Po Gyu Park

Magnetic flux density standard for geomagnetometers

A high-precision standard has been established to create a dc magnetic field in the expanded geomagnetic 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 arc. 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.

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.

Precise standard system for low dc magnetic field reproduction

A standard system for low magnetic fields has been developed at the Korea Research Institute of Standards and Science. The system consists of a precision solenoid, He–Cs atomic magnetic resonance magnetometer, and apparatus for three-axis compensation of the Earth’s magnetic field. The variations of the Earth’s magnetic field are automatically compensated within 0.1 nT/h by a Cs atomic magnetic resonance field controller. The solenoid reproduces a dc field that is uniform at better than 3×10−7 within ±2 cm around the center. The experimentally measured coil constant and temperature coefficient of the solenoid are 1.231 0596×10−3 T/A (25 °C) and 3.8×10−7/°C, respectively. The standard serves for the calibration of magnetometers and uniform field coils, and also supports experiments related to research in magnetic fields in the range of (0.02–1.2) mT with (2–10)×10−6 uncertainty.

A high-precision system for direct current reproduction based on atomic magnetic resonance in helium-4

At the D. I. Mendeleyev Institute for Metrology (VNIIM) a high-precision system using helium-4 atomic magnetic resonance has been realized for the automatic reproduction and maintenance of direct current in the range 0.1 A to 1.0 A. A random standard uncertainty of 2 × 10-8 was obtained for stabilization at 1 A, with a non-linearity of less than 2 × 10-7 in the frequency-to-current conversion factor. The conversion factor was determined experimentally through the gyromagnetic ratio of helium-4 atoms and the calculable coil constant of a high-precision solenoid. The technique was used to determine the gyromagnetic ratio of the proton and for the accurate reproduction of the tesla using the calculable solenoid.

Low-field method for measuring proton gyromagnetic ratio

A measurement of the proton gyromagnetic ratio in water by the low-field method is in progress. The Earths magnetic field is compensated down to 1 nT at the center of Helmholtz coils in the constructed nonmagnetic facilities. The solenoid former of fused silica has been fabricated by the screw grinding and lapping within the dimensional variations of a few micrometers. >

AC magnetic flux density standards in the low frequency range

An AC magnetic flux density standard system was constructed for calibration in KRISS magnetometers and for the testing of the magnetic field characteristics of sensors and materials in the frequency range below 20 kHz. This system consists of an AC magnetic field converter, a Helmholtz coil, a voltage comparator, a voltmeter, a standard resistor, and a computer with a program for automatic measurement. The expanded uncertainty (k=2) is 0.2% in the range of 1 Hz to 20 kHz.

International comparisons to establish the traceability in the global network of geomagnetic observatories to SI units

The international comparisons in the field of earth-level dc magnetic flux density measurements with the participation of six National Metrology Institutes (NMIs) and four geomagnetic observatories (GMOs) have been carried out in 2013 and 2014 under the auspices of the Regional Metrology Organization Asia Pacific Metrology Programme (APMP). The obtained expanded uncertainty (k = 2) of the weighted mean value of correction values does not exceed 0.1 nT in the range of 20 μT to 100 μT, which was one of the main aims of this comparison. VNIIM (D I Mendeleyev Institute for Metrology) was the pilot laboratory for this comparison registered in the Key Comparison Data Base (KCDB) under index APMP.EM-S14. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Ac/dc magnetic flux density standard systems at KRISS

The ac/dc magnetic-flux-density (MFD) standard systems were developed for the calibration of magnetometers and the test of sensors and materials. The dc MFD is maintained to cover the range from 20 µT to 2.5 T with the expanded uncertainties (k = 2) from 4 µT/T to 80 µT/T. The expanded uncertainty (k = 2) of ac MFD standard is 0.2 % in the range of 1 Hz to 20 kHz. We had been participated in international key comparison to achieve the equality and the mutual agreement between standard institutes for the results of calibrations and tests.

Standard measuring system for calibration of magnetic flux density gradiometers

A standard measuring system (setup) has been developed at VNIIM to be used for the calibration of magnetic flux density gradient (MFDG) coils, sensors and magnetic gradiometers (MG). This measurement standard is based on the calculable quartz coil used for the reproduction of gradient which is uniform in a specified working space. It also includes measuring equipment to compare coils, gradiometers and differential measuring transducers. Theoretical and experimental aspects of the problem are discussed. The developed standard system allows calibrating MFDG coils with an uncertainty of 0.1 % within the range from 0.005 to 0.5 T/m.

Power calibration system based on Josephson sampling voltmeter

This paper describes system setup, based on a Josephson sampling voltmeter for precision power calibration. The waveforms generated by voltage and current sources, which are applied to a power meter under test, are transformed to 1-V level voltage signals and measured by a single Josephson voltmeter with a uncertainty (k = 2) less than 0.5 μV/V.