Patent GB-258962-A (GB)
Title: Improvements in or relating to automatic and semi-automatic telephone systems
IPC: H04M3/08
Filed: 1925-07-04
Abstract: 258,962. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd.), Moir, R. A., and Hartley, G. C. July 4, 1925. Semi-automatic exchange systems.-A coder for transmitting the numerical part of a wanted number in code impulses to control a numberindicator at a manual exchange comprises the following features :-(1) If the impulse-receiving switch remains off-normal when a succeeding digit arrives, an alarm signal is given and the calling subscriber is switched through to a special operator at the manual exchange. (2) If the impulse-receiving switch remains off-normal after the last digit has been received, the coded number is sent out as usual and an alarm is given when the code-impulsing is completed. (3) If the calling subscriber hangs up whilst the impulsereceiving switch is stuck off-normal the preceding switches are released and the coder is then marked busy. (4) If the code-sending switch fails to complete its operations, a delayed alarm is put into operation when the calling subscriber hangs up. (5) If the calling subscriber hangs up during code-sending, coding continues but at the end of this operation the apparatus at the manual exchange is released. The coder shown also gives alarm if the code-sending switch does not move off-normal owing to faulty interruptersprings. Normal operation. When the coder is seized, relay MC operates over lead RT to start the motor for driving the springs IS2 and to light supervisory lamp LP. The impulses of the first digit pass over circuit PW, CO 8, US 26, SP, to the stepping magnet DM 1 of the impulsereceiving switch PR, and at the first step of the switch relay SC operates over the off-normal bank P. At the end of the digit during the interval between the release of relays SP, SC, earth from bank P is connected over contacts SP 6, SC 8 to two-step relay CT and over contacts SP 6, SC 10 to wipers 1 - - 3 of switch PR to effect the operation of the appropriate relays of the storage group HC, LC. Relay SA also operates over bank P and, on the release of relay SC, closes a restoring circuit for switch PR. Succeeding digits are received in a similar manner and at the end of the last digit relays US, LS operate in parallel, the latter locking over the trunk to the manual exchange. When the latter is ready to receive the code, relay LS is unlocked and completes parallel circuits over wiper P of the code-sending switch PS for magnet DM 2 in series with motor-driven springs IS 2 and for relav SA. Switch PS is thus stepped round and the transmission of code impulses proceeds in known manner. At the end of this operation, relay CO operates to extend earth over lead FW to operate a meter EM, and to release the relays of the coder. Faults. If the switch PR is off-normal when the first impulse of the next digit arrives, relay SA is operated and the impulse passes over contacts CO 8, US 26, SA 6 to relay PA which locks to the release key BK, closes an alarm circuit IA, and flashes the lamp LP. Relay PA also operates relay SC over the circuit PW, PA 12, US 32. Relay SC will similarly operate for each succeeding digit so that the relays MS - - US will operate successively. Upon the release of relay LS from the manual end, earth is immediately connected over contacts LS 8, US 32, PA 12, CO 8 to the wire PW so that the call is switched through to the manual end without any transmission of code impulses and may be completed by a special operator. If the switch PR remains off normal after receiving the last digit code-impulsing proceeds as usual but, when relay CO operates, alarm relay PA is energized over wiper P of switch PR. If the switch PS does not step off-normal, the release of relay MC after an interval removes a short-circuit from the lower winding of relay PA which operates over wiper P of switch PS in its normal position to give an alarm. If the switch PS sticks offnormal during code-sending, relay SA is operated and when the calling subscriber hangs up an earth on wire PW operates relay SC which closes a circuit from earth at wiper 1 of switch PR over contacts SO 10, SC 8, CT 11, MS 11, US 13, SA 11 to battery SM over a supervisory signal. Premature release. If the calling subscriber hangs up whilst switch PR is stuck off-normal, earth on lead PW operates relay SC which temporarily removes earth at contact SC 6 from the lead RT so as to release the preceding apparatus, this earth being restored when relay SC releases to mark the coder busy. If release occurs during code-sending, code-sending is completed and in the 22nd and 23rd positions of switch PS, earth from lead PW is connected over contacts COS, PA 12, US 26 to the + ve, out-going line to effect release of the apparatus at the manual end.