Improved method for shot particle velocity measurement within a shotblasting chamber

This paper presents the application of two axially-spaced impact detecting sensors for correlation-based shot velocity measurement. The sensors were placed directly into the flow of shot particles for sensing the particles’ impact. The implementation of cross-correlation for phase shift determination, however, was not an easy task. Several extensive improvements were necessary, before the original measurement system, already presented in this journal in December 2003, was capable of reliable velocity measurements. This paper presents the development of the system and optimisation of its components. The construction of a sensor built from a small microphone encapsulated in a metal housing and placed under a protective shield was optimised for a high ratio of frontal to side impact signal alteration. High vibration damping was also necessary. It was achieved by the combination of a well-weighted design for supporting elements and by a careful selection of used materials. These measures improved the similarity of the signals generated by the particles’ impact, significantly, and allowed the use of cross-correlation. The accuracy of the obtained results increased drastically by the application of cross-correlation, signal filtering was unnecessary and the signal processing was much faster.