| 摘要 |
The invention relates to an electronic self-controlled alarm device. Set off conditions of the alarm are periodically established by varying alternatively into plus and into minus the resistance of the detection loop wherein are arranged detectors comprising a resistance in series with contacts. A self protection capacitive loop controls a square signal generator which produces: a) short pulses having the frequency f (self-protection), b) rectangular signals having the frequency 2f (self-control), verified at the terminals of the time delayed alarm relay. The cut-off or the shorting of a detector or of the detection loop sets off the alarm. The absence of self protection pulses or an incorrect frequency of the self-control signals sets off a fault warning device. The invention applies to alarm, surveyance, control, measurement apparatus and installations used for the protection against burglary and fire, in the industry, for the medical surveyance, etc.
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