Working principle editing
By sequentially driving a red LED (660 nm) and an infrared LED (910 nm), the blue line indicates the hemoglobin-free oxygen molecule when the receiver tube reduces the hemoglobin induction curve. From the graph, the reduced hemoglobin to 660 nm red can be seen. The absorption of light is relatively strong, while the absorption length of infrared light at 910 nm is relatively weak. The red line indicates the hemoglobin-bearing red blood cell with oxygen molecules. The absorption curve of the oxygenated hemoglobin is shown in the figure. It can be seen from the figure that the absorption of red light at 660 nm is weak, and the absorption of infrared light at 910 nm is relatively strong. In the measurement of blood oxygenation, hemoglobin and oxyhemoglobin are reduced, and by detecting the difference in light absorption between two different wavelengths, the measured data difference is the most basic data for measuring blood oxygen saturation. In the blood oxygen test, the two most common wavelengths at 660nm and 910nm actually require higher precision, in addition to two wavelengths, even up to 8 wavelengths. The main reason is human hemoglobin in addition to reducing hemoglobin. In addition to oxyhemoglobin, there are other hemoglobins. We often see carboxyhemoglobin. More wavelengths will help you to do better precision.