Patent GB-537050-A (GB)
Title: Improvements in or relating to line identification for telephone systems
IPC: H04M15/08
Filed: 1940-01-04
Abstract: 537,050. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. Jan. 4, 1940, No. 210. [Class 40 (iv)] The number of a line and, if desired, the exchange name is announced to an operator by phonographic apparatus controlled by storage apparatus set by signals transmitted from line identification equipment. The identification equipment may be of the type described in Specification 525,902 but employing a signalling code of four voice-frequency pulses per digit. Each pulse comprises one frequency which steps a receiving switch and selected pulses indicative of the digit comprise a second frequency which operates register relays for controlling the announcing apparatus. The announcements are useful for toll operators, or for maintainence officers in case of permanent-loop conditions. When the operator has responded to the call and thrown speaking key KSI, relay SK connects the cord to the position circuit and energizes SKR which is followed by MN to disconnect the monitoring transformer MTR and by HR which operates SP. If the operator requires line indentification, she throws key KRI to operate SW which releases sluggish relay SP to connect up the voice-frequency receiving relays PA, PB, a pulse of 50# being transmitted in the meantime to start the identification equipment. Relay PA responds to 50 # in every pulse of the identification code to step switch R the magnet RM of which is maintained energized for the full stroke by relay PC controlled over the interrupter contacts. A 150 # component in a pulse operates relay PB which energizes the corresponding relay of register WA....ZA and corresponding registers for successive digits. The operator initiates the announcement by throwing key KI which releases MN to connect the secondary of the monitoring transformer MTR over contacts of selecting relays WS.... ZS to the speech coils 1-0, and operates M to connect her receiver OR to the primary of the transformer. The monitoring transformer is preferred to the ordinary listening transformer STR in view of its higher impedance. After the first digit has been received, IG operated over R3 brings up a common start relay ST if not already operated, and pulses from SMC covering speech periods in the speech coils are connected to PAS. If PAS happens to be already pulsing, IG is short-circuited until PAS is in the unoperated condition. Relay IG connects the speech coil selecting relays WS....ZS to back stroke switch S which connects up the registers in turn in response to impulses from PAS. and relays WSZS connect the required speech coils to transformer MTR. Switch S stops after being stepped for the maximum number of digits provided for, and is homed by the relapse of IG when the key KI is restored. Re-depression of the key causes repetition of the announcement. When the speaking key KS is restored, removal of a short-circuit operates GR which lights lamp LP, shunts down SK and releases HR whereupon switch R is homed. In multiexchange areas, the exchange digits or some of them may be used to announce the exchange name or its abbreviation. Automatic cut-off after receipt of 4, 5 or 6 digits. Sluggish relay SW is maintained over R1 except in positions 17, 21 and 26 at the end of the above digits. If the switch stops in one of these positions, the relay falls back and disconnects relays PA, PB from the cord circuit. Faults.-If switch R or S fails to go home, GR remains operated to bring in an alarm. If the identification signals are faulty, R fails to step and SW is not released so that alarm relays TA, TB operated by " S " and " Z " pulses cause lamp LP to flash, and also operate an alarm.