Maintenance and dissemination of the magnetic field unit at PTB

The natural line width of low field nuclear magnetic resonance spectra

“…The water quality according to EN ISO 3696 [11] is better than grade 2, showing a conductivity of about 0.3 lS/cm at 25°C. The measurements were performed using an existing NMR free precession measuring system built for the dissemination of the unit Tesla of the DC magnetic flux density [12]. The polarization field of 5.5 mT, generated by a Helmholtz coil with 100 mm inner diameter and a coil constant of 6 mT/A, was applied for 5 s. The detection field was generated by using a Helmholtz coil in combination with a three axial coil system according to Braunbek [13], which compensates the Earth's field down to a value of about 10 nT.…”

Performance of low frequency magnetic field meters to sinusoidal and beat-phenomenon magnetic fields

“…Note that the error of meters 2,4,7,9,18,22,23,31, and 34 at 10 kHz is considerably larger than the average error. Figs.…”

“…Although the standards [12,14] recommend that calibrations should be performed at frequencies far beyond from the resonance frequency of the coil system, they do not propose a specific frequency limit or correction procedure. Nevertheless, there are standard procedures to find the correction function of each coil system [22] that could improve the frequency performance of the meters.…”

“…Weyand [22] presents different methods which are used at the Physikalisch-Technische Bundesanstalt 1 (PTB) to disseminate the unit of magnetic flux density. The author states that field coils, like Helmholtz coils, have proved to be reliable magnetic field generators for industry, if their coil constants are calibrated together with the current measuring instrument, i.e., the coil and the instrument are to be regarded as a combined standard system.…”

AC magnetic field standard for magnetometer calibrations at NMIJ

“…The DC magnetic field can be precisely decided and realized using nuclear magnetic resonance (NMR) system [4][5] and the AC magnetic field can be expanded from this precise DC magnetic field standard [4]. However, it is known that it is difficult to realize the AC magnetic field at the frequency bands more than dozens of kHz when the AC magnetic field is expanded from the DC magnetic field.…”