Patent GB-256318-A (GB)
Title: Improvements in automatic and semi-automatic telephone systems
IPC: H04Q3/42
Filed: 1925-05-04
Abstract: 256,318. Standard Telephones &. Cables. Ltd.. (formely western Electric Co., Ltd.), Moir, R. A., and Hartley, G. C. May 4, 1925. Semi-automatic exchange systems.-In a coder in which the digits of a wanted number are recorded on a step-by-step switch PI and then transferred successively to relay register sets MWMZ - - UW-UZ under the control of digitmarking relays M - - S, the marking relays effect the connection of battery to the common point of the relay windings of each set so that only one set of contacts is required for this purpose and the number of springs on these relays is reduced. The coder contains means for testing as to the operative condition of the motor-driven interrupter springs MS for driving the code-sending switch CS, and if these springs are faulty an alarm is given and the coder is marked busy until a key BK is operated by an attendant. Detailed normal operation. When the coder is seized lamp SL lights over the earthed guarding conductor RT. Impulses incoming over wire PW pass through relay A to the stepping magnet DM1 of the impulse-receiving switch PI. Relay A remains operated during the digit and energizes relay B. At the end of the digit the relapse of relay A causes the partial operation of two-step relay M and also connects earth to wipers 1. 2, 3 of switch PI so that if, for example, the first (compensating) digit is 1, compensating relay N is operated over its left-hand winding, battery being supplied over resistance X and back contact 10 of relay M. Relay N inserts both resist. ances Y, Z in the code impulsing circuit. When relay B falls back, relay M operates fully and transfers the battery connection over resistance X from the compensating digit register F, N to the thousands register MW - - MZ. The numerical digits are thus recorded in succession on the register sets MW - - MZ, &c., the relays P - - S controlling the battery connection to the operating (left-hand) windings of the relay sets in turn. At the completion of the last digit, the relapse of relay A operates relay S partially and also completes a circuit for relay D which energizes relay J and locks up over the outgoing trunk conductors. Relay J starts the motor for driving the interrupter springs MS. When the apparatus at the distant manual exchange is ready to receive impulses, relay D is unlocked and completes a circuit from the earthed lead RT over contacts C6, S16, D6, wiper P of switch CS, and springs MS for the left-hand winding of two-step relay K which operates partially as soon as the springs close and fully when they subsequently open. Relay K completes a holding circuit for relay J and also extends the interrupter circuit to the magnet DM2 of switch CS, which is thus stepped round at a uniform rate, a series of code impulses of varying strength and polarity being transmitted over leads - and + in accordance with the setting of the relay registers. At the conclusion of the last digit, relay C operates in series with magnet DM2. operates a meter MT, earths lead PW to cause the connection to be switched through, and unlocks all the register and digit-marking relays. Faulty interrupter springs. If the springs MS are faulty, relay K does not operate completely, relay J falls back, and an alarm circuit AL is completed. Earth is connected over contacts C6. S16, D6, S14, J6, C8 to the lead PW to cause the connection to be switched through to the manual exchange at which the call may be passed to a special operator. Relay E is operated at this time and maintains earth over its contact 10 on the guarding wire RT until the key BK is thrown by an attendant. Premature release. If the calling subscriber hangs up either during dialling or during codesending, relay E remains energized over one or other of its windings and off-normal banks of the switches PI, CS and maintains the coder busy until any operated relays and switches are fully restored to normal. Specification 253,583 is referred to.