I am using an ADXL375 in one of my projects. What I am observing is that the bias changes significantly with the output rate. So, the calibration performed at a lower data rate doesn't work for a higher data rate. Is this suppose to happen?
Thanks for your question. When you said "bias", do you mean both the sensitivity and offset change based on ODR? If so, it's not something expected to happen. By the way, how do you calibrate the part? Do you use this 200g part to measure impact events? I think the offset calibration for the part is not necessary for such application because you'll be more interested in the AC signal.
Hope this helps.
By bias, I meant the offset. I am sampling at 2 rates:
1) 25 samples/second with 25 Hz ODR and filter set at 12 Hz.
2)1000 samples/second with 800 Hz ODR and filter set at 400 Hz.
I calibrate the sensor using the gravity based multi-position method.
Yes, I intend to measure 40-80 g impacts using this sensor, but some applications require low g data too.
The magnitude of acceleration at 25 Hz is 1.3752, while it is 0.8866 at at 1000 Hz, when the sensor is at rest. It is significantly different. Since, the sensor is at rest, it should ideally be 1 and not different at different rates.
Why is this happening?
I did a rough calculation based on the 49mg/LSB sensitivity and it turns out to be ~10LSB shift which seems a little large. Let me try to check if I can find such test results in our characterization report for this particular part.
Unfortunately, I didn't find any related test results for the particular part under such condition. Having said that, all the error sources should be counted within the min/max spec for the 0g offset, which is +/-6g for the ADXL375.
The offset is under +/- 6 g, which is fine as long as I can calibrate it. The problem is that it is changing by changing the update rate (Frequency). I have never experienced this with other sensors before. The sampling rate shouldn't effect the offset.
Yes, I understand your concern here. Unfortunately, if you do want to switch ODRs in your application, you may want to calibrate under different scenarios. Otherwise, you can just stick with one ODR.
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