Accuracy of IIS3DHHC

[htamas]

IIS3DHHC When used as an inclinometer, what is the minimum angular resolution?

Posted on June 08, 2018 at 23:30

The IIS3DHHC is a triaxial accelerometer that outputs 16-bit data, 3-axis, �2.5 g acceleration data.

So (5g)/(2^16 bits) = 7.63*10^-5 g's/LSB.

arctan(7.63*10^-5) is essentially the same thing (small angle approximation in radians)

and that converts out to 0.00437 degrees -- which is about 0.2622 arc-minutes -- which is about 15.74 arc-seconds.

So the LSB represents about 16 arc-seconds of resolution -- is that correct?

The other way I can talk myself into a solution is to eliminate 1 bit for the sign -- leaving 15 bits for a full scale value. As an inclinometer, I'd never expect the value to exceed 1g -- so now we're down to 14 bits corresponding to 1g.

arctan(1/10^14)=12.5 arcseconds.

At the same time, I see that there is a 2%FS non-linearity -- thats 10-11 bits of data. Where is the deviation the greatest, and how does that affect the usefulness of this device as an inclinometer? By my count -- I'm down to 3-4 bits of reliability.

Thanks,

Mark

[Eleon BORLINI]

Hi @htamas​ ,

>> So the LSB represents about 16 arc-seconds of resolution -- is that correct?

Your theoretical calculation is correct, and the LSB corresponds to the minimum acceleration detection and, consequently to the minimum angular resolution (provide that the integration over time is stable). Ok to consider only half of the FS dropping the sign bit.

>> At the same time, I see that there is a 2%FS non-linearity -- thats 10-11 bits of data. Where is the deviation the greatest, and how does that affect the usefulness of this device as an inclinometer?

The maximum accelerometer nonlinearity is for acceleration near or above the FS (not this case, for a tilt measure the maximum acceleration is 1g < FS), or for fast varying accelerations (not this case, the inclinometer frequency range of interest is the very low spectrum)

Regards