Chromatic Monitoring of DC Plasma Torches: The Latest Developments

摘要

The chromatic-sensing technique is based on reduction of the optical spectroscopic information about an object to three signals obtained by photodetectors with different spectroscopic responsivities. Each plasma state is represented by a point of the hue, luminance, and saturation (HLS) or C_1C_2C_3 chromaticity space. For specific operating conditions, the plasma fluctuations cause the formation of a ring around the point of S = 0, which makes the measurement of H impossible. Such a situation can be avoided by alternative tuning of the chromatic system. Systematic studies of the output/input correlation for air and water vapour/argon mixture plasmas are made. The results are presented in the form of 'response surfaces', which are of interest for an eventual on-line control. This is illustrated by a 'C_2 vs. argon flow rate and jet axial co-ordinate' surface, which can be used to locate the correct powder injection point in a plasma spray process.