A METHOD FOR THE NONLINEAR APPROXIMATION OF COMPLEX SHAPED CONVERSION FUNCTIONS

Abstract

The aim of the study is to investigate the possibility of using the method and technique of piecewise nonlinear approximation for a highly accurate description (recognition) of the characteristics of the transformation of primary measuring devices (sensors), the transformation function (CF) of which has a rather complex form and a difficult to describe mathematical model. Materials and methods. The highly accurate description of this type of converter features provides for the division into nonlinear intervals over the entire measurement range. Each approximation interval forms a sequence falling between the extremum points of the considered CF and completely covers it. Besides, the third point between adjacent extremum points should be determined since it is the largest CF bending or turning point and allows expressing this approximation interval in the form of two different polynomials. Thus, each approximation interval is expressed in the form of two nonlinear functions – quadratic trinomials or cubic equations and is very close to the values of the real CF in this interval accurately describing the real CF. Results. The paper presents a developed hybrid test and structural measurement methods, as well as a relevant algorithm for implement¬ting these measurement procedures. Test measurement methods use simple additive and multiplicative tests, as well as combinations of these tests – hybrid test measurements. Errors are automatically corrected or compensated to ensure high measurement accuracy. Conclusion. Unlike the known approximation methods, this approach accurately identifies the current states of the primary measuring instrument of the FP ensuring automatic calibration, and most effectively – the drift of the FP. Measurements at any time period are made relative to the value in which the sensor conversion feature is determined, which significantly improves measurement accuracy due to the intelligent information and measuring system based on structural and algorithmic-test measurement methods and its intelligent information support.