A frequency measurement method using rising-falling edge of square wave for increasing proton magnetometer precision

To improve the measurement precision of the proton magnetometer (PM), a multi-average multi-cycle frequency measurement (M-MFM) method using both rising and falling edge of square wave is proposed in this study. First, the M-MFM method using Rising-Falling edge of square wave is presented based on the multi-cycle frequency measurement (MFM) method, and the formula of frequency measurement is deduced. Then, the relative error of the proposed method is analyzed, and the proposed method is optimized by solving the minimum value of the relative error formula. Finally, the implementation process of the proposed method in STM32 is introduced. The experimental results of the frequency measurement demonstrate that the measurement precision for low SNR sine signals is significantly increased by the proposed method. The experimental results of the magnetic field measurement show that the sensitivity is about 0.11 nT/Hz
^1/2
@0.25 Hz in the range of the geomagnetic field while the proposed method is adopted by the PM, which is better than that of the other methods and the commercial instruments.