Effect of characteristics of radiant signal on measured parameters of thermal spray particles

Using a single-window modulating aperture, a theoretical model for the evolution of radiant pulse signal is proposed, which is suitable for the measurement system based on thermal radiation to diagnose the velocity and the temperature of spray particles. According to the geometrical characteristics of signals, the four types of characteristic signals are defined. It is revealed that only the signal in curve-sided trapezoid shape with a saturated flat top can be used to measure reliably the parameters of spray particles such as velocity, temperature and size. The error in measured parameters of particles will be induced by the occurrence of other types of signals. The experiment results obtained using high velocity oxy-fuel spray process show that the measured signals present the characteristics predicted theoretically. The characteristics are significantly influenced by aiming distance and the diameter of aperture diaphragm. The decrease in the diameter of aperture diaphragm leads to the decrease in the measurement error of particle parameters, as well as in the amplitude of signal and the number of captured particles.