Measurement and analysis of earth's magnetic field based on low-magnetic field standards
The Cheongyang (CYG) observatory has been built to measure earth's magnetic field and to study prediction of earthquake and space weather. The equipments of the CYG observatory are a 3-axis fluxgate magnetometer, an overhauser effect proton magnetometer, a declination/inclination magnetometer and a data logger. A Cs-4He atomic magnetic resonance magnetometer was used to correct the measured data obtained by the proton magnetometer. All the measurement equipments were calibrated using magnetic field standard system maintained at KRISS. The Measurement results show a variation of the baselines less than 5 nT within one year, which is the most critical requirement criteria for joining the INTERMAGNET (International Real-time Magnetic Observatory Network).
Maintenance of magnetic flux density standards on the basis of proton gyromagnetic ratio at KRISS
The proton gyromagnetic ratio (/spl gamma/'/sub p/) plays a fundamental role in achieving high accuracy in magnetic measurements. We have improved our magnetic flux density standards using the /spl gamma/'/sub p/-value and related techniques developed at Korea Research Institute of Standards and Science (KRISS). The standards are used for the calibration of magnetometers and support the test of sensors and materials in the range from 20 /spl mu/T to 2.5 T with (4 to 80) /spl mu/T/T uncertainties (k=2).
Atomic magnetic resonance based current source
A current of 1 A has been stabilized by locking the magnetic resonance frequency of Cs atoms placed at the center of a solenoid. Two auxiliary windings are used to obtain at the center of the solenoid a field uniformity better than 0.5 ppm in a 2 cm radius sphere, in agreement with the calculations. The variations of the external field and the effect of temperature changes are compensated for by two auxiliary feedback systems using a flux gate magnetometer and an adjustment of the locking frequency, respectively. The current fluctuation, including the noise of the current measuring system is 0.1 ppm and the current drift for 6 h is less than 0.2 ppm.