Patent GB-441642-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: H04L12/18
Filed: 1934-09-07
Abstract: 441,642. Electric selective signalling- systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and LIMB, F., c/o Ericsson Telephones, Ltd., Beeston, Notting- hamshire. Sept. 7, 1934, No. 25755. [Class 40 (i)] In a system for signalling stock quotation or like indications from a central station to subscribers connected to the station through sub-centres when the subscriber's unit has been set to indicate the price of a given stock the line between the sub-centre and the central station is freed for use by another subscriber. If more than one subscriber is calling, the subscribers are each limited to a single quotation until waiting subscribers have used the circuit. As shown three selecting digits and three quotation digits are used, the digits being sent over individual wires, and signalling takes place in both directions over the same wires. Two conductors per digit may be employed, selection being by the combination of potentials on the two conductors. Instead of providing separate wires for each digit, the digits may be sent concurrently over the same wires. Check-back signals may be provided. The apparatus at a subscriber's station is shown in Figs. 1 and 2, that at the sub-centre in Figs. 3 and 4, whilst Figs. 5, 6, 7, 8 and 9 illustrate the apparatus at the main station for receiving and transmitting a single digit. When the subscriber wishes to known the price of a stock, selecting keys such as KY1, KY2, KY3 are operated. The keys shown are some of those for one digit only and it is assumed that KY3 is operated and relay I energized. Keys for the other digits control relays 1A and 1B (not shown) so that when one key in each of the three sets has been operated, relay SS is energized and locks. Relay Y (Fig. 3) is energized over line 1 in series with relay PA, which does not operate. Relay Y locks and, if the line to the main station is free, relay X pulls up, locks, releases relay Y and puts earth on common conductor 10 so that the switching relays of other subscribers, such as relay XA would be shorted and prevented from operating. The contacts y2, ya2 &c. of the various subscribers' units are connected in series so that an order of precedence is provided if subscribers call simultaneously. A "hold-off" relay HO is also provided for each subscriber which energizes when the subscribers switching relay X pulls up and remains energized so long as a calling relay Y of another subscriber is operated. The " hold-off " relay prevents the operation of the calling relay Y of a subscriber who has been supplied with one indication until any other calling subscriber has used the line. When the switching relay X has energized, the lines 1-4 are connected to the main station lines 5-8. The digit represented by key KY3 is transmitted over line 4, 8 and positive battery from spring 17 is connected over 19, 20, ql, q2, p1, O line 4, st6 to ZAX. Relays O and ZAX energize. At the transmitting station relay P pulls up to open the short across resistance 25 whilst at the main office relays AM, ST and AX pull up to bring resistance 22 into circuit. When the line includes both resistances, relays O and ZAX fall away, relay P locks in series with Q and relay AX in series with JX so that the resistances are again shorted and spring 30 is connected to line over s1. Relay ZAX is again energized as the current flow is from positive and relays CX and R pull up, followed when O and ZAX fall away by KX and S. The potential on spring 33 is negative and as this is now connected up relay ZBX and not ZAX is energized so that FX pulls up to be followed by MX whilst at the subscribers' unit relay T is followed by U. The spring 36 is now operative over w1 and ZAX responds so that GX pulls up whilst V and W, Fig. 1, open the transmitting circuit. As relays AX, CX, FX and GX are up the relay N, Fig. 9, is selected over lead 37. Simultaneously with the selection described above the other digits of the wanted unit are transmitted over leads 2, 6 and 3, 7 and it is assumed that these digits have selected relays NA, Fig. 9a, and NB, Fig. 9b, so that relays AA and AB relative to the wanted stock are selected and energized in series with relay CZ. The units of the wanted stock comprise keys such as KY17 which can be set to any one of sixteen positions and in each position connect contacts 11-14 to positive or negative in different combinations so that when the relay AA relative to a stock is energized, the contacts 11-14 connect code potentials to contacts of transmission relays QX, SX, UX and WX. The energization of relay CZ in series with AA and AB prepares the central station equipment for transmission and allows relay PA to energize over line 1, 5, relay CD being shorted by rectifier 40. The energized relays P-W are released and the incoming lines are switched over for reception. Transmission takes place exactly as described above, relays PX-WX connecting up the terminals 11-14 in turn and relays A-H being operated in accordance with the impulse train. With the key KY17 in the position shown a code of - - + + is transmitted so that relays B, D, E, G are energized and lamp L4 is lit. The other digits of the quotation are simultaneously transmitted over the other line wires. When the transmission is completed, relays WX of each digit transmission relay set PX-WX is operated so that relay ST is released and the main office equipment restores. At the subscriber's unit, relay Z operates in series with the indicator lamps and when the Z relays of all digits are energized relay SS is released. The indication is maintained as relays A, H are held by a contact of relay Z until the operated selection keys are released. When relay SS is released, relay PA falls away and relay CD, Fig. 4, is energized to release the calling relay X and allow the common line to be used by another subscriber.