The Blood Oxygen Photoelectric Detection Using Dual Wavelength Light Sources

The oximeter is getting more and more popular, and it brings convenience to people’s life. However, some factors such as the noise in different environment and testers’activities affect the accuracy of the oximeter. To obtain more accurate and reliable signal, the question of improving its precision and restraining disturbance is still worth to discuss.In this paper, a set of self-made pulse blood oxygen measurement system is introduced, the hardware circuit design and software processing system of blood oxygen detection are completed, which greatly reduces the disturbance of external noise and improve the accuracy of the signal.Through the study on the optical properties of the tissue of human and analyzing the relationship between pulse wave and deoxygenated hemoglobin, oxygen oxyhemoglobin with the Lambert-Beer law and its modified formula, a blood oxygen saturation formula was obtained. According to the absorption characteristics of the human body tissue in the near infrared, the wavelength of 780nm and 830nm were selected as the detection light wavelength, and the semiconductor laser with better monochromatic light was used as the light source.To design and optimize the system, a scheme that the pulse wave signal obtained by using sine wave drive and coherent demodulation dealt by computer technology is proposed. In circuit part, the stability of the circuit and the accuracy of the acquisition process are improved. For the influence of noise signal in the circuit, two-order filter and high-order filter circuit are used to filter it. Several signal denoising processing methods are discussed. According to the signal and noise’s different forms and presences in wavelet domain, the method of signal processing and calculation based on wavelet transform and FFT can reduce noises in different frequency bands to obtain the oxygen saturation value.Oxyhemoglobin saturation measurement on a number of people was carried out with this system, and the results were compared with those measured by instruments on the market, the error is very small, which verifies the accuracy and effectiveness of the measuring system.