This paper is concerned with the development of an instrument capable of measuring the concentration of, and fluctuations in suspended abrasive particles in high pressure abrasive suspension jet, ASJ, cutting systems, facilitating for the first time the investigation into effects of fluctuations in concentration on cut surface finish. Due to the highly abrasive and high pressure of the slurry in a suspension jet system a non-intrusive measurement method was needed. A theoretical study of the attenuation of ultrasound in suspensons showed that if two frequencies are used and independent pressure and temperatures measuremnets made, a device could be developed that automatically accounts for changes in particle size and fluid based parameter changes. Thus such a system culd be applied to any suspension jet system regardless of abrasive size or pressure. A laboratory model of a field instrument was constructed, and tests were performed on a range of suspended sediments with differing mean particle sizes and pressures, and shown to give concentration predictions to an accuracy better than 2percent on slurries at pressures up to 69MN/m~2. For the first time concentration and concentration fluctuations in ASJ systems can be monitored at a high frequency and resolution during the cutting process, enabling for the first time the observation of short duration abrasive fluctuations and facilitation the investigation into their effect on cut surface finish.
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