Patent GB-564893-A (GB)
Title: Improvements in or relating to telegraph systems
IPC: H04L12/40
Filed: 1942-08-25
Abstract: 564,893. Telegraph systems ; type-printing telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Aug. 25, 1942, No. 11931. Convention date, Aug. 28, 1941. [Class 40 (iii] In a telegraph system having a number of stations, each comprising a transmitter and a receiver, interconnected by a single two-way trans - mission path, each station comprises means (e.g. a condenser-resistance combination) which initiates the operation of the transmitter after a time delay which is particular to that station. The system described has an outlying station A, Fig. 1, connected through an intermediate station B, Fig. 2, to a control station- C, Figs. 3 and 4, each having a perforated-tape transmitter and a typeprinting receiver. After an operator has perforated a tape, she inserts it in a transmitter and operates a " transmitter - start " key. The message will be transmitted in its proper turn under control of timing circuits provided at each station and having different delay times. The timing circuits are started up simultaneously by a signal constituted by a pause following an end-of-message signal. (comprising a " figures " signal followed by an H signal, a combination that cannot occur during a message). If this pause is sufficiently long (that is if no further message is immediately transmitted from the station controlling the line), a certain one of the stations will be given an opportunity to transmit either until all its messages have been sent or until a certain duration of time has expired, whichever is the shorter. Each station has a second timing arrangement, the time delays being substantially the same at all stations except the control station. When this duration of time expires while the station is in the act of sending a message, it will continue to send until that message is conipleted, but will then be cut off even if it has other messages waiting to be sent. The opportunity to transmit is transferred to the next station, next, that is, as determined by the first-mentioned timing circuits which are again started up by the pause following an end-of-message signal. When a station has been given its opportunity once in a cycle, its timing circuit is so conditioned that a much longer time must elapse before that station can start again, thus ensuring that all the other stations have their opportunity in turn. Initial conditions. Assuming that perforated tape has been inserted in each of the transmitters 101, 201, 401, and that the transmitter start keys 131, 231, 306 have been depressed, relays 136, 236, 320, 326 are energized, and the line transmission circuit is completed through relays 301, 302, 303, 120, 126, 220 and 226, these relays being all in their marking position. When power is switched on, relays 134, 234 are not energized and condensers 147, 247, 344 are charged through resistances 145, 245, 345a. The time constants of these circuits are such that 247 takes one second, 147 three seconds, and 344 five seconds to charge sufficiently to raise the potential of the grid of the associated valve 244, 144, 324 to permit current to flow to energize relays 243, 143, 318 respectively. At the end of about one second, relay 243 at station B energizes, thereby operating the start magnet 209 at that station and also a relay 242 which connects condenser 248 in parallel with 247, thus de-energizing valve 244 and relay 243. The start magnet releases distributer 207, thus causing the transmission of the message set up at station B. Transmission. During the transmission, relay 226 (station B) in response to spacing impulses energizes relays 239 and 234, the latter grounding the upper terminals of condensers 247, 248, so that these remain uncharged as long as transmission continues. The corresponding relay 126 at station A energizes relays 139 and 134, thereby grounding the upper terminal of condenser 147 and preventing the energization of valve 144 and relay 143, which would otherwise take place at the end of three seconds. Similarly, at the control station C, relay 302 prevents the energization of valve 324 and relay 318, and relay 301 connects condenser 343 in parallel with 344. Thus, transmission from A and C is prevented during transmission from B. At the end of the first (and each) message, the combination " figures " followed by the letter H is automatically transmitted. This combination, which cannot occur during a message, causes the contacts 124, 224, 450, 451 to be opened. At the transmitting station B, the opening of contact 224, opens one of two locking circuits of the relay 238, the other locking circuit being controlled by a relay 240, which is energized after a time determined by which of the condensers 256, 257, 258 has been associated with the grid circuit of valve 251 by depressing one or more keys 253 &c. The time constants of these circuits are of the order of minutes. If this time has not expired, relay 240 is not