Patent ID: 7659512

Claim:
An oil type discrimination method, in which a sample, which is an oil to be discriminated from another, is irradiated with near infrared light and a type of oil of the sample is discriminated by measuring absorbance of a specific wavelength of the near infrared light, the method comprising: a spectrum measurement step of measuring a transmission spectrum of the near infrared light that has transmitted the sample; a spectrum conversion step of converting the transmission spectrum into an absorbance spectrum; a first discrimination step of finding a difference in absorbance between two wavelengths existing in the vicinities of respective attribute wavelengths of predetermined chemical bonds and discriminating whether the sample is gasoline type or non-gasoline type by comparing the difference in absorbance with a first reference value; a first derivative step of converting the absorbance into a first derivative spectrum when the sample is discriminated to be the gasoline type in the first discrimination step; a second discrimination step of discriminating whether the sample is regular gasoline or high-octane gasoline by comparing a value, which is obtained by multiplying respective first derivative values of absorbance of at least four wavelengths existing in the vicinities of the respective attribute wavelengths of the predetermined chemical bonds by respective coefficients, adding up products, and further adding a constant to a sum, with a second reference; and a third discrimination step of discriminating whether the sample is kerosene or diesel oil by finding the difference in absorbance between two wavelengths existing in the vicinities of the respective attribute wavelengths of the predetermined chemical bonds and comparing the difference in absorbance with a third reference value when the sample is discriminated to be the non-gasoline type in the first discrimination step.