Improvements to the NMR Method With Flowing Water at CMI

Nuclear magnetic resonance (NMR) is a very important technique for making accurate measurements of the magnetic flux density B of dc magnetic fields in a wide range of values. This paper presents improvements to the NMR method with flowing water (the nutation method). The method is used at the Czech Metrology Institute and provides an improved signal-to-noise ratio of the amplitude of the NMR signal, new resonance frequency value by searching nutation double pattern recording, and an improved calibration uncertainty value. This method is used for calibration of the coil standards of magnetic flux density with a constant value below 20 mT/A. Using the improved nutation method presented here, the magnetic flux density coil standard can be calibrated within a period of less than 30 min in the range of 0.1 to 100 mT with expanded uncertainty of 20 to 60 ppm.