Study On Adaptive Real-time Correction Algorithm For External Stray Light Of Spectrophotometer

As one of the instruments commonly used for quantitative analysis of substances,spectrophotometer will be interfered by external stray light to varying degrees in the process of instrument analysis.Existing spectrophotometers usually correct stray light just during it's system initialization,and it cannot correct the stray light value in real time according to external stray light,resulting in errors in the measurement.Especially in the field or outdoors online detection,stray light time-varying characteristics are obvious,traditional calibration methods can no longer meet the needs of spectrophotometer in measurement accuracy and rapid deployment in the outside.In order to improve the anti-stray light interference ability of the spectrophotometer,this paper proposed a real-time correction method for external stray light that combines Pulse Width Modulation(PWM)and Least Mean Square(LMS)adaptive filtering technology.The light source signal is modulated by PWM technology,and the reference signal and original signal with stray light are acquired by time division.By adaptive predictor of the reference signal,the external stray light in the original signal is estimated.Finally,the real-time correction of the external stray light in the original signal can be realized by the adaptive noise canceller(ANC).The simulation results show that the proposed method can suppress the external stray light in the original signal and keep the relative error between the expected value and the final output intensity within 0.15%.In addition,an automatic adjustment strategy of light source intensity is proposed in order to ensure the spectrophotometer can work normally under the strong external stray light interference.On the basis of obtaining the reference signal of the external stray light,the optimal adjustment range of the light source intensity is obtained by analyzing the variation range of the external stray light and the constraint condition that the spectrophotometer can work normally.Finally,the optimal light intensity of the light source is obtained according to the maximum signal-to-noise ratio criterion.The simulation results show that the automatic adjustment strategy of light source intensity can achieve the optimal adjustment of light source intensity within constraints.In order to further verify the validity of the method,this paper builds a set of portable outdoors spectrophotometer system.This method use single chip microcomputer to produce PWM signal for constant current modulation of the light source,and to control adjustment by changing the drive current.By 16 bits of data acquisition card to realize acquisition and transmission of the photoelectric detector output signal,this adopts correction algorithm for data processing and display the results in the upper machine.The results of measurement and analysis of the standard phosphate solution under different external stray light disturbances show that the system loaded with correction algorithm improves the R-squared(R2)of the standard curve from 0.99 to more than 0.999,and when the external stray light changes in real time,the relative error of the measured value of the light intensity is within 0.23%.Compared with the mature commercial instruments under the same experimental conditions,the results show that the system loaded with correction algorithm has excellent performance,which can achieve the standard for the determination of unknown solution concentration,and meet the ability of rapid deployment in the outside The method proposed in this paper is simple,efficient and easy to implement,which improves the measurement accuracy and stability of spectrophotometer and has better practicability and popularization.