transmitting respective acoustic waves to a plurality of reference objects having respective front surfaces with respective layers thereon, the layers of the reference objects being of a same type as the layer of the test object and having respective known mutually different thicknesses;
receiving respective acoustic waves from the reference objects, the acoustic waves received from the reference objects having been produced by the acoustic waves transmitted to the reference objects and being one of
(1) reflected acoustic waves which have passed through the reference objects and have been reflected from respective back surfaces of the reference objects at least once, and
(2) transmitted acoustic waves which have passed through the reference objects at least once;
determining respective frequency spectrums of the acoustic waves received from the reference objects;
determining respective centers-of-frequency of the frequency spectrums of the acoustic waves received from the reference objects;
determining a thickness function defining a relationship between the centers-of-frequency of the frequency spectrums of the acoustic waves received from the reference objects and the thicknesses of the layers of the reference objects;
transmitting an acoustic wave to the test object;
receiving an acoustic wave from the test object, the acoustic wave received from the test object having been produced by the acoustic wave transmitted to the test object and being one of
(1) a reflected acoustic wave which has passed through the test object and has been reflected from a back surface of the test object at least once, and
(2) a transmitted acoustic wave which has passed through the test object at least once;
determining a frequency spectrum of the acoustic wave received from the test object;
determining a center-of-frequency of the frequency spectrum of the acoustic wave received from the test object; and
determining the thickness of the layer of the test object from the thickness function based on the center-of-frequency of the frequency spectrum of the acoustic wave received from the test object.
Abstract: Ultrasonic waves from a transmit device are transmitted to an object subject to measurement. A surface reflected wave propagated in a contact medium and reflected at the surface of a tube and bottom surface reflected waves passing through an oxidation layer on the tube and reflected at the inner surface of the tube are convened into electric signals. A feature extracting part 5, in consideration of a correlation relationship of energy with respect to the frequency of a received signal, based on the received signal of ultrasonic waves converted to electric signals, extracts a signal feature data determined beforehand which has a strong correlation relationship with the thickness of a measured part. Based on the extracted signal feature data, a thickness conversion part references a relationship storage part which has stored therein beforehand a function that shows a relationship between the signal feature data and the thickness of the oxidation layer, and obtains the thickness of the oxidation layer.
U.S. Class: (73/599) (73/602) (364/507)
IPC: (G01N 29/08) (G01N 29/10)
US Patents Cited: 4305294 4452082 4539847 4625556 4646748 4648276 5271274 5305239 5351544 5408881 5426979
Priority: (JPX 19941018 6-251784)
OG Section: Electrical
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