Patent GB-646648-A (GB)
Title: Improvements in burglar or fire alarms
IPC: H04M11/04
Filed: 1947-05-14
Abstract: 646,648. Automatic exchange systems. AUTOMATIC ELECTRON ALARMS (PRO. PRIETARY), Ltd. May 14, 1947, Nos. 13050, 13051 and 13052. Convention dates, May 29, 1946, Aug. 16, 1946, and March 28, 1947. [Class 40 (iv)] An alarm system in which a recorded message is transmitted over an automatic telephone system to a preselected substation includes a sound recording of an impulse train, the recorded impulses being reproduced as electrical dialling impulses for obtaining the required sub-station. As shown, a rectified alternating current supply from a transformer T1 holds relay A operated in series with a protective circuit C and locks up relay B independently of A. Breaking of the protective circuit C, or closing of a circuit D, releases relay A. Relays E, F and H thereupon operate, connecting a floodlamp V and a siren W to the supply mains, and a valve heater circuit to a winding S4 on the transformer. As soon as its cathode attains operating temperature, valve V4 supplies a rectified anode potential to the valves V1, V2 and V3. Anode current due to the valve V3 operates relays I, J and K, thereby completing a gramophone motor circuit O and connecting a telephone line P to a coupling transformer T2 in the anode circuit of the valve. A gramophone pick-up circuit Q is connected to the grid of the portion V1a of valve V1, the pick-up co-operating with a disc recording of dialling impulses followed by a warning message. The dialling impulses are recorded on the disc at a substantially higher frequency than that of the warning message. The signals from the pick-up circuit are amplified by the portion V1a of the valve VI, the high-frequency impulses being passed through a high-pass filter Z and further amplified by the portion V1b of the valve V1. The high-frequency impulses are then applied to the grid of valve V2 through a blocking condenser Z1 which resonates with a seriesconnected choke C1 at the impulse frequency. The valve V2 is normally biassed so that there is little or no anode current; the voltage across C1 at the impulse frequency, however, creates corresponding current pulses in the anode circuit which operate a relay N, thereby interrupting the telephone circuit and reproducing the recorded impulses as a dialling train. After an inoperative time interval to allow the called party to reply, the dialling impulses are followed by a warning message which is amplified in the portion V1a of valve V1 and further amplified by a valve V3 coupled to the telephone line. Warning messages may be transmitted to several sub-stations in turn, the end of each message being followed by a period during which a continuous high frequency recorded signal operates relay N to open the telephone circuit and release the previous connection. At the completion of all the messages the pick-up arm closes contacts Y. Relay G locks up and disconnects relay H to open the valve heater circuits. Relays I, J and K release, stopping the gramophone motor and disconnecting the telephone lines from the apparatus. The siren and floodlight remain operative until relays E and F are released by opening a main switch a. A pilot light P1 may be provided to indicate when relay A is closed and a further light P2 to indicate when the valve heater circuit is switched on.