| 摘要 |
PURPOSE:To decide whether a distance varies actually or owing to device abnormality by comparing the quantity of variation in distance obtained by an ultrasonic measuring means with the maximum quantity of variation of a condition setting means. CONSTITUTION:A self-diagnostic part 19 compares the quantity of variation in distance per unit time from a time and distance arithmetic means 7 with the maximum quantity of variation from the condition setting means. At this time, when an actual measured value is larger than a set value determined physically by an object of measurement, the possibility of abnormality of the measuring instrument is high. When the quantity of variation in distance is larger than the set maximum quantity of variation, an output part 18 receives a signal from the diagnostic part 19 and keeps on holding the output right before the signal input, so that no wrong signal is outputted. At the same time, the diagnostic part 19 outputs a signal to a warning output part 22, which generates a warning output 21 indicating the abnormality of the device. |
