Magnetic resonance magnetometer is a precision measuring instrument based on the strict linear correlation between the frequency of nuclear resonance and the strength of magnetic field. However

due to the limitation of bad SNR in weak field

its measurement range is generally not less than 20 mT. In order to expand its ability to measure weak magnetic field

a new method using flowing water based on the pre-polarization technology was studied. By constructing the mathematical physics equation of the measuring process

the optimization method of the measurement curve was given. By pre-polarization treatment

the intensity of the magnetic resonance signal increased by 4.54 times. By using the CPMG sequence in signal detection

the hardware demand reduced and the stability of the measurement could be enhanced. By data fitting

the measurement spe

ed and precision were improved. Finally

the width range of 0.078 8～1.373 mT magnetic field was measured in a homemade 48 mT nuclear magnetic resonance device with low uniformity(about2×10

-4

)

and the measurement accuracy was less than 0.1 μT.