Measurement of ultrasonic pulse velocity with improved accuracy using automatic threshold error correction

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.