| 摘要 |
861,927. Magnetic tests. VARIANASSOCIATES. Aug. 13, 1957 [Aug. 14, 1956], No. 25580/57. Class 37. The intensity of a magnetic field is measured by apparatus which produces successive polarizations of gyromagnetic bodies in the field allowing free precession between the polarizations, derives a signal whose frequency is dependent on field intensity, mixes the signal with a fixed signal to derive a further variablefrequency signal and measures the frequency of the third signal. As shown, the gyromagnetic dilutor 1, comprising a coil of wire wound round a sample of water, forms the inductive portion of a tuned circuit, of which the capacitive portion is formed by a bank of capacitors 2 selectively coupled by a switch 3. A programmer 7 which may be merely a switch or a multivibrator operates a polarize-receive relay 4 which first connects a battery 5 to the coil to produce a polarizing magnetic field and then disconnects the battery to allow free precession of the gyromagnetic bodies. The same coil as is used for polarizing the sample is used to detect the precession and applies an output through a narrow band filter 8 tuned in step with the coil 8 by condenser bank 9 and switch 11 to a mixer circuit 12 where it is heterodyned with the output of a load oscillator 13 tunable in coarse steps by condensers 14 and inductances 16 and in fine steps by condensers 18. The lower sideband of the mixed output is selected by a filter 21 and its frequency is either indicated directly on a vibrating reed meter 28 or it is frequency multiplied at 22 and heterodyned with the output of a fixed oscillator 28 at mixer 24, the lower sideband selected at 27 and again frequency indicated on vibrating reed frequency meter 28. A calibration oscillator 32 is provided. In a simplified arrangement (Fig. 3, not shown) the output of the narrow band filter is frequency multiplied and combined with a local oscillator. The lower pass-band is then selected and its frequency indicated directly. In an arrangement for indicating magnetic gradient (Fig. 4, not shown), the arrangement of Fig. 2 is effectively doubled using a common battery, programmer, local oscillator, fixed oscillator and frequency indicator. The two samples are spaced by a known amount and the frequency meter which is of the vibrating reed type gives two readings. A knowledge of the field gradient may be determined by subtracting these readings. |
