The hall effect sensor is quite noisy, and I am trying to find where the noise comes from. The first I tried today is to measure the **power spectrum and coherence among three hall effect sensors (in the vertical direction)**. Here is the result:
(the unit for the power spectrum density is in digital volt per root hertz.)
I do not quite understand **why ****there is almost no coherence (apart from the 60Hz power line), even though the power spectra are almost identica**l among these sensors.
Can someone shed some light where the issue is? **Is the noise non-stationary or what? **
--------**Another measurement with fewer average**---------------------
It seems that when the number of average is small, the coherence is large, an indication of non-stationary? |