Methods of measuring delay time between periodic sequences of pulses are mostly based on the considered parameter direct measurement. The main disadvantage of this approach is the difficulty of ensuring the measurements accuracy in the noise conditions. The aim of this work was to develop a method that provides the ability to accurately measure small changes in time intervals, based on the analysis of the dynamic properties of the spectrum of the delayed measurement signals sum.The developed method essence is to replace the insensitive registration of changes in the delay time between periodic pulses sequences, registration of changes in the parameters of the characteristic harmonic components of the spectrum of the resulting sum of these signals. In this case, only those harmonic components were taken into consideration that have a maximum sensitivity to delay time deviations and a minimum sensitivity to uncorrelated signal parameters changes.To achieve the maximum effect, the influence of the pulse shape of periodic sequences on the measurement accuracy was investigated. Moreover, the trapezoidal form of impulses was taken as the basic as the most common, into which all other forms of impulses can be reborn (triangular, rectangular, sinusoidal, etc.).The calculation results showed the effectiveness of the proposed method in order to reduce the measurement error of small changes in time intervals. In this case, the attenuation error coefficient compared with the existing measurement method amounted to Kwe = 4,78. Using the proposed approach opens up the possibility of improving the algorithmic support of measuring instruments in order to automate them and increase the measurements accuracy.

The solution of problems of diagnostics of windings of electric machines is associated with the necessity of selection of quasi-periodic test signals against the background noise. In order to highlight useful signals, as a rule, the differences in spectral compositions of signals and noises are used. Ideally, the shape of the optimal filter frequency response should coincide with the shape of the spectrum of the useful signal, which determines the complexity of such a filter. The aim of the research is to increase the accuracy of measurements and simplify the algorithmic support of measuring systems by developing a mathematical tool that makes it possible to uniquely identify and take into account errors caused by the finiteness of the measurement intervals in the processing. Determining a one-to-one relationship between local variations of signal time parameters and alterations in its spectrum parameters is believed to be the reserve of increase of sensitivity of methods of processing of quasi-periodic signals in the conditions of constant growth of computing capabilities of measuring instruments. Variations in the values of the parameters of the signals lead to a violation of the original distribution of the harmonic components, some of the latter being subjected to the greatest alterations changes, and the some other – to the smallest ones. It is proposed to increase the accuracy of measurements due to the replacement the low-sensitivity registration of alterations in the time parameters of signals with the registration of alterations in the parameters of the characteristic harmonic components of the spectrum, which have a maximum sensitivity to deviations of the controlled parameter and a minimum sensitivity to deviations caused by the instability of the measuring equipment. The mathematical tool corresponding to the practice has been developed, that makes it possible to determine unambiguously the errors caused by finiteness of measurement intervals of quasi-periodic signals. Automatic accounting of these errors makes it possible to do without complex correlation processing of quasi-periodic signals that require large computing resources (time and speed of data processing, the amount of RAM) and to ensure the accuracy of measurements.