Development Of JPM-2 Proton Precession Magnetometer

As a precision instrument to measure the earth magnetic field, Proton magnetometer has many advantages such as easy to carry, simple operation, high reliability and moderate price. It has been widely used in the fields of geological mapping, seismic monitoring, archaeological research, safety inspection and so on. Proton magnetometer works on the phenomenon called Larmor precession. The magnetic field value can be calculated according to the quantitative relationship between the frequency of Lamor precession signal frequency and the geomagnetic field value.Compared with foreign equipment, domestic proton magnetometer performance poor in many aspects. In order to improve various indicators of proton magnetometer especially the sensitivity, analog circuits and digital parts of JPM-2 proton magnetometer are introduced in this paper. In analog circuits, the excitation and reception of Larmor precession signal are studied. The working process of the polarization circuit is introduced, and the design of its switches is explored. To improve the magnetic field measuring range of the instrument, the resonant circuit with adjustable capacitance has been designed. For improving the signal to noise ratio of the system, The circuit including preamplifier and band pass filter has been studied. Then the output square wave of the hysteresis comparator is used for frequency measurement.To realize the function of control, algorithm implementation and data processing, DSP is adopted as the master controller. To ensure the accuracy and stability of frequency measurement, CPLD and TCXO are adopted as the core components of the frequency meter. In this paper, the design of other auxiliary functions are also introduced, such as keyboard, display, external extended memory, data transmission, ADC and so on. As an instrument for field measurements, the human-computer interaction of JPM-2 is introduced.Then some tests, including tests of frequency meter and auto-tune indoor, the sensitivity test of the field have been done. According to the actual experimental data, the initial signal-to-noise ratio of output signal is 17.3, the sensitivity of JPM-2 proton magnetometer by this measurement can reach to 0.15 n T.