针对激光粒度仪手动对中自动化程度低、不易调整等问题，提出了基于四象限对中单元的新型50通道光电探测器的自动对中方法。该方法根据光束是否处于四象限探测器的感光范围，将自动对中过程分为粗对中和精对中两部分。当光束不在四象限探测器的感光范围内时，可根据探测器的特定结构进行粗对中；当光束处于四象限探测器感光范围内时，根据四象限探测器产生的光电流强弱判断探测器的运动方向进行精对中。在粗对中过渡到精对中后采取变步长方式，通过比较对中精度和对中所需时间确定算法的最佳截止条件。完成了激光粒度仪自动对中系统硬件和软件的设计，实验验证了对中系统的可靠性与准确性。结果表明，最终的对中分辨率高于5 μm。使用该技术对标准颗粒样品进行了测量实验，结果证实自动对中后的测量数据符合国家激光粒度仪校准规范的要求。

As the manual centering of laser particle size analyzers is slow operation and difficult to be adjusted, this paper presents an automatic centering method for the 50-channel photo detector based on a four-quadrant detection unit. According to the different positions of the detectors, the process of automatic centering was divided into pre-centering and acute-centering. When the laser beam was out of the sensing range of the detector, the system carried out a pre-centering based on the special structure of the detector; When the laser beam could be sensed by the detector, the system undertook the acute-centering according to the photocurrent intensity from the detector to determine its motion direction. After transition from a pre-centering into the acute-centering, the variable step was used to obtain the best cut-off condition of the automatic centering system by comparing the centering accuracy and centering time. Furthermore, the designs of software and hardware of the laser size analyzer were completed and the reliability and accuracy of the system were verified. The results show that its resolution is higher than 5 μm. Finally, the method was used to test standard particles, and the data after automatic centering meet the requirements of calibration specification for static light scattering particle size analyzers.