Increasing the axial resolution of bore profile measurements made using acoustic pulse reflectometry

Li, A.; Sharp, D.B. and Forbes, B.J. (2005). Increasing the axial resolution of bore profile measurements made using acoustic pulse reflectometry. Measurement Science and Technology, 16(10) pp. 2011–2019.

DOI: https://doi.org/10.1088/0957-0233/16/10/017

Abstract

Acoustic pulse reflectometry is a useful non-invasive technique for measuring the internal dimensions of ducts. A sound pulse is injected via a source tube into the duct under test and the resultant reflections are recorded. Suitable analysis of the reflections then yields the input impulse response, from which the duct's bore profile can be calculated. The axial resolution of the bore profile reconstruction depends on the bandwidth of the signal used to probe the duct. The greater the high frequency content of the input signal, the higher the resolution of the reconstruction. In this paper, two methods of increasing the high frequency energy injected into the duct by the reflectometer are described. The first method involves supplementing the sound pulse measurement with bursts of high frequency sinusoidal pressure waves. The second method involves shortening the reflectometer source tube, thereby reducing the attenuation experienced by the input signal. Improved resolution bore reconstructions are presented which demonstrate the success of the two methods. Finally, the upper limit to the axial resolution that can be achieved, while still maintaining the accuracy of the calculated radius values, is discussed.

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