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I'm verifying the Bosch SMI230 accelerometer, and the documentation states that the zero-g offset temperature drift is ±0.2 mg/K. I want to calculate the upper and lower limit values for the 0 g offset. For example, at -20°C, the upper limit is -20 * 0.002 g? And at 80°C, the upper limit is 80 * 0.002 g?

Figure 1 shows my test data, where I tested the zero-g offset of the sensor in a temperature chamber from -20°C to 85°C.

Another question is whether I should verify the upper and lower limits of the 0 g offset versus temperature, or if I only need to ensure that the acceleration values do not exceed the zero-g offset (including temperature) of 20 mg between -20°C and 85°C?

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From the datasheet, this is the relevant specification:

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The upper and lower limits are stated to be +/-20mg.

The temperature drift specification is only valid over the "full temperature range", which is -40C to +105C. The usual interpretation of such a spec is that if draw a box that encloses the highest and lowest offset (Y-axis) and has a width of the full temperature range that all offsets observed will be within that box. It might fluctuate up and down within that box (which you are indeed observing)- there is no guarantee that it is monotonic nor that the slope of mg offset per degree will not exceed +/0.2.

So if it never exceeds +/-20mg and the height of the 'box' is smaller than 29mg it is within specifications.

Of course you'll have to use a test procedure that eliminates the effect of gravity. I believe there is a relevant standard.

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  • \$\begingroup\$ 29mg? Isn’t it +/-20mg? \$\endgroup\$ Commented Oct 16, 2024 at 1:33
  • \$\begingroup\$ 145 degrees multiplied by the +/-0.2 \$\endgroup\$ Commented Oct 16, 2024 at 5:37

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