| 摘要 |
PROBLEM TO BE SOLVED: To warn an abnormality of topographic features of observation points by a simple setting without laying wire rods or the like. SOLUTION: A time for waves to travel from a detecting part body 1A to a detecting part body 1B is greatly shorter than a time for ultrasonic waves to travel from the detecting part body 1B to the detecting part body 1A and is substantially negligible. Therefore, when a time after the waves are emitted from the detecting part body 1A to the detecting part body 1B before the ultrasonic waves return to the detecting part body 1A is measured, distance data between the detecting part bodies 1A and 1B can be calculated by a simple setting without laying wire rods between the detecting part bodies 1A and 1B, and an abnormality of topographic features of observation points can be generated as a warning.
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