Instrumentation & Measurement Magazine 23-5 - 48
Fig. 9. The RMSD vs. SNR comparative experiment. (a) Comparison between the MPM method and the M-MFM method when both edges are used; (b)
Comparisons between the three cases of the M-MFM method: using both edges, using only the rising edge, and using only the falling edge.
SNR is lower than 30 dB, the RMSD of the proposed method
is better than the same method adopting only rising or falling
edge, however, it is almost the same when the SNR is larger
than 30 dB.
Magnetic Field Measurement Experiment
produced by the same method using only rising or falling
edge. Moreover, the fluctuation value of the magnetic field
obtained by all of the approaches are smaller than 1nT in a
short time.
The sensitivity is a very important parameter in the magnetometer or the magnetic sensor [23], which represents the
discreteness of measurement. If the sensitivity of the PM is
small enough, the precision will be high enough on the condition that the standard frequency is good enough. Sensitivity
can be estimated by the RMSD in the time domain and also
can be calculated by the noise power spectral density (NPSD)
in the frequency domain [24]. The values of the RMSD in Fig.
10a are 0.20 nT, 0.31 nT and 0.33 nT, respectively. These results are larger than that described above because of the noise
The magnetic field measurement experiments in standard
equipment were performed to verify the effectiveness of the
proposed method for the PM. The experimental setup was displayed in Fig. 5d, where the PM sensor was set to the center
position of the three-dimensional double standard magnetic
field generation coils, and the PM prototype and the PC were
located far away from the coils to reduce the electromagnetic
interference. Meanwhile, the sampling interval time of the
prototype was set to two
seconds (the sample rate
is 0.5 Hz). One second was
used to excite the sensor,
and the rest of the time was
used to measure frequency,
calculate measured magnetic field, and transmit
data to PC by serial port.
Eight magnetic field points
were selected for the comparison experiments: from
20 μT to 100 μT, which is the
range of global geomagnetic field. They are 21 μT,
30 μT, 38 μT, 53 μT, 60 μT,
69 μT, 81 μT , 93 μT and
100 μT.
Fig. 10a is the measurement curve for the case
of 53 μT, which indicates
that the curve produced
by the proposed method
Fig. 10. The curves of comparison experimental results between different approaches at 53 μT. (a) 300 samples, one
sample per two seconds; (b) NPSD results of three methods.
is smoother than that
48
IEEE Instrumentation & Measurement Magazine
August 2020
Instrumentation & Measurement Magazine 23-5
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