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.