【摘要】 文中系统地介绍了质子旋进磁力仪的基本原理,检取质子旋进讯号的方法,测量地磁场总强度的方法和精度,磁力仪结构与部件的设计要点,以及仪器观测所得的某些初步结果。更多还原

【Abstract】 This paper introduces systematically the basic principles of the proton precession magnetometer and the method for picking up the proton precession signals. Deduced from the free precession induction, the equationsuggests. 1 ) The induced precession signal is a simple harmonic voltage which attenuates with the exponential law. Its frequency is in proportion to the absolute value of the total intensity of the earth’s magnetic field. Therefore, the measure-ment of the precession signal should be done at the initial of the precession pro- cess so as to obtain higher S/N ratio and to guarantee the precision of the frequency measurement. 2 ) With a view to obtaining stronger induction signal, the coil should have a greater winding number N, the winding should have greater section S, the filling coefficient a of the sensor should be high and the excitation magnetic field H0 should be strong. 3 ) The precession signal induced is the strongest when the axial orientation of the coil is perpendicular to the earth’s magnetic field F, i. e. θ= 1. Nevertheless, the leveling and orienting of the sensor are not strictly required. 4 ) The strength of the proton precession signal is also in proportion to the precession angular frequency ω=γpF. Therefore, higher absolute value of the total intensity of the earth’s magnetic field will produce stronger precession signals.The method for measuring the total intensity of the earth’s magnetic field and the accuracy of such measurement is also delt with in this paper. It seems to the author that among the different methods for the measurement of the total intensity of the earth’s magnetic field through the measurement of the proton precession frequency, the digital frequency meter is better than the beat method and the digital period meter since it allows the direct reading of the observation result in unit of gammas not involving any chart-measurement and conversion. Using the ZX 2 proton magnetometer as a sample, the author has made errorcalculations of the equation F=2π/γp N/nt.The result from the calculation showsthe observation error of the instrument comes chiefly from the error in the determination of the proton gyromagnetic ratio as well as the multiplying error of the frequency multiplier. To raise the observation accuracy of the proton magnetometer, the instrumental scientists have to reduce the multiplying error of the frequency multiplier in addition to raising the precision in the determination of Vp.The following should be observed in designing the structure and the parts of the proton magnetometer. 1) Use of the noise-cancelling sensor which is tuned in by condensers and coupled to the input stage by a step-up transformer. The input stage should have high impedence and low noise. 2) In the phase-locked frequency multimeter, effort must be made to raise the characteristic slope of the phase discriminator and to raise the linearity and characteristic slope of the voltage controlled oscillator by reducing the ripple in the D. C. voltage of the active low-pass filter output. 3) The accuracy and stability of the oscillation frequency of the crystal oscillator should be greater than 1×10-6.It is suggested to use the time controller consisting of the frequency divider and the AND NOT-gate decoder as shown in Fig.5, so as to guarantee the timing accuracy. 4) The discrimination capability of the instrument should better be 0.1 gamma, Finally, some preliminary results of the observation carried out at the geomagnetic stations in Beijing, Wuhan and Guangzhou are presented. Calculation of these results shows the instrument has a mean spuare error≤1 gamma.更多还原