采用一套光电转换系统并增加一个正交信号发生器,设计了正交相关的双光束分光光度计.光电转换系统包括一个光电二极管、一个信号滤波放大和一个AD转换;正交信号发生器是一个部分直通的旋转圆盘,每一个周期它将参考信号和样品信号以正交相关的编码形式同时投射到光电转换系统上,转换得到的复合信号除了参考信号和样品信号,还包括光电二极管的暗电流信号.主控制系统按照三个信号各自的编码将它们分别分离并还原出来供后续分析计算用.由于正交相关的双光束分光光度计只采用一套光电转换系统且正交信号发生器每一个旋转周期都可以检测参考信号、样品信号、暗电流信号,避免了由于转换器件个体差异和检测时间的不同而产生的测量误差.实验验证了正交相关的双光束分光光度计在稳定性和测量精度上具有一定的优势.

To reduce the test error,the orthogonal double beam spectrophotometer was designed. The orthogonal double beam spectrophotometer uses one photoelectric conversion system which includes one photodiode,one filtration and amplification,one AD conversion and adds a producer of orthogonal signal which is a rotatable disk and non-opaque somewhere. In each cycle the reference signal and sample signal get through the producer of orthogonal signal and project to the photoelectric conversion system. In this way,the signals collected by the photoelectric conversion system in each cycle are composite and consist of the reference signal,sample signal and dark current signal,each of which will be separated by the master control system of FPGA as each code and restored for the following calculation and analysis. Since the error caused by the differences of photoelectric transducer and collecting time is avoided theoretically,the measurement accuracy of double beam spectrophotometer can be improved through taking one photoelectric conversion system and adding a producer of orthogonal signal. The experimental results show that the orthogonal double beam spectrophotometer has advantages in stability and accuracy.