Which is g calibration value?

[mbertoni]

Hi to all, which is factory calibration value for g for MEMS accelerometers?

Is this value the same for all accelerometers (I suppose)?

Thanks.

[Eleon BORLINI]

Hi mbertoni, do you mean the LSB to g conversion? It depends on the device (if the output is on 8 bit, 12 bit or 16 bit) and on the FS (the higher the FS, the higer the LSB/g factor). Which device are you using?

[mbertoni]

No, I mean for a generic digital MEMS accelerometer I have (x example) 4096 counts = 1g, but 1g stands for what?

g value changes depending coordinates and altitude, so let's say LIS344AH has been calibrated at ST calibration facility where 1g is 9.7982 m/s^2 while I'm using accelerometer where g is 9.8027 m/s^2.

In this case when I go to read acceleration value in um/s^2 I get wrong values, so I need to know calibration value of g.

[Eleon BORLINI]

Consider that for the analog axl LIS344ALH​ is valid this datasheet sentence:

>> Zero-g level and sensitivity are essentially ratiometric to supply voltage at the calibration level ±8%

This means that 9.8027 m/s^2 - 9.7982 m/s^2 = 0.005 m/s^2 = 0.05% << 0.78m/s^2 = 8%. So you won't be able to detect the difference you wrote. For the sake of completeness, consider also that the lowest gravitational acceleration on Earth (Mount Nevado Huascarán, high and near equator) is at 9.7639 m/s^2, while the highest is at the surface of the Arctic Ocean (low and near pole), at 9.8337 m/s^2, computing a difference of 0.5%, negligible with respect to the sensitivity error.

I suggest you in general to use an average (and typical) 9,81m/s^2 for the g value.

Link: https://www.st.com/resource/en/datasheet/CD00182781.pdf

[mbertoni]

Thanks, but I have to compare processed acceleration data to GPS displacement values and ground velocity values (taken from seismometer) and competitor's devices.

Any further precision (as if < 0.5%) is appreciated.