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Document MT0605P.2018.E
© Xsens Technologies B.V.
MTi User Manual
“
Modeling Parameters
” are the values that describe the conversion from the physical phenomenon to
a digital output in an orthogonal coordinate system:
Offsets
(bits): Digital reading in bits of the sensor when no physical signal is measured. The barometer
is a digital sensor and does not require calibration, hence the value is always 0.
Gain
(bits): Gains (or scale factor) describe the relation between the digital reading in bits and the
measured physical signal. The barometer is a digital sensor and does not require calibration, hence the
value is always 0.
Alignment matrix
: Non-orthogonality of the sensor triad. This includes non-orthogonality in the
orientation of the sensitive system inside the MEMS sensor, the mounting of the sensors on the PCB of
the MTi, the mounting of the PCB’s and the misalignment of the OEM board in the MTi housing.
The “
Basic test Report
” describes the noise of the all internal sensors (note: barometer noise is not
determined in the MTi Mk5 and is therefore always 0). Furthermore, it shows the Test & Calibration
date and who performed the test and calibration.
Next to the basic Test and Calibration values shown in MT Manager, each device is calibrated according
to more complicated models to ensure accuracy (e.g. non-linear temperature effect, cross coupling
between acceleration and angular rate
6
).
5.8 Sensors data outputs
5.8.1 Physical sensor model
This section explains the basics of the individual calibration parameters of each MTi. This explains Test
and Calibration parameters in MT Settings (see also 5.7).
The physical sensors inside the MTi (accelerometers, gyroscopes and magnetometers) are all calibrated
according to a physical model of the response of the sensors to various physical quantities, e.g.
temperature. The barometer and GNSS receiver do not require calibration. The basic model is linear
and according to the following relation:
𝑠 = 𝐾
𝑇
−1
(𝑢 − 𝑏
𝑇
)
From factory calibration each MTi has been assigned a unique gain matrix,
K
T
and the bias vector,
b
T
This calibration data is used to relate the sampled digital voltages,
u
, (unsigned integers from the 16 bit
ADC’s) from the sensors to the respective physical quantity,
s
.
The gain matrix is split into a misalignment matrix,
A
, and a gain matrix,
G
. The misalignment specifies
the direction of the sensitive axes with respect to the ribs of the sensor-fixed coordinate system (
S
)
housing. E.g. the first accelerometer misalignment matrix element
a
1,x
describes the sensitive direction
of the accelerometer on channel one. The three sensitive directions are used to form the misalignment
matrix:
𝐴 = [
𝑎
1,𝑥
𝑎
1,𝑦
𝑎
3,𝑧
𝑎
2,𝑥
𝑎
2,𝑦
𝑎
2,𝑧
𝑎
3,𝑥
𝑎
3,𝑦
𝑎
3,𝑧
]
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Also known as “g-sensitivity”.
