[Ian, Sander]
We attempted to measure seismic noise in various locations using the Wilcoxon accelerometer. We used an AlphaLab LNA10 (see photo) to amplify the signal from the accelerometer, and acquired the data downstream of the amplifer with the Moku:Go.
The problem we found is that the amplifier seems to introduce noise in the measurement that obfuscates the signal from the accelerometer. This can be seen by comparing spectra obtained with the accelerometer connected through the amplifier vs. having just the amplifier connected (i.e. having nothing connected to the amplifier input). The measured spectra in the two cases are almost indistinguishable at amplifier gains of 10 and 100.
The attached spectra are for measurements with gain=1000, where the red traces (input 1) are the measurements of the channel with the amplifier, and the blue trace (input 2) is a reference measurement of an unconnected Moku input. The faded red trace is with the accelerometer connected through the amplifier, the bright red trace is with just the amplifier. The accelerometer was oriented vertically (z-direction).
Further indication that the LNA10 introduces signifcant noise is found by comparing the spectra here to those in entry 11284, which have very different frequency dependences. Those spectra were taken without an amplifier (I think?).
The spectra in entry 11284, was taken with the LNA10. We were certainly seeing more noise than we were on Friday but what I found to be so strange was that there we could not get consistent measurements. For example in the swing space we found that when the Moku Go was being run off my laptops power there was a massive 60Hz line but when we plugged the Moku in the line was gone. And it was not consistent. if we unplugged the Wilcoxon 731A then plugged it back in we would get a different reading. If we power cycled the Moku we would get a different reading. Nothing was consistent. I would think that this might be a bad electrical connection but we checked them all and they seem to be fine. It might be worth it to get a 2-pin MIL-C-5015 connector, which is what the Wilcoxon uses just to be sure but I'm not sure why we are getting such inconsistent measurements.