Application of zero-phase digital filter in ultrasonic pressure measurement

Conventional methods for pressure measurement commonly require drilling a hole in the wall of the vessels, which usually lead to potential safety problems. It is meaningful to study a nondestructive pressure measurement method using ultrasonic technique. One of key problems in ultrasonic pressure measurement is to estimate the time delay of two ultrasonic pulses accurately. A general cross correlation method based on zero-phase digital filter was presented to improve the accuracy of time delay estimation. Ultrasonic critically refracted longitudinal wave was applied to measure the pressure. Ultrasonic signals contain the correlative noise, therefore, pre-filtering of signal was needed. Zero-phase digital filter which could effectively eliminate the phase distortion that caused by common digital filter was proposed to process the signals. Compared to Hilbert-Huang Transform, the experimental result shows that the general cross correlation method based on zero-phase digital filter is more stable and simpler.