Patent GB-498492-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/00
Filed: 1937-07-09
Abstract: 498,492. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and HYDE, G. A. M. July 9, 1937, No. 14354/38. Divided out of 498,416. [Class 40 (iii)] An operator, Fig. 4, at a distance from an automatic exchange over a line L1, exercises the same functions as if at the exchange, Figs. 2, 3. The operator can assist a subscriber, Fig. 1, who has an urgent call for another subscriber already engaged. The exchange circuit of Fig. 2 is individual to each subscriber, and the wipers SP, CL, T, RC, TR find contacts which are connected to the corresponding lines (left of Fig. 2) of the called subscriber. Fig. 3 shows the exchange circuit which is individual to the operator. The dialling by the subscriber, marking a called line busy or unobtainable, the establishment of normal communication, and the release, either by a subscriber or automatically, are described in Specifications 498,416, 498,425, and 498,428. Calling an operator. The subscriber actuates a key OPK to operate a relay SOP and hence a relay ST if not already operated. A circuit is closed for a relay MS, if not already energized, and the motor M started. Normal transmitting contacts TTC are replaced by contacts RSS, which are operated by wards on the " answer back " cam, tripped by a magnet ABM, to send long space, short mark, long space, short mark. A relay LD has been energized, but the earth on a send-receive switch SRS, which normally short-circuits a line relay LR, is removed. The first long space signal operates a relay SA, releases a relay SBR, and energizes a relay WR. On the following marking signal, the relay SBR is re-energized, and a relay XR is energized, but the signal is not sufficiently long to allow the relay SA to release. On the second long spacing signal, the relay SBR again releases and energizes a relay YR. After the last marking signal, the relay SA releases and operates a relay ER, which releases the relay WR, and hence relays XR, YR, and itself, thus erasing the signal. Action at exchange before establishment of a communication. The first spacing signal in a telegraphic relay SS, which is associated with a line relay LLR, operates a relay LDR, which operates the vertical magnet VM of a selector switch relay DC, and relays LG, SB, which operates a relay XBR to break the circuit of the relay SB. This relay, which is too slow to be released by normal signals, is released by the long space signal to operate a relay W. On the following marking signal, the relay SB is re-operated, a relay X operates, the vertical magnet takes one step, but the relay DC is too slow to release and a relay NU is not operated. On the second long space, the relay LDR is again released, and the relay SB released and operates a, relay Y. At the end of this signal the relay SB is again operated, the vertical magnet steps the wipers to the second level and, after the relay DC has released, the relay NU is energized, but, since neither relay AB nor BB is operated, the indication " number unobtainable " from a lead NU is not sent. After the relay LDR has released, the relay LG releases to close a circuit for the relay RC and release the relays W, X, Y. The relay RC closes a circuit for a relay OP, which connects the subscriber's exchange circuit to the operator's exchange circuit and operates a relay ON. A relay M, Fig. 3, breaks the original circuit of the relay OP to prevent the connection of other subscribers and energizes relays OH, OST. The relays TR, SS are now in circuit with corresponding relays OTR, OSS in the operator's exchange circuit. Lead CN, Fig. 2, is connected to a cam which sends a space signal of 70 milliseconds followed by a marking signal of 1¢ seconds and then the subscriber's number. Continuously operating cams also apply to leads PU, TO, Figs. 2, 3, a brief earth respectively before and after these signals. The earth on the lead PU, Fig. 3, energizes a relay OAB, which substitutes the sending contacts in the exchange for contacts llr, Fig. 2. The relays OTR, OSS, Fig. 3, respond to the impulses, a relay OSB remains energized, energizes a relay OBR to lock the relay OST, and connects the line L1 to the operator's substation, Fig. 4, to negative battery. The relay OTR repeats the impulses to the operator's substation where they operate a line relay LRO. The first space signal energizes a relay SSO to operate a relay MSO which starts up a motor OM. At the end. of the subscriber's number, earth on the lead TO, Fig. 3, operates a relay OTO which breaks the locking circuit