Method for operating a nuclear magnetic flowmeter

Method for operating a nuclear magnetic flowmeter for determining the flow of a multi-phase medium flowing through a measuring tube, having a pre-magnetization unit for pre-magnetization of the medium, a magnetic field generator for generating a magnetic field interfusing the medium and a measuring device that includes at least one coil-shaped antenna for generating excitation signals exciting the medium and/or for detecting measuring signals emitted by the medium, comprising the steps of:

• emitting a pulse spoiling the magnetization at least in the direction of the magnetic field or a pulse sequence spoiling the magnetization in the direction of the magnetic field by the coil-shaped antenna,
• waiting a waiting time tw, and
• then, carrying out a nuclear magnetic measurement by exciting the medium with excitation pulses by the coil-shaped antenna and by detecting measuring signals generated by the excitation of the medium,
• wherein the waiting time tw is determined in accordance with the relationship
• t
• W
• ≥
• L
• 1
• v
• gas
• wherein L1 is the length of the coil-shaped antenna and vgas is the flow velocity of the gaseous phase;
• wherein the waiting time tw is iteratively determined using the signal amplitude and the signal amplitude Sgas of the gaseous phase, wherein the signal amplitude ratio and the signal amplitude of the gaseous phase are at a maximum for
• t
• W
• =
• L
• 1
• v
• gas
• ,
• and
• wherein flow velocities of individual phases are determined using the measured values obtained by the nuclear magnetic measurements.