| 摘要 |
PROBLEM TO BE SOLVED: To provide a nondestructive test device of concrete capable of detecting precisely and surely an internal crack of a concrete product. SOLUTION: An external force applied to an ALC board 1 by a hammer 2 for generating a hammering sound is detected by an exciting force sensor 11, and the ratio thereof to an external force reference value is determined by a ratio computing unit 15. The hammering sound generated on the ALC board 1 is detected by a microphone 3, and separated into time series signals in each frequency zone by an analog BPF 5, and rectified and instantaneous maximum values in each frequency zone are extracted by a peak hold 7. The maximum values are corrected based on the ratio calculated by the ratio computing unit 15, and compared with a vibration reference value set up beforehand by a comparator 9. When the result is out of the prescribed relation, comparison result signals are issued, and if the number of the comparison result signals is, for example, three or more, an alarm unit 18 gives the alarm. As the maximum values of the time series signals in each of the plural frequency zones are extracted and compared, reliability of the determination is improved. |
