Patent GB-623184-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/42
Filed: 1946-02-01
Abstract: 623,184. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and CHRISTIAN, D. A. Feb. 1, 1946, No. 3328. [Class 40 (iv)] A control circuit comprises two digit switches (each with its associated dialling relay) on which incoming digits are registered alternately, the hunting period for each selector switch commencing after the release of a dialling relay for the appropriate digit and ceasing just before the release of the other dialling relay after the reception of the subsequent digit. The testing of outlets from the selectors is performed in the control circuit by a polarized test relay which is connected across a numerically selected pair out of four marking wires. The marking wires, two of which are provided by the speaking wires, are switched through together with a selector drive wire over wipers of each selecting switch to control the subsequent switch. On seizure, preparatory relay GN in the first group selector and impulse and release relays A and B in the control circuit operate, followed by relay R and dialling relay CA. The first digit is registered on switch DA, L operating at the first impulse followed by change-over relay SA. When the dialling relay CA releases, R, which was held over its lefthand coil, releases, so maintaining SA operated by removing a short circuit from its holding coil and the second dialling relay CB operates. Release of relay R also completes a circuit for the polarized test relay T over two of the marking wires, +, -, W, X, selected by the wipers DA1, 2 of the digit switch DA. Relay R further completes a circuit over wire l for the drive magnet LM of the selector which hunts to find a free outlet whose contacts in banks 4 and 5 are connected to the selected marking wires, whereupon the test relay T is energized by battery on the p-contact, and stops the selector. Relay R operates followed by TT which puts +ve battery on the p-wire to operate the selector switching relay GS, which locks to the subsequent earth thereon, releases GN and switches through to the next stage, whereupon T and TT release but not R, which is held over a contact of CB. Meanwhile, SB is energized in place of SA and the next digit is registered on switch DB. When the dialling relay CB falls back, R releases and the second selector hunts for a free outlet marked by switch DB, relays SB, CB functioning similarly to SA, CA. All outlets busy. The selector switch rotates to its last contact where +ve battery from the p-terminal is reverted over bank 4 and the + wire to operate BT which stops the switch and returns busy tone to the caller. Final selector. This selector is of the non- homing type and is provided with four marking banks, 6, 7 being used for the tens marking and 4, 5 for the units marking. After the tens marking has been picked up, marginal relay FR operates to the +vc battery on the p-wire. locks to the subsequent earth thereon, and transfers the marking circuits to banks 4, 5 and the selector then hunts for the marking in the subsequent decade. When this is found, FS operates in a manner similar to FR, which latter is released, thereby reverting a +ve battery pulse along the l-wire to operate F which connects up ringing current and tone. Ring trip relay TR operates on reply, switching in feed relay Y, metering battery being applied to the p-wire during the consequent slow release of L., The first positions of the 2nd ... 5th decades carry both tens markings on banks 6,' 7 and marking for the units digit 1 on banks 4, 5. The first position of the first decade, however, carries no outlet, being reserved for the tens marking only, the next position carrying the marking for the units digit 1. This avoids the possibility of T failing to release when FR operates, which might occur if identical markings for the tens and units digits were present at the same position. Called subscriber busy. The last position of each decade causes +ve battery to be connected to the + wire over bank 8, so operating the busy relay BT which stops the switch and reverts busy tone. Since this position also corresponds to the last line in the decade, the marking for this digit in banks 4 and 5 is arranged not to involve the + wire. If this particular line is required and is free, both T and BT will. operate, but BT will immediately be released by TT. PBX groups. All lines of such a group may be given the same marking, the busy. markings at the end of one or more decades being removed if a group of more than 10 lines is required. Alternatively, the busy markings may be removed, but the numerical markings kept unchanged, lines with the same units marking constituting lines of one of ten PBX groups. Outgoing junctions. These may be connected to any group selector, but must be sufficiently early in the bank to allow the search to be completed during the inter-train pause. When a group selector switches through to a junction, earth and battery connected to banks 6, 7 operate J followed by TR and F and feed relay Y is replaced by back-bridge relay D. Relay J prepares a circuit for CA which thereafter operates at the first impulse of each succeeding train to place a low impedance loop across the outgoing line over which relay A repeats the digits. On switch through at the distant exchange, D operates releasing L and metering the call. Large junction groups. Groups of junctions which are too large to be searched during the inter-train pause may be connected to separate banks 11, 12 and 21, 22 of a modified first group selector, Figs. 4, 5, the first pair of arcs catering for 50 junctions designated by any of the digits 1, 8 or 0 and the second pair for 50 junctions designated by digits 3 or 7. To avoid the use of extra marking banks such as 5, wiper switching relays GJ, GK (one or both of which operate on a junction call over a third bank of the digit switch DA) apply earth markings direct to the - wire or the W wire according to whether outlets from banks 11, 12 or 21, 22 are required. Relay J operates over DA3 at the end of the search. The control circuit may be common to a number of first group selectors and other means of marking may be employed, e.g. by using different electrical conditions applied to the terminals (of an arc) of a selecting switch to characterise the outlets therefrom, as described in Specification 623,177. Further features of the system are claimed in Specifications 623,262 and 623,263.