RESEARCH ON LOW NOISE AND LOW DRIFT FLUXGATE MAGNETOMETER
Hu 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.
Offset
10
5
5
0
0
Z/nT
Z/nT
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.
10
-5
-5
-10
-10
-15
-15
-20
-20
0
10800
21600
32400
43200
54000
64800
75600
0
86400
10800
21600
32400
64800
75600
86400
54000
64800
75600
86400
54000
64800
75600
86400
50
40
40
Sensor
LC
I-V
Phase
shifter
Filter
Integrator
PSD
LPF
Output
30
30
D/nT
20
D/nT
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.
54000
FGE 2009-04-24
Jingxia 2009-04-24
Feedback
43200
20
10
f0
actuator
amplifier
f0
divide
2f0
divide
oscillator
10
0
0
-10
-10
0
10800
21600
32400
43200
54000
64800
75600
0
86400
10800
21600
32400
FGE 2009-04-24
0
-10
-10
-20
-20
-30
-30
-40
H/nT
H/nT
Jingxia 2009-04-24
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.
-40
-50
-50
-60
-60
-70
-70
-80
0
10800
21600
32400
43200
54000
64800
75600
86400
0
10800
21600
32400
6
8
4
6
2
4
0
2
-2
0
-4
-2
-6
-4
-8
-6
0
10800
21600
32400
43200
54000
64800
75600
86400
0
10800
21600
32400
Jingxia 2009-04-23
25
25
20
20
15
15
10
10
D/nT
D/nT
43200
54000
64800
75600
86400
54000
64800
75600
86400
54000
64800
75600
86400
FGE 2009-04-23
5
5
0
0
-5
-5
-10
-10
-15
-15
0
10800
21600
32400
43200
54000
64800
75600
0
86400
10800
21600
32400
-10
-10
-20
-20
-30
H/nT
0
-30
-40
-40
-50
-50
-60
-60
0
10800
21600
32400
43200
54000
43200
FGE 2009-04-23
Jingxia 2009-0423
H/nT
43200
FGE 2009-04-24
Z/nT
Z/nT
Jingxia 2009-04-24
Full-wave rectification have a double fold
efficiency than half-wave rectification,and it
would be improve the device’s SNR.
43200
64800
75600
86400
-70
0
10800
Jingxia 2009-04-23
21600
32400
43200
FGE 2009-04-23
Observation result
24-bits AD VS 16-bits AD
References
Vi
Magnetic
field
DAC
+
sensor
ADC
register
The stability of the background field
biasing circuit affect greatly on the
device output’s drift and noise.
[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.
MCU controller
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