| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve reliability and certainty of actuation by measuring intensity of a resting signal by an actually nonexistent sound wave when a monitor is started, comparing intensity of the resting signal and intensity of an allowable resting signal with each other, and actuating an error recorder. SOLUTION: Intensity of a resting signal of an electric measuring signal is measured for time (t1 ) by an actually nonexistent sound wave with respective sound wave receivers 1 and 1', and when its intensity is 0, an error recorder 7 of the sound wave receiver 1 or 1' is actuated. When intensity of a measurement resting signal is larger than intensity of an allowable resting signal, a jamming sound wave exists, and the time (t1 ) is not started until the jamming sound wave is eliminated. In a sound wave reflected by being sent out by sound wave generators 8 and 8' after intensity of the resting signal is decided, the lapse of time of a measuring signal is calculated by a computer unit 2 through the sound wave receivers 1 and 1'. When it does not exceed intensity of the allowable resting signal in the time (t1 ) and/or does not reduce up to intensity of the resting signal in time (t2 ) continuing with the time (t1 ), the error recorder 7 is actuated.</p> |
