Patent GB-398270-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1932-03-21
Abstract: 398,270. Exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, COLLYER, J. E. and MOSS, B. F., c/o General Electric Co., Stoke, Coventry. March 21, 1932, No. 8334. [Class 40 (iv).] In a system in which subscribers' lines are branched from a common switching installation on a line to a manual or automatic exchange, all the operating current for the switching installation is derived from the exchange and selection is effected by means of impulses over the line which comprises only two wires. Individual meters are provided at the exchange. In the systems described, the switching station comprises a counting chain of relays which remain in their " make " position until reset which on outgoing calls acts as a call finder and delivers impulses to the exchange line to operate an identifying switch and on incoming calls acts as a numerical selector receiving impulses characteristic of the terminal or jack over which the exchange line is seized. Construction of switches. The switch MB has a " masking cam " which connects together all the terminals except that with which the single wiper is in contact Outgoing calls-association of subscriber with junction. When any subscriber calls the common line relay B at the exchange pulls up in series with the individual line relay AZ .. FZ (which is of a type, e.g. as described in Specification 354,847, which remains in its operated position until reset) over a high-resistance winding and energizes C. C shunts the highresistance winding of B by its low-resistance winding to allow the relay AZ .. FZ to pull up and the relay AZ .. FZ opens the initial circuit over the junction to release B and C. This method of mutual control between relays at the exchange and the satellite which is used repeatedly in the circuit operations to be described will be referred to for brevity herein after as a "to-and-fro" signal. B on falling energizes D which locks up and connects J, W to the + and - wires respectively. W pulls up over a high resistance winding in series with N and energizes F which shunts the high resistance winding of W to enable N to pull up and connect S to the + wire, whereupon J and S pull up in series. S energizes the 1st relay AX of the counting chain AX .. FX (the relays being of the type referred to above). AX energizes SS which removes the low resistance shunt from N to release W, F at the exchange. The latter removes the shunt from the high-resistance winding of W to release N at the satellite. N releases S to reconnect the lowresistance coil of N and so reoperate W. The cycle is then repeated, except that for the even impulses SA takes the place of S, until the counting relay corresponding to the calling line is energized. Relay M (which is of the type referred to above) then pulls up over the + wire, cuts off itself and the counting chain, releasing W, J at the exchange, connects the subscriber's line to the junction and disconnects the other line relays. At the exchange, G pulls up and locks on the 1st operation of J and F gives impulses to the stepping magnet of MA which thus registers the calling number. Outgoing call-completing and metering manually. When J is released, K pulls up releasing D, G and extending the line over wipers MA1, MA2 to the subscriber's jack, LA pulls up over the loop and lights the calling lamp. When the operator plugs in, the sleeve relay AK.. FK energizes all the relays AG .. FG except that corresponding to the calling line in series with SL which busies the line at the other jacks and cuts off LA and ground from the junction. The individual meter which is connected to the sleeve over a back contact of the relay AG .. FG is operated from the cord circuit in known manner. Outgoing call-completing and metering automatically. In this case LA, which is energized by K as before, starts the line switch LS, Fig. 4, which on going off normal busies all the appearances of the line in the final selectors and then hunts under control of SL. The call is metered in known manner on the individual meter selected by MA, which is controlled as in the manual system. Release. The relapse of SL following that of the sleeve relay AK .. FK or of the release relay in the 1st selector (not shown) energizes R which connects RR and ground to the + and - wires respectively. Relay Y, which is bridged across the junction at the satellite in series with a rectifier pulls up in this circuit and connects the re-setting coil of Q to the + wire to initiate the re-setting in succession of all the two position relays, the bridge through Y to hold RR at the exchange being maintained over one or more contacts of these relays in parallel until they have all been restored. RR makes a homing circuit for MA and holds itself until the switch has been restored. Signalling class of call to operator or automatic apparatus. Certain calls, e.g. those from prepayment stations, give a flashing call signal over MA5 instead of a steady signal over MA3 or, in the automatic system, give a discriminating signal over MA2, Fig. 4. Incoming call. When the operator plugs in, the individual sleeve relay energizes the relays AG .. FG (except that of the wanted sub-station) and SL which locks up. In the automatic system, ground on the seized test wire P1 .. P6 energizes HO which energizes SL. In both cases SL energizes T which connects B to the - wire to initiate a " to-and-fro " between B and Q resulting in the operation of Q at the satellite and D at the exchange. D connects J and W to the + and -- wires respectively and H pulls up in series with J and energizes HA. J energizes G and interaction proceeds as in an outgoing call between W, F at the exchange and N, S, SA and the counting chain at the satellite, F repeating the impulses to the switch MB, until wiper MB3, Fig. 3, or MB2, Fig. 4, finds the terminal corresponding to the wanted sub-station. CO then disconnects W, J and energizes JB which connects XA to the + wire to initiate a " to- and-fro" signal resulting in the energization of the wanted line relay AZ .. FZ at the satellite and of YA at the exchange. Z, ZZ, M then co-operate in a " to-and-fro " signal over the - wire resulting in the energization of M to connect the subscriber to the junction at the satellite and of QA, K at the exchange to extend the junction to the jack or final selector. Reverting call-manual system. When the operator plugs into the wanted jack, SC pulls up, since the relays AG .. FG (except that of the calling party) are energized, energizes R and releases AG .. FG to allow the sleeve relay of the wanted party to pull up. SC is held over resistance SR (over which it could not pull up) and holds SL. R makes the releasing circuit RR, RE, Y to restore the satellite relays but the homing circuit for MA is held open by SL. When the satellite has been reset, RR, K, R fall back and T pulls up to initiate interaction between the satellite counting relays and the exchange apparatus until MB finds the terminal marked by the wanted sleeve relay. Marking by the calling sleeve relay is prevented by the corresponding relay AF .. FF. CO, JB, XA, the wanted line relay, ZZ, M, QA and K are then operated as in an incoming call, but since SC is operated the line is rung over a winding of E instead of from the cord. When the wanted party replies E switches the line through to the feed in the cord-circuit and RT pulls up to re-operate the calling line relay, but is at once shunted out by CK to prevent interference by other subscribers. Reverting calls-automatic system. The system shown does not provide for reverting calls but storage apparatus may be provided in the junction to give this facility, the line being rung as in the manual system and unnecessary apparatus in the exchange being released. According to the Provisional Specification the storage apparatus consists of a uniselector which responds to the 1st 3 digits to discriminate between reverting and ordinary calls. Modified system in which a single switch replaces MA, MB. If revertive calling facilities are unnecessary the switch MB may be omitted and a bank corresponding to MB3 is provided on MA and is connected up only on calls outgoing to the switching station e.g. by a contact of SL. Similarly wipers MA3, MA5 are connected up only on calls incoming from the switching station.