Design And Implementation Of Proton Precession Magnetometer Based On DSP

The proton magnetometer is a static magnetic field measuring device base onthe phenomenon of proton precession. The instrument has already been used widelyin magnetic observatories, geotechnical or archaeological exploration, marinemagnetic prospecting, etc. The principle of traditional proton magnetometer issimple, a large current is passed through the solenoid coil to generate a largemagnetic field in the core in order to line up the protons, and all of protons arepolarized in a given direction. Then the polarizing field will be turned off, theprotons will precess around the ambient magnetic field and induce the larmor signalin the solenoid coil, the signal whose frequency is proportional to the magnitude ofthe field.In order to improve the comprehensive performance of proton magnetometer,JPM-1proton magnetometer is introduced in the paper, which is based on digitalsignal processor (DSP) TMS320F2812and different from previous domesticmagnetometer. The DSP as the core is used to achieve the acquisition and processingof proton precession signal, and the frequency counting method based onzero-crossing counting algorithm is employed in our magnetometer. This paperintroduces the basic principles of proton magnetometer at first, and then gives thewhole system design and the key technologies to improve measurement accuracy ofproton magnetometer. The signal-to-noise ratio of proton precession signal isconsidered in paper, which is discussed based on signal strength and instrumentnoise. The signal to noise ratio of JPM-1type proton magnetometer depend onmeasured data is given. In measuring the frequency, the relative error due to signalto noise ratio of proton precession signal, is considered exactly too. So the instrument needs to have as high signal to noise ratio as possible. The partialfunction realization of the system is explained in details, including signal detectioncircuit and digital modules circuit. The power supply module, controller module,display module, clock module and other functional module, was designed for JPM-1proton magnetometer. Then frequency measurement algorithms which processtime-series of signal’s zero crossing is presented. The basic functions of JPM-1proton magnetometer ware showed, and the system of the entire software design wasintroduced. Finally, the results of the instrument measurement ware presented,including the instrument sensitivity and the contrastive results with the GSM-19T.Final results show that the initial signal strength is about0.4μV with signal to noiseratio32:1, and0.27nT sensitivity is obtained in field measurement.