A high-precision standard has been established to create a de magnetic field in the expanded geomagnetie range 10 μT to 110 μT. Over this range the systematic standard uncertainty of the total magnetic field is (0.003-0.03) nT, with a random standard deviation of 0.002 nT, inside a sphere 10 cm in diameter. The uncertainty of the magnetic-field direction is 1 second of are. A new type of three-component coil system, with an enlarged working space and an advanced potassium magnetic-field stabilizer, has been designed. The standard is intended for the calibration of high-precision geomagnetometers.
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