kriswiner
commented
2 years ago Not sure I can help here, the combination of low-pass filter (which is the LPF) and averaging is somewhat redundant. Averaging is, of course, simple running averaging of the data in a buffer before reporting. The low pass filter removes high-frequency noise, so is not an averaging process per se but a filter. They both together result in a lower noise signal, one by removing higher frequency noise and one by removing "all-frequency" noise.
In the end what matters most is the application requirements. Both the LPS22HB and LPS22QS can discriminate height changes of ~10 cm or more with little trouble. The specs of the QS look about 2x better in terms of lower noise, and in fact I find the altitude estimate based on QS pressure data with reasonable noise filtering 1 Hz, (16x averaging, LPF/9 filter quite stable.
I am interested in ultra-low-power usage of these kinds of sensors so for me running at 200 Hz sample rate with heavy averaging is not an option, although this would be a good way to get an even more "stable" baro output. I find the 1 Hz QS performance with modest noise filtering quite acceptable at a cost of 3 uA or so. I think it is better than the HB at the same power cost but I don't have a good way to quantify this.
If you want to understand the details of the noise filtering and what reasonable expectations might be, I recommend you ask ST at their MEMS sensor forum.
On Sun, Feb 20, 2022 at 4:48 PM hpmax @.***> wrote:
I'm curious how this (and the LPS22DF which seems to have similar performance but lacks the 4 bar mode) performs relative to the LPS22HH. They certainly quote much better performance than the LPS22HH, but there's one thing I noted that seems odd...
The quoted accuracy for the LPS22HH is .65 Pa at ODR/20. Which is a lot of filtering... By contrast, the quoted accuracy for the LPS22DF/ILPS22QS is 0.34 Pa at ODR/9 BUT they specify an AVG=512, and max ODR is 200Hz.
The way I see it, a noise spec is only meaningful as a function of bandwidth. ODR/9 sounds like its more than 2x the bandwidth and almost half the noise, which is awesome... But what does AVG=512 mean? Assuming true gaussian noise, averaging 512 elements would be expected to reduce noise by a factor of 512^,5. It's hard to understand how you could average the last 512 samples and still have a bandwidth of 11% of the output data rate.
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hpmax
I'm curious how this (and the LPS22DF which seems to have similar performance but lacks the 4 bar mode) performs relative to the LPS22HH. They certainly quote much better performance than the LPS22HH, but there's one thing I noted that seems odd...
The quoted accuracy for the LPS22HH is .65 Pa at ODR/20. Which is a lot of filtering... By contrast, the quoted accuracy for the LPS22DF/ILPS22QS is 0.34 Pa at ODR/9 BUT they specify an AVG=512, and max ODR is 200Hz.
The way I see it, a noise spec is only meaningful as a function of bandwidth. ODR/9 sounds like its more than 2x the bandwidth and almost half the noise, which is awesome... But what does AVG=512 mean? Assuming true gaussian noise, averaging 512 elements would be expected to reduce noise by a factor of 512^,5. It's hard to understand how you could average the last 512 samples and still have a bandwidth of 11% of the output data rate.