CHARACTERIZATION OF THE BEHAVIOUR OF A PLASMA TORCH BY ELECTRIC, ACOUSTIC AND LUMINOSITY MEASUREMENTS

Voltage, current, acoustic pressure and light fluctuations from a plasma torch were recorded and analysed by fast Fourier transform (FFT). These measurements were performed for three nozzle diameters, and varying the argon plasma gas flow rate up to 30 l/min. At high flow rates the results confirm the observations depicted in the litterature concerning the good correlation between these different signals. At low gas flow rate a peak in the acoustic pressure spectra which maximum intensity coincide with the laminar-turbulent transition could be used to characterize this transition.