| 摘要 |
PCT No. PCT/EP82/00069 Sec. 371 Date Dec. 1, 1982 Sec. 102(e) Date Dec. 1, 1982 PCT Filed Mar. 29, 1982 PCT Pub. No. WO82/03455 PCT Pub. Date Oct. 14, 1982.In a method of controlling or measuring layer thicknesses, wherein a continuous frequency-modulated ultrasonic signal that periodically scans a frequency band is transmitted and wherein the resultant signal is evaluated. The frequency bandwidth is selected large enough that a multiple of the interference interval is covered. The spectral maxima or minima which periodically recur in the frequency spectrum of the received signal are evaluated. At a fixed modulation rate of the transmitted signal, an unambiguous interrelation exists between the repetition frequency of the maxima or minima in the spectrum and the thickness of the layer under examination. The repetition frequency increases with increasing layer thickness. According to an alternative embodiment of the invention, a ratio of harmonic amplitudes corresponding to the layer thickness is evaluated. The harmonics are produced by selecting a narrow frequency band, so that only part of the interference interval is covered. The repetition frequency of modulation is determined as a function of the desired measuring range.
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