Li Qing-Bo, Xu Yu-Po, Zhang Chao-Hang, Zhang Guang-Jun, Wu Jin-Guang
Key Laboratory of Precision Opto-mechatronics Technology, Ministry of Education, College of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2009 Oct;29(10):2875-8.
A portable nondestructive measuring instrument for plant chlorophyll was developed, which can perform real-time, quick and nondestructive measurement of chlorophyll. The instrument is mainly composed of four parts, including leaves clamp, driving circuit of light source, photoelectric detection and signal conditioning circuit and micro-control system. A new scheme of light source driving was proposed, which can not only achieve constant current, but also control the current by digital signal. The driving current can be changed depending on different light source and measurement situation by actual operation, which resolves the matching problem of output intensity of light source and input range of photoelectric detector. In addition, an integrative leaves clamp was designed, which simplified the optical structure, enhanced the stability of apparatus, decreased the loss of incident light and improved the signal-to-noise ratio and precision. The photoelectric detection and signal conditioning circuit achieve the conversion between optical signal and electrical signal, and make the electrical signal meet the requirement of AD conversion, and the photo detector is S1133-14 of Hamamatsu Company, with a high detection precision. The micro-control system mainly achieves control function, dealing with data, data storage and so on. As the most important component, microprocessor MSP430F149 of TI Company has many advantages, such as high processing speed, low power, high stability and so on. And it has an in-built 12 bit AD converter, so the data-acquisition circuit is simpler. MSP430F149 is suitable for portable instrument. In the calibration experiment of the instrument, the standard value was measured by chlorophyll meter SPAD-502, multiple linear calibration models were built, and the instrument performance was evaluated. The correlation coefficient between chlorophyll prediction value and standard value is 0.97, and the root mean square error of prediction is about 1.3 SPAD. In the evaluation experiment of the instrument repeatability, the root mean square error is 0.1 SPAD. Results of the calibration experiment show that the instrument has high measuring precision and high stability.
研制了一种便携式植物叶绿素无损测量仪，可对叶绿素进行实时、快速、无损测量。该仪器主要由四部分组成，包括叶片夹、光源驱动电路、光电检测与信号调理电路以及微控制系统。提出了一种新的光源驱动方案，不仅能实现恒流，还能通过数字信号控制电流。通过实际操作，驱动电流可根据不同光源和测量情况进行改变，解决了光源输出强度与光电探测器输入范围的匹配问题。此外，设计了一体化叶片夹，简化了光学结构，增强了仪器稳定性，减少了入射光损失，提高了信噪比和精度。光电检测与信号调理电路实现光信号与电信号的转换，使电信号满足模数转换要求，光电探测器采用滨松公司的S1133 - 14，检测精度高。微控制系统主要实现控制功能、数据处理、数据存储等。作为最重要的部件，德州仪器公司的微处理器MSP430F149具有处理速度快、功耗低、稳定性高等诸多优点。且其内置12位模数转换器，使数据采集电路更简单。MSP430F149适用于便携式仪器。在仪器校准实验中，用叶绿素仪SPAD - 502测量标准值，建立多元线性校准模型，并对仪器性能进行评估。叶绿素预测值与标准值的相关系数为0.97，预测均方根误差约为1.3 SPAD。在仪器重复性评估实验中，均方根误差为0.1 SPAD。校准实验结果表明该仪器具有较高的测量精度和稳定性。
