分析了消光式液体颗粒计数传感器的典型结构,并根据Mie理论计算了折射率为1.33的消光系数曲线,说明颗粒粒径在小于2 μm时与消光系数呈多值性对应关系,指出这种多值性关系是影响此类计数器不能用于检测小颗粒的主要原因。最后提出一种改进的液体颗粒计数传感器结构,对传感器中光学部分的采光透镜组进行了改造,增加散射光探测器和光源监控探测器。通过计算说明了将散射光探测器安置在45°采光角时的原因,此时的光能与颗粒粒径之间有较好的单值对应关系,还可减少折射率对测量结果的影响。实验对比表明,改进结构的传感器对小于2 μm的标准颗粒试样有较好的检测能力,而且多次重复测量结果相近;对大于2 μm颗粒的检测能力仍然保持着较高的水平。

Particle counter of extinction type is used mainly to detect the particulate contamination of larger sizes, and widely applied in contamination control measurement and monitor, whereas it is unable to detect smaller sizes particulate, the reason is discussed in this paper. Based on Mie theory, extinction coefficient is calculated, at the same time, the representative structure of this type sensor is analyzed. Numerous calculation and analysis showed that it is due to the ambiguity relationship of extinction coefficient versus particulate sizes less than 2 μm and unreasonable design. An improved design of the sensor was proposed, which employs a specially designed detecting lens unit to collect more scattered light and a monitoring device to control the light source, the lens of collecting scattering light is arranged at 45 degree, which can lead the good monodromy for light energy versus particulate sizes and less interference due to particle refractive index. Comparative experiments showed that the lower limit of the measuring size range could be extended by the new sensor design. The new sensor has a good detect ability for particle sizes less than 2 μm and lower repetition errors, and furthermore, it still has a high level for detecting larger sizes particle, it suits for more application of contamination degree monitoring.