What is the recommended approach to sensitivity calibration of the Z-axis?
In our application we consider that the device holding the sensor may change orientation and we discount gravity from our acceleration measurements to enable us to use an activity threshold of less that 1g, and for this reason we do a modified offset calibration often during the normal operation of the application. Our offset calibration includes discounting gravity.
We are calibrating ADXL343 for acceleration measurements. When stimulating ADXL343 in the direction of the Z-axis together with a reference measurement of the acceleration, we find the sensitivity, i.e. the value that according to the data sheet is typically 256 LSB/g in full resolution, but may vary between individual ADXL343 parts. We store this calibration sensitivity value in our application to present an accurate acceleration measurement. For our calibration experiments we use an acceleration rigg that produces 7-9g.
In the Z-axis we see that the sensitivity is of a certain value in the positive direction and another in the negative direction. For us this means that good calibration in the positive direction leads to erroneous acceleration measurements in the negative direction. What is the recommended approach to sensitivity calibration of the Z-axis?
Should we use the average? Z_calibration_sensitivity = (Z_sensitivity_positive + Z_sensitivity_negative) / 2
Should we account for 0g offset of the Z axis? Z_calibration_sensitivity = Z_sensitiivty_positive adjusted for Z_0g
Should we treat positive and negative direction separately? This would mean to use Z_sensitivity_positive for positive acceleration samples and Z_sensitivity_negative for negative acceleration samples.
Any other approach that we are yet to consider?