Hi everyone,
I've been trying to figure out accelerometer and gyroscope
calibrations, and am a bit confused at what I've been reading. I have
a set of SHIMMER2R with gyroscope board, so the MEMS that are onboard
should be the accelerometer MMA7361L and the gyroscope IDG500, right?
A few questions:
1) I was reading though the Shimmer_AccelCalibration document, and the
document cites the datasheet for the MMA7260Q, which is different than
the ones on the SHIMMER2R. Does the scaling values cited in this
document, particularly 744 (for sensitivity) and 372 (conversion to g)
still apply to the MMA7361?
2) The equation provided in Shimmer_AccelCalibration, to convert ADC
units to units of g, is:
[1] sensitivity_error * (measured_value - calculated_midpoint) / 372
In an ideal case, this equation would be (measured_value - 2048)/372
However, looking at Section 9.1 of Shimmer User Manual 2Rc, for 1.5g,
my ideal equation is
[2] (measured_value - 2048) / 993
Evidently, these two equations would return different values. Which
equation should I be following? I was using the eq'n [2], which
appears to be correct, and just assuming my system is ideal, but now
would like to account for the calibration errors in my devices. Should
I just take eq'n [1] and replace 372 with 993?
3) Looking at the tables in the MMA7361 and MMA7260, the sensitivity
values are different than that reported in the table in Section 9.1. I
can see that the Section 9.1 table is just the reported table rescaled
from 3.3V to 3.0V. Can we assume that the SHIMMER2R is able to provide
a constant 3.0V? Though, I suppose the calibration techniques outlined
here would correct for the voltage scaling.
4) Lastly, I was wondering if there are documented methods on
gyroscope calibration? A search online tells me that the best way to
do this is to find a turntable and basically do the same +g/-g
procedure as is with the accelerometer. Are there other methodologies
out there, or should I just focus on obtaining a turntable or a motor
of some sort?
Thanks in advance.
-Jonathan
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