光学组件参数对热喷涂粒子参数测量的影响

Effect of Optical Component Parameters on Signal Characteristics and Measured Parameters of Thermal Spray Particles

为保证热辐射法测量热喷涂粒子参数的精度,分析了主要光学参数对信号强度和特征的影响,并通过用等离子喷涂纯Mo粉末进行了实测验证.结果发现:信号强度主要由孔径光阑直径和瞄准距离决定,而信号特征则随粒子空间分布、孔径光阑直径及调制窗口尺寸的变化而改变;试验证实实测信号的相对强度和信号特征与预测规律基本吻合.大直径孔径光阑在提高信号强度和信噪比的同时导致信号特征恶化,小直径孔径光阑有利于获得特征良好的信号,但也会导致信号强度、信噪比和测量结果集中程度的降低.因此,在系统设计过程中,应在采用直径尽可能小的孔径光阑保证粒子信号特征的前提下,引入雪崩光电二极管等高灵敏度器件来提高系统的光电灵敏度,确保信号强度和信噪比,进一步提高测量精度.

The effect of the optical components on the voltage level and the characteristics of thermal radiation signals was analyzed to ensure the accurate measurement of the parameters of the thermal spray particles. An experiment was carried out with air plasma sprayed Mo powder. It is found that the voltage level of signal pulses is determined by the aperture diameter and the aiming distance for the specific materials. The radiant signal characteristics vary with the spatial position of particles, the aperture diameter, and the dimension of the modulating window. The relative theoretical voltage level and the theoretical signal characteristics agree well with the experimental results. It is obvious that the large aperture leads to increasing signal to noise (S/N) ratio and worsens signal characteristics. While the small aperture contributes to the formation of well-shaped signals and results in decreasing S/N ratio and larger deviation of measurement data. Consequently, the aperture diameter ought to be selected as small as possible in the system design to ensure the generation of pulse signal with fine characteristic pattern, and the opto-electronic sensitivity of the system be adjusted high enough to ensure sufficient amplitude and S/N ratio of signals. Thus, it is necessary to introduce the photo sensor with higher sensitivity, such as avalanche photo diode (APD), to increase the measurement accuracy.