Patent GB-498416-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/00
Filed: 1937-07-09
Abstract: 498,416. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and HYDE, G. A. M. July 9, 1937, No. 19112. [Class 40 (iii)] In a teleprinter automatic-exchange system, means is provided whereby, in response to the transmission of a special signal from the substation of either of two parties connected together for communication, an operator can be brought in without disturbing the connection. The signal transmission circuit at the exchange includes a series circuit over contacts of the line relays and windings of signalrepeating relays of both subscribers, the intervention of the operator in response to the receipt of the special signal connecting transmitting contacts of her teleprinter and a relay repeating signals to the teleprinter also into the series circuit. The special signal may be a repetition of the signal normally employed for breaking down a connection. An operator may also intervene in an existing connection to offer a preferred call. In the system described, each subscriber has an individual two-motion selector, the wipers of which are shown at the righthand side of Figs. 3 and 4, whilst the leads incoming at the left-hand side are from contacts individual to this subscriber in the selector banks of other subscribers. The selector may be set by one digit (7, 8, or 9) to select an idle line of a group or by three digits (the first, 3, being absorbed) to select an individual line or a small group of lines. Two parties may be connected to a single line, a call from one party to the other being made by dialling digit 1 or 2, whilst for incoming calls the parties have separate numbers and individual connections to the selector banks. Other features of the system described are claimed in divided Specifications 498,425 and 498,428. Dialling ; P.B.X. hunting. When the dial, Fig. 1, moves off normal, relays DR, DN, ST operate, busy lamp RL is lit, the teleprinter magnet TRM is connected to the contacts of relay LR, and the teleprinter motor M is started by relay MS. Relay DR responds to the impulses repeating them over line L to relay LLR, Fig. 4. At each impulse, the movement of relay LLR to spacing closes a circuit over the middle and right-hand windings of relay TR (which does not respond) and the right-hand winding, of relay SS which repeats the impulses through relay LDR to vertical magnet VM. At the first impulse, relay LST operates, and at the end of the impulse, relay SB energizes STR which locks and lights supervisory lamp SL at the operator's position. When the dial returns to normal, relay DN releases but DR remains locked. If the digit dialled is 7, 8, or 9. relay HS energizes at the end of the digit over vertical bank VB and locks over its lefthand winding in series with the rotary magnet RM. Hunting over the selected group takes place under the interaction of magnet RM and relay E, relay HS remaining held over its right-hand winding and ground on wiper PBXA as long as lines of the group are encountered. When an idle line is reached, relay THR operates over wiper TH. If a first digit 3 is dialled, relay DA operates over vertical bank VB completing a circuit for release magnet ZM, and on return to normal relay OA operates. The second digit is repeated to the vertical magnet and at the end of this digit relay E operates so that the third digit passes to the rotary magnet. If the line selected is the first of a group, the release of relay E at the end of the digit causes relay HS to operate and initiate hunting as before. Called line busy. With relays THR, HS de-energized, relay BB operates from ground periodically applied to lead PU and signals corresponding to the word " busy " from leads BC are repeated by relay TR over the line L to the teleprinter TRM, relay SR being operated by relay SS during the signals to disconnect relay LLR. At the end of the signals, relay TO operates from ground on lead TO to complete a circuit for release magnet ZM. The calling subscriber can then dial another number without releasing the connection. Unobtainable numbers. If a line reached is out of service, its contact in the bank of wiper NU is connected to ground so that relay NU operates. Relay BB operates as before and signals corresponding to the words " number unobtainable " are transmitted from leads NU, the switch being then released as before. If a first digit 1, 2, 4, 5, or 6 is dialled, relay NU operates over vertical bank VB at the end of the digit. Called line idle ; communication. Relay THR energizes in series with relay CD in the called subscriber's circuit and this energizes relays DD, ON, LST, SB, STR. Relay THR operates relays H, ON, and connects relays TR, SS of the calling circuit over wipers RC, TR to the similar relays of the called party's circuit. In the latter, relay AB operates from lead PU to connect up lead CS which supplies a 70- millisecond spacing signal followed by a 1¢ second marking signal and then by the " who