Three-wavelength Oxygen Saturation Measurement Instrument Developed

Oxygen is the key material to human's life, and oxygen saturation is one of the important indexes reflecting organic oxgen delivery status. Conventional two-wavelength pulse oximeter is accurate at high oxygen satuation under a variety of physiological conditions, but show worsening accuracy at lower saturation . The principle and technique of the oximeter,the Lamber-Beer Law and the difference in optical absorbencies of the components in tissues related to different light wavelength, employed in transmittance oxymetry are analyzed in order to accurately measure lower saturation of the futus, the infant and the patients in intensive care.The overseas research result about the optimal selection of wavelength for low saturation pulse oximeter are adopted.The stable accuracy of the pulse oximeter occurs when the fractional change in photon paths due to perturbations in the tissue is equivalent at the two wavelengths .Additionally, the penetration depth of the probing light needs to be well matched at the two-wavelength in order to minimize the effects of tissue heterogeneity.At low saturation, it is better using 735 and 890nm wavelength than that using 660 and 940nm wavelength. Three -wavelengths pulse oximeter based 51micprocessor is developed for the sake of improving low-saturation precision and a new arithmetic is brought forth. This paper also includes the software and hardware design and implemention of the three –wavelength pulse oximeter. At last ,a variety of factors affecting measure precision are analyzed and the means of eliminating interferential signals are presented.