of the relay OAB to restore the circuit between the subscriber's relays TR, SS and the relays OTR, OSS. Following the last signal, the relay OSB releases and breaks the circuit of the relay OBR, but before this a circuit is closed for a relay CL, which releases the relay OTO. When the operator's sendreceive switch OSRS is at s, a relay DSO is operated and transmitting contacts OTCC send the required signals to the subscriber. Action if subscriber is engaged in a communication. The operation of the subscriber's key OPK causes the circuits of the other subscriber to respond as described above up to the operation of the relay RC, Fig. 2. This cannot energize, but, after the relay LG has released and before the relay W releases, earth is extended over the lead SP to the exchange circuit of the subscriber, who has actuated his key, and there operates the relay RC. Thereafter the circuit changes proceed as above, and the operator communicates with both subscribers. A release signal by a subscriber does not now affect the connection to the operator, although it releases the connection between two subscribers. Operator connecting to a subscriber. When the operator's dial, Fig. 4, is moved off normal, a relay DRO operates, and a relay DNO operates the relay MSO and renders the relay DRO dependent solely on the impulsing contacts of the dial so that it connects spacing and marking potential to the line L1. At the exchange, Fig. 3, the off-normal marking potential causes a relay OS to operate a relay OSM. The spacing dialling impulses cause the relay OS to operate a relay OSR to prevent subsequent operation of the relay OSM and to operate a relay OLG. A polarized line relay OLR produces opposite currents in the lower and middle windings of the relay OTR, which remains in the marking position. The current in the lower winding of the relay OSS overcomes the biassing and a relay ODR is operated followed by a relay C and the vertical magnet OVM of the operator's selector switch to raise the wipers to the required level. At the first impulse the relay ODR operates the relays OSB, OST and hence the relay OBR and the circuit of the release magnet OZM is broken. The slow-release relay C releases only on the completion of the digit and closes a circuit for a relay OE, which changes the impulsing circuit to the rotary magnet ORM. At the end of the second digit, the relay C releases and, before the relay OE his time to release, closes a circuit for the relay OH, which energizes relays BH, OP, Fig. 2, and hence the relay M, Fig. 3. When the operator's dial returns to normal, her relays DNO, DRO return to normal and the operator may communicate with the substation. To start the subscriber's teleprinter, she actuates her space key and the relay DSO is energized to connect marking potential to the line L1, and thereafter the contacts OTCC send the required signal of a space followed by a mark. These signals are repeated by the relay OLR to the relays TR, SS of the subscriber. As the relay ON is operated, the subscriber's selector switch is not operated, but the signals are repeated over the line L to the substation. Urgent call for engaged subscriber. The calling subscriber calls the operator and the operator communicates with the wanted subscriber, as described above. If the latter is in an existing connection, the operator's relays OTR, OSS are in the circuit of the relays TR, SS and the operator records the messages and can intervene appropriately. If the call is accepted, the operator operates the selector switch of the accepting substation. The operator actuates a key EDK to operate a relay ED and dials the number. The dialling impulses now consist of marking impulses, which operate the relay OS and hence the relay OSM, Fig. 3. The lower windings of the relays OTR, OSS are shunted, and the relay LDR, Fig. 2, operates the subscriber's selector switch. Release by operator. The operator sends a long mark by actuating a key ORK, which energizes the relay ED followed by the relay DNO. The marking potential operates the relays OS, OSM, Fig. 3, for sufficient time for the relay OSB to release and break the circuit of the relay OBR after a circuit has been closed for the relay CL which breaks the circuit of the relays M, OP. The circuit of the release magnet OZM is completed, that of the relay OH broken, and the operator's exchange circuit is restored to normal. To release a connection between two subscribers, the key TK, Fig. 4, is operated to send a spacing potential, which operates the relays TR, SS, Fig. 2, to spacing to release the subscriber's selector switch.