are you ? " signal. These are repeated by relay TR to the called substation at which relays LR, SSR respond. At the spacing signal, relay SA operates, and at the marking signal, relays SBR, ST, MS operate, lighting busy and incoming call lamps RL, GL, and preparing the teleprinter to receive the " who are you ? " signal. This signal causes the " answer back " signal to be sent out at contacts TTC, and this is repeated by called party's relay LLR to calling party's relays TR, SS and thence to the calling line. At the end of the signals from leads CS, relay TO operates to release relay AB and communication may then take place, all signals being repeated over the circuit including relays TR, SS of both subscribers, but the circuits being such that, for the sending subscriber, the middle and right-hand windings of these relays have current in opposite directions during spacing and therefore do not respond, but, for the receiving subscriber, the middle windings are disconnected and the relays therefore respond to the spacing signals in the right-hand windings. At the receiving party's circuit, relay LLR is short-circuited by relay LG during and for a short period after signalling to prevent false signals due to discharge of the line through the relay. Release. If either party operates his release key RK for at least one second, relay RR operates and spacing current is applied to line L and relay LR. Relay SSR operates relay SA and disconnects SBR which on release operates relay WR. When the key RK is restored, relay SBR re-operates energizing XR, and on the relapse of relay SA, relay SCL operates to release ST and all operated apparatus. At the exchange circuit of the party operating the release key, relays SS, SR, LG operate and on the release of SB, relay W operates. At the restoration of key RK, relay LLR operates to marking position, relay SB re-operates and energizes X, and relays SR, LG release so that negative battery is applied to the left-hand winding of relay CL in the circuits of both parties. Both relays operate, energizing relays CLR which release STR and all operated relays, and in addition a circuit is completed for the release magnet ZM of the operated switch. The release signal is also repeated to the other station to effect release there in a similar manner. Forced release. If one of the parties receives no signals for a certain time, relays ZA, ZB in his exchange circuit are successively operated by timed pulses to change over the connections to relay CL so that positive battery is applied to both windings (through the right-hand winding from ground over back contact zb3 in the other exchange circuit), but, the currents in the windings being opposed, the relay does not operate. When relays ZB in both exchange circuits have operated, no circuits exist for the right-hand windings of relays CL so that both operate and release the connection. Party-line working. The circuits shown in Fig. 2 are added to the substation circuit and contact sa1 is disconnected from relay SBR and connected to relay SRR. In addition the circuits of the teleprinter motor and magnet include one or other of the dotted connections shown. The two stations are denoted by digits 1 and 2. Assuming that the station shown calls the other station by dialling digit 2, relays LR, SSR of the called party repeat the impulses, relays SA, SRR being operated during dialling. Relays O, PA, SE, PB successively energize under the spacing and marking conditions of the two impulses. On the relapse of SA, relay ST operates to start the motor M over contacts pa9, pb8 and connect up the teleprinter magnet over contacts pa7, pb6. At the calling station, contacts dn5 operate relay PA to energize relay MS and lock PA. Similarly, when station 2 calls station 1 by digit 1, relay PA only is operated. The exchange apparatus is released in response to digit 1 or 2 as already described. When a digit greater than 2 is dialled, i.e. for an external connection, both relays PA and PB are operated at the non- calling station so that its teleprinter is not started, but that at the calling station is started by the operation of relay PA or PB by contacts dn5. At the non-calling station, relays PA, PB are released at the end of the digit, but ST remains operated to light busy lamps RL, GL. For incoming calls, the two parties are connected to leads TH1, TH2. For a call to party 1, the spacing and marking signals preceding the "who are you?" signal provide the single impulse necessary to select party 1. For a call to party 2, relay PD operates over lead TH2, energizes relay CD and marks lead TH1 busy, and changes over from leads CS to CTP so that the " who are you ? " signal is preceded by two selecting impulses. Calling an operator. If digit O is dialled, relay RC operates over vertical bank VB, flashes lamp CAL, and energizes release magnet ZM. The operator throws key PK1 . . . 3 operating relays OP, ON. Relay OP locks in series with relay MN which prevents more than one relay OP being opera