Working principle of oximeter

The working principle of nail type oximeter: by driving a red LED (660nm) and an infrared LED (910nm) in turn, the blue line indicates the response curve of the receiving tube to the reduced hemoglobin when the hemoglobin does not carry oxygen molecules. From the curve, it can be seen that the absorption of reduced hemoglobin to 660nm red light is relatively strong, while the absorption length of 910nm infrared light is relatively weak. The red line indicates that when hemoglobin is mixed with red blood cells with oxygen molecules, the receiver has a weak absorption of 660nm red light and a strong absorption of 910nm infrared light. In the measurement of blood oxygen, reducing hemoglobin and oxygenated hemoglobin, by detecting the difference of light absorption of two different wavelengths, the measured data difference is the most basic data to measure blood oxygen saturation. In the blood oxygen test, the two most common wavelengths of 660 nm and 910 nm, in fact, need to achieve higher accuracy, in addition to two wavelengths, but also increase, even as high as 8 wavelengths. The main reason is that human hemoglobin has other hemoglobin besides reduced hemoglobin and oxygenated hemoglobin. We often see carboxyhemoglobin, More wavelengths will help you do better.