GB810596A - Gyromagnetic resonance method and apparatus - Google Patents

Abstract

810,596. Gyromagnetic resonance apparatus. VARIAN ASSOCIATES. June 15, 1955, No. 17310/55. Class 37. [Also in Groups XVIII and XL (b)] Gyromagnetic resonance apparatus for analysis of materials comprises the known arrangement of a permanent magnet &c. for subjecting the materials to a unidirectional field, a coil for subjecting the materials to a radio-frequency field at right angles to the unidirectional field and a pick-up coil (not shown) having its maximum response to a field perpendicular to the two other fields together with means for integrating the signals due to gyro-magnetic resonance picked up by this coil. The integrated signal may be measured directly or indirectly. The system may be applied to the analysis of a water-oil mixture and to the determination of the moisture-content of flowing grain &c. Integrating and measuring circuit (Fig. 3). Meter 25 responsive to the potential difference between the anodes of triode valves 23, 24 is initially set to zero by means of potentiometer 27. The pulses due to gyro-magnetic resonance after amplification at 14 and integration in circuit 19, 21 upset the balanced condition of the valves 23, 24. Balance is restored by a further adjustment of 27, the new setting of which indicates the E.M.F. due to the precessing nuclei. Measuring moisture content (Figs. 3, 4, 5 and 7). In Fig. 4 measurement of gyromagnetic resonance is performed on flour in a diamagnetic (e.g. glass) hopper 32. In Fig. 5 galvanometer 25 (Fig. 3) is set to zero by resistor 27 while gyromagnetic resonance signals are being received from a standard sample 44. A suitable volume of test substance is then placed on top of sample 44 which moves against spring 46 and allows the test substance to come into the measuring position. Any further adjustment of potentiometer 27 needed to zeroize galvanometer 25 indicates the deviation of moisture content from the standard. In Fig. 7 the measurement is corrected for changes in density of the fluent material measured by a gamma-ray detector 58. Signals from the detector modify the bias and hence the gain of valve 66 in the path of the gyromagnetic resonance signals. Compensating for leakage signals in pick-up coil (Figs. 8 and 9 and Figs. 10, 11 (not shown). Triangular waves from sweep generator 85 vary the polarizing field and square waves from generator 84 are synchronized with the triangular waves as shown in Fig. 9 so that resonance points Ho occur when the square waves are at high level. The square wave output of generator 84 is transmitted to a relay 92 with two pairs of make and break contacts. The D.C. signal from cathode follower 88 is applied to integrator 89/91 and during high level of the square wave is a composite signal which consists of a component due to leakage flux from transmitter coil to pick-up coil and a component due to precessing nuclei in the substance under test. During low level of the square wave the signal from cathode follower 88 consists only of the leakage voltage. Throughout high level of the square wave, condenser 91 is in one connected direction and during low level, relay 92 changes over to reverse condenser 91. Thus the leakage voltage is subtracted from the composite signal so that the integrated signal is only that due to the precessing nuclei. The output from this flip-flop integrator may be connected to the null balancing circuit as shown in Fig. 3. The square wave and triangular wave frequencies may be the same so that two resonance points occur during each high level of the square wave, Fig. 10 (not shown). According to Fig. 11 (not shown) two integrator circuits are associated with the cathode follower 88 alternately and act differentially on the records so as to produce a nett output due only to the precessing nuclei. Specification 810,597 is referred to.