energized and relay 238 remains energized, so that the transmission of the next message proceeds. At stations A and C, the combination " figures " plus H operates contacts 124, 450, 451, but the original circuits are re-established as there is no pause after the transmission of the first message, so that the second and following messages are received in the same way as the first. If all the messages recorded in tape 203 are transmitted before the end of the time allotted for station B, the tape-operated contact 213 opens the locking circuit of relay 236 and consequently of relay 238. If all the messages are not transmitted within the allotted time, relay 240 is operated at the end of that time and at the end of the message then being transmitted contact 224 is opened as before. The release of relay 238, due either to the opening of contact 213, or to the operation of relay 240 and the subsequent opening of contacts 224, opens the circuit of the start magnet 209 to arrest the distributer and stop transmission. The transmission, at the end of the message, of the combination " figures " plus H, causes at station A the opening of contact 124 which opens the locking circuit of relay 139, which opens the circuit of the slowrelease relay 134. As the locking circuit of 134 remains open (since no spacing signals are passing through relay 126), relay 134 deenergizes, removing ground from the upper terminal of condenser 147, which now charges through resistance 145. At station C, ground is removed from the upper terminal of condenser 344, so that this now charges through resistance 345a. At station B, which has just finished transmitting, condenser 248 has been connected by relay 242 in parallel with condenser 247, so that the time constant of station B is now longer than that of station A. In these circumstances, relay 143 at station A operates before the corresponding relays at stations B and C, and transmission of the messages at station A takes place in the same way as at station B previously described. When all the messages at A have been transmitted, or, if the time allotted to station A has expired, at the end of the message then in process of transmission, the transmission of the combination " figures " plus H, causes at station C the removal of ground from the upper terminal of condenser 344 which now charges through resistance 345a. At this time condensers 147, 148 are in parallel at station A, and condensers 247, 248 are in parallel at station B, and the time constants of these circuits are such as to cause the corresponding relays 143, 243 to operate before condenser 344 is charged sufficiently to operate valve 324 and relay 318. Relays 143, 243 partially restore the circuits at stations A and B and disconnect the condensers 148, 248 from being in parallel with 147, 247. Shortly after, relay 318 at station C initiates a series of circuit changes which (1) prevent feeding of the tape 403, (2) energize relay 463 to connect the distributer contacts so that the combination " figures " is transmitted, (3) energize relay 464 so that the letter H is transmitted. The transmission of the combination " figures " plus H opens contacts 124, 224 at stations A, B to break the circuits of relays 139, 239, which open the circuits of slow-release relays 134, 234, but if a message is transmitted at once from the central station C, these relays remain energized over the spacing contacts of relays 126, 226 and maintain ground on the upper terminals of condensers 147, 247. After the transmission of " figures " plus H from station C, if there is a message ready for transmission, the normal tape feed is restored and the distributer released to transmit the message in the normal way. At the commencement of this transmission, a relay 330 closes the filament circuit of a valve 329, the grid of which is associated with condensers 340, 341, 342, one or more of which can be brought into circuit to determine the time allotted for transmission from the central station. When all the messages at C have been transmitted, or, if the time allotted to C has expired, at the end of the message then in process of transmission, the combination " figures " plus H at the end of the message restores the apparatus at the central station to normal, and also at stations A and B since no spacing signals follow immediately. The operations described above are repeated as long as any station has any messages to transmit. If, however, none of the stations has any messages to transmit, the valves 244, 144 and 324 and associated relays 243, 143, and 318 at stations B, A, C operate after one, three, and five seconds respectively, but without substantial result at stations A and B, except 'that condensers 148, 248 are connected in parallel with 147, 247 respectively, thus raising the time constants of these circuits to about five seconds, whereupon the relays 243, 143 are again energized, and partially restore the circuits to normal until signals are again received over the transmission loop. At the central