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modified LIS2DW info

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Félix Boisselier
2024-01-09 09:02:49 +00:00
parent d71e385ad9
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docs/macros/axis_tuning.md
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@@ -139,11 +139,11 @@ The presence of an unbalanced or badly running fan can be directly observed in t
### Noisy accelerometer ### Noisy accelerometer
The integration of LIS2DW as a resonance measuring device in Klipper is starting to be more and more common, particularly due to some manufacturers promoting its superiority over the established ADXL345. However, a critical analysis of their respective datasheets reveals a nuanced reality. While the LIS2DW offers a higher sampling rate, which is a marginal benefit for our purposes, it tends to be less sensitive or exhibits increased noise levels at comparable sensitivity settings compared to the ADXL345. But, given that LIS2DW chips are also 5-10 times cheaper, it definitely makes sense for mass-producing PCBs. The integration of LIS2DW as a resonance measuring device in Klipper is starting to be more and more common, particularly due to some manufacturers promoting its superiority over the established ADXL345. A critical analysis of their respective datasheets reveals a nuanced reality: the LIS2DW offers a higher sampling rate, but also it tends to exhibit increased noise levels at comparable sensitivity settings compared to the ADXL345. But, given that LIS2DW chips are also 5-10 times cheaper, it definitely makes sense for mass-producing PCBs.
In our use case, this elevated noise manifests mainly in the spectrogram as additional 'ghosting' resonance lines parallel to the main resonance diagonal, with some intersecting interference lines that skew across the harmonics. Fortunately, this apparent 'lightshow' do not distort the overall shape of the top graph and both the resonant frequency and damping ratio remain accurately measured as well as the input shaping filters that are also quite similar. This only makes it more challenging to discern fine details that could be masked, and it doesn't help for diagnosing mechanical issues. In our use case, this chip manifests aliasing in the spectrogram that can be seen as additional 'ghosting' resonance lines parallel to the main resonance diagonal, with some intersecting interference lines that skew across the harmonics. Fortunately, this apparent lightshow do not distort the overall shape of the top graph and both the resonant frequency and damping ratio remain accurately measured as well as the input shaping filters that are also quite similar. This only makes it more challenging to discern fine details that could be masked, and it doesn't help for diagnosing mechanical issues.
Finally, please note that LIS2DW are known to add a small offset all over the top graph. So the curve and peaks might be a bit higher, even at very low frequencies: in this case, this is probably not [#low-frequency-energy] but just some noise. Finally, please note that LIS2DW are known to add a small offset all over the top graph due to this aliasing. So the curve and peaks might be a bit higher, even at very low frequencies: in this case, this is probably not [#low-frequency-energy] but just some noise and it's not a mechanical problem.
| LIS2DW measurement | ADXL345 measurement | | LIS2DW measurement | ADXL345 measurement |
| --- | --- | | --- | --- |