| 摘要 |
1,216,861. Measuring fluid-flow. BADGER METER MFG. CO. Feb. 19, 1968 [Feb. 20, 1967; Oct. 9, 1967], No.7937/68. Heading G1N. The invention relates to flowmeters of the type wherein the rate of flow of a fluid containing gyromagnetic nuclei is measured by polarizing the nuclei in a bolus of the fluid at a tagging station 12 and detecting the arrival of the bolus at a nuclear magnetic resonance detection station 14. Each output pulse from the detector may be used to generate a new tagging pulse whereby a metered quantity of fluid is indicated by each pulse and the total flow during any time interval is proportional to the total number of pulses during that interval. In accordance with the invention, there is provided at the detection station a uni-directional magnetic field H 0 and a radio frequency field of constant amplitude H 1 and frequency f transverse to the uni-directional field, and a gradient is established along the flow path in one of these fields to cause a slow adiabatic rotation of the direction of the effective field (the vector sum of H 1 and Ho - 2#f/γ where γ is the gyromagnetic ratio of the polarized nuclei) operating on the polarized nuclei relative to a co-ordinate system rotating about an axis parallel to the uni-directional field with a frequency f. As described with reference to Fig. 1, a gradient is established in the uni-directional field H 0 . Coil 22, coaxial with the flow path, picks up the resonance signal which occurs when the polarized nuclei reach a point in the flow path where Ho = 2#f/γ . In an alternative embodiment, Fig. 7 (not shown), not subject to errors due to fluctuations in r.f. frequency, the uni-directional field H 0 is uniform and a gradient is provided in the r. f. field H 1 . The r. f. coils and pick-up coil may be located centrally of the uni-directional field or at the downstream end thereof. The frequency f of ther. f. field is chosen such that H 0 >> H 0 - 2#f/γ >>H li where H 11 is the amplitude of the r.f. field as the nuclei enter the detection station. A suitable value for f satisfies the relation 2##/H 1 = À02 (where #f is the deviation in cycles per second from the Larmor frequency) for a fluid having a longitudinal relaxation time of about 1 second and flowing at 10ft. /sec. with H 1 equal to À5 gauss at the centre of the pick-up coil. |
