RESUMO
Ultrasonic Pulse Velocity (UPV) measurement is extensively used to monitor the strength and health of concrete structures as per American Society for Testing and Materials C 597 - 09. The commercially available UPV measurement systems work on the basis of single threshold detection of the received signal. Therefore, measurement accuracy is affected due to threshold error. The effect is sensitive to the signal amplitude reaching the threshold comparator and, hence, receiver gain. It is observed that a UPV tester operating at 50 kHz to test concrete might generate an error of up to 10% in the ultrasonic transit time measurement of 50 µs. Hence, it is of great concern and needs to be improved. In this article, the UPV measurement circuit capable of detecting and compensating the threshold error is described. The threshold error correction is achieved with the help of two threshold comparators and two hybrid counters. The circuit developed minimizes the threshold error for wide receiver gain. The measurement carried out with the developed system shows significant improvement, having deviations within 100 ns.
RESUMO
An ultrasonic interferometer with variable separation between the transducer and reflector is widely used for the measurement of ultrasonic propagation velocity in liquids. The inherent limitation of such an interferometer is due to the mechanical movement of its reflector for ultrasonic wavelength measurement in a liquid medium. It is observed that the ultrasonic velocity measurement precision is adversely affected at higher frequencies compared to lower ones. For instance, in our experimentation, a standard deviation of ±21.5 m/s (±1.43%) was obtained for velocity measurement at 1.84 MHz with the consideration of two consecutive maxima, which increases drastically to ±76.8 m/s (±5.12%) at 9.4 MHz. These measurements can significantly be improved by considering many maxima and averaging for wavelength estimation. However, it still requires design attention and improvement, particularly for higher frequencies. In this article, a sweep-frequency based ultrasonic interferometer design with a fixed separation for liquid characterization is proposed and described. This technique overcomes the limitations of mechanical movement systems and also provides a better and uniform precision for lower as well as higher frequencies. The functionality of the developed sweep frequency method was tested in water, carbon tetrachloride, ethylene glycol, and glycerol, which shows good agreement with literature values. The velocity measurement in double distilled water by the developed technique at 1 Hz sweep resolution has shown an improved standard deviation of ±0.74 m/s (±0.05%) at 9.4 MHz.
