RESEARCH ON LOW NOISE AND LOW DRIFT FLUXGATE MAGNETOMETERHu Xingxing, Teng Yuntian, Xie Fan,Zhang Yang

Institute of Geophysics,China Earthquake Administration

There’s no limit on the improvment of the fluxgate magnetometer’s sensitivity,it only depend on the development of the technology.The noise and drift of a magnetometer mainly derive from the following facts:1.The temperature vary affect on the lower frequency signal.The deformation of sensor coil with temperature change the flux in it,that will be make noise.Futhermore,the temperature vary or it’s self gravity would deform the coil bracket too,and it make coil’s output drift while under the background magnetic field which is about 60000nTs.2.Unstability of biasing circuit would greatly add the output signal’s drift of the device.3.The integrator which is the last stage of the analog signal processing circuit of the sensor is used to smoothing filter and enhance the gain of the circuit,yet it would be an great noise and drift source while there is imperfect parameter of operational amplifier.4.Because the driver stage’s output is powerful,the higher order harmonic wave of non-sinewave would enter the signal prcessing circuit and to be noise.5.If the analog signal processing circuit’s bandwidth is too higher,or the efficiency of the phase demodulation circuit is lower,the system’s noise would be added.6.The data-acquisition circuit’s self-resolution or dynamic range is the last guarantee of the device system.

References

[1] ZHANG X F,LU Y L. Technology of Magnetometer[M]. Beijing:National defence industry Press. 1995,123-151.[2] LIU J,DUAN H M,LI W.The Technology Study for Magnetic Detection of Flux-Gate Magnetometer in Well. Equipment for Geotechnical Engineering[J].2007,8(5):21-23.[3] Hu X X,TENG Y T,XIE F,HE R,HUANG J G.Design of Flux-gate Megnetometer’s Auto-compensation[J]. Chinese Journal of Scientific Instrument,2010,31(4):956-960.

IAGA WORKSHOP 2010, CHINA

One of the mainly affect on the sensor’s noise level is the vary of temperature,because it would cause the deformation of the sensor and the mounting rack.And the deformation will make the output drifting when the sensor is put in the magnetic field which is about 6,000nTs.Therefore,the material of the sensor and its mounting blacket must be good temperature stability.

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The other important noise source is all kinds of odd harmonic of the actuator voltage.Make use of sine wave for actuator and set higher order filter would reduce greatly the noise.

Because of the input offset voltage Uio,the input offset current Iio,1/f noise ,and its temperature drift etc,the integrator itself would make great low frequence noise.Decrease the magnification of the integrator would reduce effectively the system noise.

Full-wave rectification have a double fold efficiency than half-wave rectification,and it would be improve the device’s SNR.

24-bits AD VS 16-bits AD

The stability of the background field biasing circuit affect greatly on the device output’s drift and noise.

Observation result

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