Method of liquid consumption measurement in nuclear magnetic resonance flowmeters-relaxometers

The need to expand the functionality of systems for monitoring the parameters of the flow of liquid media is substantiated. This article presents the advantages of using meters based on nuclear magnetic resonance (NMR) to control the parameters of the flow of liquid media. This paper also aims to solve the problems that arise during the operation of NMR flowmeters-relaxometers in two measurement modes (i.e., pulse mode and mode with periodic modulation of the magnetic field in the NMR signal recording system). Notably, the main problem in the operation of these devices is associated with an increase in the error in measuring liquid flow or the termination of its measurement process with rapid changes in liquid flow. The use of a magnetic mark mode, which helps solve the aforementioned problem, significantly limits the possibilities of using NMR flowmeters-relaxometers when used to monitor the parameters of liquid media or with a large increase in the flowing medium temperature. A method for creating a magnetic mark at the noise level for measuring liquid flow is proposed. In this method, changing the composition of the flowing medium or replacing the liquid does not have a significant effect on the formation of a magnetic mark at the noise level in a strong inhomogeneous magnetic field (i.e., the noise amplitude is several times higher than the signal amplitude). The results of experimental studies of the nutation line from changes in the magnetic field gradient are presented. A mathematical model based on the modified Bloch equations is developed, and the relationships between the magnetic field parameters are established to implement the magnetic mark mode in the NMR signal with magnetization inversion at the noise level. The proposed method ensures that the influence of rapid changes in the value of liquid flow (by a factor of 10 or more) on the flow measurement error is insignificant.