苏州普隆恩电子科技有限公司

苏州普隆恩电子科技有限公司

    苏州普隆恩电子科技有限公司           
    专业的电子元器件代理商        

基于LED-光电二极管的光学传感原理

关键词:NDIR,传感器,红外气体传感器点击:

Principle of Optical Sensing Based on LED-PD Optopair

Several measurement schemes can be used for optical sensing depending on the exact application and conditions.
根据具体应用和条件,可以使用多种测量方案进行光学传感。
 
 
1-channel measurement scheme
Basic measurement technique includes one LED and one photodiode. The LED emits radiation at a specific wavelength that corresponds to the absorption band of the analyte, the spectrally-matched photodiode detects it and puts out an electrical signal. Presence of the analyte in the environment between the LED and photodiode causes attenuation of the photodiode signal and, dased on the level of attenuation, it is possible to estimate the concentration of the analyte.

1通道测量方案
基本测量技术包括一个LED和一个光电二极管。 LED发射对应于分析物吸收带的特定波长的辐射,光谱匹配的光电二极管检测它并发出电信号。 在LED和光电二极管之间的环境中存在分析物导致光电二极管信号的衰减,并且基于衰减水平,可以估计分析物的浓度。


Advantages:
✔ allows designing low-cost solutions
✔ enables simple and compact sensor design
✔ provides decent results in normal conditions

优点:
✔允许设计低成本的解决方案
✔实现简单紧凑的传感器设计
✔在正常条件下提供不错的结果
This technique is used in most of our evaluation systems and sensor modules.
这种技术用于我们的大多数评估系统和传感器模块。
Influence of the temperature changing on the measured signal can be quite essential and may cause certain measurement error. There are several ways to consider this influence:
- use packages with built-in Peltier thermocooler and/or thermistor
- monitor intrinsic LED temperature judging by LED current-voltage dependence. Our standard electronics (D-51 LED driver and electronics used in on-board sensor modules) enables this option and puts out signals that carry information about the temperature changing. These signals can be used for the further arranging of the temperature compensation.

温度变化对测量信号的影响可能非常重要,可能会导致某些测量误差。 有几种方法可以考虑这种影响:
- 使用内置Peltier热电偶和/或热敏电阻的封装
- 通过LED电流 - 电压依赖性来监测固有的LED温度。 我们的标准电子设备(D-51 LED驱动器和车载传感器模块中使用的电子设备)支持此选项,并输出带有温度变化信息的信号。 这些信号可用于进一步安排温度补偿。
2-channel measurement scheme with 1 LED and 2 PDs (measuring and reference)
This scheme includes an additional PD apart from a measuring LED-PD optopair. The additional photodiode is a reference one and is introduced in order to compensate influence of irrelevant effects unrelated to the analyte absorption. Measuring photodiode provides the measuring signal sensitive to presence and concentration of analysed matter, while signal from reference PD remains practically unaffected. Processing of measuring and reference signals allows obtaining stable and reliable measurement results even in harsh temperature and environmental conditions thanks to the fact that photodiodes react in the same manner to the external conditions.

具有1个LED和2个PD的2通道测量方案(测量和参考)
除了测量LED-PD optopair外,该方案还包括一个额外的PD。 附加光电二极管是参考光电二极管并且被引入以便补偿与分析物吸收无关的无关效应的影响。 测量光电二极管提供对分析物质的存在和浓度敏感的测量信号,而来自参考PD的信号实际上保持不受影响。 由于光电二极管以相同的方式对外部条件作出反应,即使在恶劣的温度和环境条件下,测量和参考信号的处理也可以获得稳定和可靠的测量结果。
This scheme can be realised using 2 approaches:
a. reference PD has the same sensitivity spectrum as the measuring PD and is deposited close to the LED, thus ensuring the minimal signal attenuation due to short length of an optical path:

该方案可以使用两种方法实现:

a。 参考PD具有与测量PD相同的灵敏度谱,并且靠近LED沉积,从而确保由于光路长度短而导致的信号衰减最小:

b. reference PD has a spectrum insensitive to a given analyte and is deposited close to the measuring PD. This scheme should include an LED with a spectrum broad enough to provide the emission for two photodiodes with different wavelengths - measuring and reference or two similar photodiodes with additional optical filters to differentiate measuring and reference wavelengths.
b.参考PD具有对给定分析物不敏感的光谱,并且靠近测量PD沉积。 该方案应包括具有足够宽的光谱的LED,以提供具有不同波长的两个光电二极管的发射 - 测量和参考或两个类似的光电二极管以及用于区分测量和参考波长的附加光学滤波器。



2-channel measurement scheme with 2 LEDs (measuring and reference) and 1 PD 
2通道测量方案,带2个LED(测量和参考)和1个PD
This technique includes an additional LED apart from a measuring LED-PD optopair. Measuring LED emits radiation at wavelength corresponding to the maximum absorption of the analyte. Reference LED emits at wavelength that is not absorbed by the analyte. Signal difference between the measuring LED that is partially absorbed in the optical cell and the reference LED is proportional to the concentration of the analyte.
除了测量LED-PD optopair外,该技术还包括一个额外的LED。 测量LED以对应于分析物的最大吸收的波长发射辐射。 参考LED以未被分析物吸收的波长发射。 在光学单元中部分吸收的测量LED与参考LED之间的信号差异与分析物的浓度成比例。


2-channel measurement scheme with 2 LEDs (measuring and reference) and 2 PDs (measuring and reference)
2通道测量方案,带2个LED(测量和参考)和2个PD(测量和参考)
This approach is similar to the previous one with the only difference that additional photodiode is introduced for reference signal detection. The overall scheme includes 2 independent channels: measuring LED-PD optopair (corresponds to the absorption wavelength(s) of the analyte) and reference LED-PD optopair (operates at wavelength(s) away from the analyte absorption). Concentration of the analyte is defined by the signal difference between the measuring and reference PDs.
这种方法与前一种方法类似,唯一的区别是引入了额外的光电二极管用于参考信号检测。 整个方案包括2个独立通道:测量LED-PD optopair(对应于分析物的吸收波长)和参考LED-PD optopair(在远离分析物吸收的波长下操作)。 分析物的浓度由测量和参考PD之间的信号差异定义。


Common advantages of 2-channel schemes:
✔ enable compensation of the effects unrelated to the analyte absorption
✔ provide better stability of the measurement results comparing to the 1-channel scheme
✔ require less frequent calibration than systems based on 1-channel measurement scheme
双通道方案的共同优点:
✔能够补偿与分析物吸收无关的效应
✔与1通道方案相比,可提供更好的测量结果稳定性
✔比基于1通道测量方案的系统需要更少的校准


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