus effecting the release of the numerical switches. The removal of earth from wiper C‹ releases relay T, Fig. 1, and a restoring circuit over contacts r2, t1 and wiper D‹ is completed for the preliminary selector. Operation under busy conditions. If the first group selector, Fig. 2, is unable to find an idle outlet, rotation continues until the last contacts are reached when relay D operates as for an idle trunk. The last a and b contacts, however, are left blank so that no circuit is completed for relay GA, and relay HA, which has been maintained operated during the rotary movement by the intermittent operation of relay E. releases and in turn releases relay D. Relay B releases and opens the circuit of relav A which de-energizes and completes the release circuit. The removal of earth from the test conductor releases relay T and completes the restoring circuit for the preliminary selector. When the last contacts of the bank are reached, the line relay R is again connected to the calling line over wiper E‹ and since the calling receiver is off its hook relay R operates to open the driving circuit for relay T which again operates. Relay R is now maintained operated over wipers E‹, A‹, the calling loop. wiper B0 and the winding of a, coil BB which transmits a busy tone to the calling subscriber. When the subscriber hangs up, relays R, T release and the preliminary selector steps to normal. Busy tone is similarly transmitted if the preliminary selector itself fails to find an idle outlet. If the second group selector encounters a busy condition relay GA releases owing to the last contacts of wipers A<2>, B<2> being disconnected, the group selectors are released and a busv tone transmitted from the preliminary selector as before. The last test contacts of the group selectors may be connected to congestion meters CS. If the called subscriber is busy, relay H does not operate but relay F operates nver its winding 2 and contacts b<4>, w<1>, g<1>, and disconnects relay A which releases relay B and closes the release-magnet circuit. The disconnection of relay A also releases relav GA, Fig. 2, and the group selectors are released and a busy tone transmitted from the preliminary selector as before. Call to manual board. Fig. 6. In the case of a call extended from a first or second group selector over a two-wire trunk to the manual board shown in Fig. 6, the circuit for relay GA. Fig. 2, is maintained at first over relay Land later, after plugging in, over battery and earth in the cord circuit, relay L remaining energized for a short interval after the cut-off relay CO operates and maintaining battery and earth connections over contacts l<2>, l<3> until the plug is fully inserted. The cut-off relay is first energized over the tip conductor but maintained energized over the sleeve circuit. Call established by operator. The cord circuit shown in Fig. 7 is employed in conjunction with a first selector similar to that shown in Fig. 2, but modified by the omission of the third and fourth incoming leads c, m and by the insertion of reversing contacts controlled by relay SF in the circuit of relay A. When the answering plug PA is inserted, relays DA, AS operate and the operator communicates with the calling subscriber by throwing her key K to the left. The calling plug PC is then inserted in the jack of an idle trunk and polarized relay SF operates over a circuit through its winding 1, contacts sl4, ha3, ha1, winding 2, contact ha2, and the sleeve of the jack. Relay SF operates to light lamp CSL. The operator then throws key K to the right, thereby completing a circuit for relay HA which removes a