Abstract: A method and apparatus are set forth for measuring flow velocity of an element of interest in a compound within a pipe. In the preferred and illustrated embodiment, a static magnetic field is imposed on the flowing material of interest. Preferably, a uniform field of finite width is imposed. There is a first coil around the path for imposing an RF magnetic field at right angles to the static magnetic field. There is a relationship between the flowing material including the element, frequency of the RF field and static magnetic field intensity which aligns nuclei or electrons of the element. There is a second (detection) coil spaced downstream from the first coil, the second coil also being around the pipe. By turning the first coil off or on, the NMR or EMR signal observed at the second coil can be made to change abruptly as the "tagged" element flows to the second coil. By measuring the time of travel of the element of interest evidenced by the second coil signal, the flow velocity can be measured.

Abstract: This method and apparatus is directed to measuring flow velocity of a flowing solid or fluid in a pipe. In the preferred and illustrated embodiment, a single magnet is utilized to impress a magnetic field on the flow, the field having a gradient. A concentrically arranged detection coil is positioned in the field and is connected with a nuclear magnetic resonance (NMR) or electron magnetic resonance (EMR) detection apparatus. A segment of the material moves through the magnetic field. The frequency of a the magnetic resonance signal emitted by the nuclei or electron changes proportionate to field intensity. In a fixed gradient, the time rate of change of the emitted NMR or EMR frequency signal is a linear function of flow velocity. This apparatus provides a measure of flow velocity by interrogating with pulses thereby obtaining a frequency dependent signal.