Measuring and testing – Vibration – By mechanical waves
Patent
1998-12-31
2000-12-26
Williams, Hezron
Measuring and testing
Vibration
By mechanical waves
73579, G01N 2912
Patent
active
061641367
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for the investigation of boundary layer areas using ultrasound with at least one transmitting unit with which transmission signals of adjustable amplitudes with at least one fundamental frequency can be generated, with a receiver unit with which the at least one fundamental frequency as well as at least the associated lowest of the higher harmonics of the at least one fundamental frequency of the transmission signal can be detected in their frequency amplitudes as reception signals, and with an analysis unit in which the frequency amplitudes of the reception signals can be joined into a measured value.
A device of this type is known from German Patent No. 43 24 143 C1. In this device, a transmission unit is provided with which at a fundamental frequency, transmission signals of adjustable amplitude can be generated. With a receiver unit, frequency components at the fundamental frequency as well as higher harmonics of the fundamental frequency can be detected. A characterization of boundary layer areas with respect to cohesive force relationships in a boundary layer area being investigated is created through the frequency amplitudes of the fundamental frequency as well as at least one additional frequency amplitude at an additional frequency component which is related harmonically to the fundamental frequency are summed. In order to achieve physically correct relative measured values for characterizing the cohesive force potential, the frequency components at harmonics with an even ordinal number are to be weighted negatively and the harmonics with an uneven ordinal number are to be weighted positively. In addition, in order to correctly characterize the cohesive force potential in absolute terms as well, it is necessary to determine a direct current component.
While it is true that the cohesive force relationships can be characterized with the generic device it nevertheless has the disadvantage that the direct current component, by way of example, is technologically difficult to measure. In addition, quantitative statements with respect to the also important adhesive strength, i.e., the difference from maximum cohesive strength, is not possible.
The objective of the invention is to further develop a device of the type referred to at the beginning with which a precise, trouble-free determination of adhesive strength is created with low technological expenditure.
This objective is achieved according to the invention by the measured value having the simple frequency amplitude of a fundamental frequency and at least double the negative value of the frequency amplitude of the lowest of the higher harmonics associated with this fundamental frequency.
As a result of the measured value being composed of the simple frequency amplitude of the at least one fundamental frequency as well as at least double the negative value of the frequency amplitude of the associated lowest of the higher harmonics, i e., the second harmonic at double the fundamental frequency, quantitative statements on adhesive strength can be made which are relatively simple and free of interference. Determination of a direct current component is not necessary even for quantitatively correct adhesive force measured values.
In advantageous further developments, along with the second harmonic, also additional higher harmonics are measured. An increase in measuring precision, is achieved by this means. The frequency amplitudes of the third and fifth harmonics with respectively three times and five times the fundamental frequency are taken as simple positive values and that of the sixth harmonic with its sixfold fundamental frequency is taken as a double negative value. In this process, the fourth harmonic with the fourfold value of the fundamental frequency must be left out of consideration.
Accordingly, frequency components with the value of (2n+1) times the fundamental frequency must be taken with a weight of one and those with the value of 2(2n+1) must be taken as a double negative value, whereby "n" represents a who
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Fassbender Silvia
Hirsekorn Sigrun
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Miller Rose M.
Williams Hezron
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