Features of the study of condensed matter using the nuclear magnetic resonance method based on relaxation times $T_1$ and $T_2$

The features of determining the longitudinal $T_1$ and transverse $T_2$ relaxation times in NMR relaxometer designs for measuring the parameters of condensed matter for various applications, including biology and medicine, which are both in a stationary and current state, are considered. The advantages of using the modulation technique for recording the NMR signal for flow NMR flowmeters-relaxometers and small-sized NMR relaxometers for express monitoring of condensed matter in comparison with other methods and techniques are noted. It has been experimentally proven that the resulting relationship from the Bloch equations using approximations for determining $T_1$ from the results of two measurements of NMR signal amplitudes or resonant frequencies has a number of restrictions on application for both flowing and stationary condensed matter. These limitations are associated both with the technique of recording the NMR signal and with the ability to generate NMR signals for different modulation frequencies of the H0 field, the amplitudes of which will differ from each other beyond the measurement error. The reasons that led to this discrepancy in the ratio for determining $T_1$ and the limits of applicability of this ratio are determined. Based on experimental data, a study of the relationship for determining $T_1$ was carried out and it was proven that for a number of cases using it is impossible to obtain the $T_1$ value. In this case, NMR signals from a condensed medium are recorded in these cases, and the medium itself has relaxation times $T_1$ and $T_2$. The results we obtained make it possible to eliminate errors when conducting experiments when studying condensed matter using the NMR method, this is especially important in biology and medicine, where the requirements for measurement accuracy are increased.