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Precision magnetometer
Diagram of the Earth’s magnetic field from www.philips.com .
Applications of high sensitivity magnetometers:
A magnetometer is used to measure the strength of the Earth’s magnetic field. To get a feel for the sensitivity of these magnetometers, the earth’s magnetic field strength in London on 24 SEP 2005 was 48,489 nT, increasing by 31.43 nT per annum. The 0.100 nT accuracy of the potassium magnetometer is very close to the 0.086 nT daily increase in the earth’s magnetic field strength, in London.
- geophysical surveys measuring the minute variations in the Earth’s magnetic field strength, to identify the location of mineral Kimberlite pipes and provide hints as to the location of hydrocarbon deposits
- compliment seismic surveys, in oil and gas exploration work
- detect underground metallic structures, such as pipes, tunnels, barrels, items of archaeological importance
- detect the presence of metallic structures in dense foliage, such as trucks, pipes, crashed aircraft, artefacts from lost civilisations, using differential magnetometry
- detect metallic structures under rivers and oceans, such as pipes, ship wrecks
- detect the presence of intruders in dense undergrowth, such as armed militia, with metal guns, possibly travelling on metal bicycles, motorbikes, or, in metal trucks…
The Earth's total magnetic field intensity in nT.
from http://www.gemsys.ca/PDFDocs/MM3_GEM_Brief_Review_of_Quantum_Magnetometers.pdf
from JamesMacnae presentation at SEG 2006
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Typical Detection Range For Common Objects |
||
|
Ship 1000 tons |
0.5 to 1 nT |
at 244 m |
|
Light Aircraft |
0.5 to 2 nT |
at 12 m |
|
Pipeline (12 inch) |
1 to 2 nT |
at 60 m |
|
Pipeline (6 inch) |
1 to 2 nT |
at 30 m |
|
Automobile |
1 to 2 nT |
at 30 m |
|
100 Kg of iron |
1 to 2 nT |
at 15 m |
|
45 Kg of iron |
0.5 to 1 nT |
at 9 m |
|
4.5 Kg of iron |
0.5 to 1 nT |
at 6 m |
|
0.45 Kg of iron |
0.5 to 1 nT |
at 3 m |
|
Screwdriver 125 mm |
0.5 to 2 nT |
at 4 m |
- from http://www.heritagegeophysics.com/Magnetometers/Magnetometers.htm
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sensor |
type |
accuracy in pT |
noise level in pT/sqrt(Hz) |
|
solid state magnetoresistance eg. Honeywell HMC1001 / HMC1002 |
TENSOR |
50,000 |
850 |
|
Fluxgate magnetometer eg. Bartington Mag-03 |
TENSOR |
350 |
< 6 |
|
Potassium beam magnetometer eg. Gem Systems GSM-19 |
SCALAR |
100 |
< 15 |
|
low temperature (liquid Helium) SQUID eg. Supracon |
TENSOR |
only noise limited |
< 0.5 |
For reference, the Earth’s magnetic field strength at London on the 24th September 2005 was 48,489,000 pT.
Magnetic field strength is often quoted in Gauss. 1 Tesla = 10,000 Gauss.
- from Honeywell application Note An211.pdf as found on www.magneticsensors.com site.
These compact, high performance fluxgate sensors with integral electronics provide precision measurements of static and alternating magnetic fields in three axes. They are available with measuring ranges of ±70, ±100, ±250, ±500 or ±1000μ T in a range of enclosures as detailed below. Powered from any ±12V supply, outputs are in the form of three analog voltages from 0 to ±10V, proportional to Bx, By and Bz.
Low noise sensors with a noise level of < 6pTrms/√ Hz at 1Hz can be supplied in all enclosures (except MCT) with a measuring range of ±70 or ±100μ T
|
Performance specification |
|
|
Supply voltage |
±12V to ±17V |
|
Analog output |
±10V (±12V supply) swings to within 0.5 of supply voltage |
|
Power supply rejection ratio |
5μ V/V |
|
Output impedance |
10 ohms |
|
Linearity error |
< 0.0015% |
|
Frequency response |
0 to 1kHz maximally flat, ±5% maximum above 1kHz |
|
Calibration error |
±0.5% |
|
Bandwidth |
0 to 3kHz (5kHz for Mag-03IEV 1& 2 on request) |
|
Orthogonality error |
|
|
between sensing axes |
< 0.5° (< 0.1° for Mag-03MS and Mag-03MSES) |
|
Z axis to reference face |
< 0.1° (Mag-03MS and Mag-03MSES only) |
|
Single sensor axis to body |
< 3.5° (Mag-03IE sensors only) |
|
Internal noise |
|
|
standard version |
< 12pTrms/sqrt(Hz) at 1Hz |
|
low noise version |
< 6pTrms/sqrt(Hz) at 1Hz |
|
Supply current |
|
|
standard version |
+35mA, -6mA (+1.4mA per 100μ T for each axis) |
|
low noise version |
+26mA, -6mA (+1.4mA per 100μ T for each axis) |
Typical noise spectrum for low noise version (0.1 to 10Hz)
- from http://www.bartington.com/media/598b5f59/DS0013MAG03.pdf
- from Electronics Weekly, 9th January 2005
|
The SQUID = Super Conducting Quantum Interference Device magnetic field sensor |
from “LTS SQUIDS: …” by A. Chwala et al, www.supracon.com
|
Comparative sensor noise during winter atmospheric (“sferic”) disturbance |
From James Macnae presentation at SEG 2006
© Barnard Microsystems Limited 2006 - 2008