Abstract: The identification of a distribution law of the results of measurements of the composition and properties of petroleum products was carried out by testing a complex hypothesis using five goodness-of-fit tests: χ 2 -Pearson, Kolmogorov, Smirnov, ω 2 CramerMises-Smirnov; Ω 2 Anderson-Darling. Twelve symmetric unimodal distribution laws and 66 mixtures of the same distribution laws were considered as possible probability distribution functions. The purpose of the identification was to find a universal distribution law (a mixture of distribution laws) that is valid for all considered quantities. Testing the complex hypothesis of compliance with any symmetric unimodal distribution law showed that there is no universal distribution law that is valid for all measurement techniques of the composition and properties of petroleum products; most often the hypothesis of the correspondence the data to the generalized logistic distribution, the Laplace distribution and the two-sided exponential distribution was not rejected. Testing a complex hypothesis about the correspondence of any mixture of symmetric unimodal distribution laws showed that the empirical distribution function of the results of measurements of the composition and properties of petroleum products can be represented as a mixture of two normal distributions with different values of the position and scale parameters. At the same time, for the same sample, the values of the achieved significance level of the hypothesis about the correspondence to the mixture of distribution laws is several times higher than the average value of the achieved significance level of the hypothesis about the correspondence to one distribution law. Based on this study, a chance model of the process of testing petroleum products was substantiated, within which the result of testing petroleum products is considered as a random variable with a distribution function in the form of a mixture of normal distribution laws: "basic" with a variance not exceeding the established requirements (with a statistically controlled state of the test process), and "fouling" with a variance significantly exceeding the established requirements (with a statistically uncontrolled state of the test process).
Index terms: petroleum products, measurements of composition and properties, distribution law, identification, goodness of fit of a distribution, chance model.

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