18
UM001
3.1.1
Magnetometer
Magnetometer IMU Measurements
3.1.2
Accelerometer
Accelerometer IMU Measurements
3.1.3
Gyro
Gyro IMU Measurements
3.1.4
Raw IMU Measurements
The raw IMU measurements are collected from the internal MEMS at the highest rate available for each
individual sensor. For the gyro and accelerometer, the measurements are down-sampled to the IMU Rate.
3.1.5
Factory Calibration
Each VN-100 sensor is tested at the factory at multiple known angular rates, accelerations, and magnetic
field strengths to determine each sensor’s unique bias, scale factor, axis alignment, and temperature
dependence. The calibration coefficients required to remove these unwanted errors are permanently
stored in flash memory on each sensor. At the IMU Rate, these calibration coefficients are applied to the
raw IMU measurements, to correct for and remove these known measurement errors. For thermally
calibrated units the onboard temperature sensor is used to remove the measurement temperature
dependence. The output of the factory calibration stage is referred to as the calibrated (but un-
compensated) IMU measurements.
Raw
Magnetometer
Data
Factory
Calibration
External
Magnetometer
Data
User
Magnetometer
Compensation
(Register 23)
User Reference
Frame Rotation
(Register 26)
User Low-Pass
Filtering
(Uncompensated)
(Register 85)
Onboard Hard/
Soft Iron
Compensation
(Register 44+47)
Uncompensated
Magnetometer
(uncompMag)
Compensated
Magnetometer
(magBody)
User Low-Pass
Filtering
(Compensated)
(Register 85)
Raw
Accelerometer
Data
Factory
Calibration
User
Accelerometer
Compensation
(Register 25)
User Reference
Frame Rotation
(Register 26)
User Low-Pass
Filtering
(Uncompensated)
(Register 85)
Uncompensated
Accelerometer
(uncompAccel)
Compensated
Accelerometer
(accelBody)
User Low-Pass
Filtering
(Compensated)
(Register 85)
Accelerometer
Filter Bias
Compensation
Raw Gyro Data
Factory
Calibration
User Gyro
Compensation
(Register 84)
User Reference
Frame Rotation
(Register 26)
User Low-Pass
Filtering
(Uncompensated)
(Register 85)
Gyro Filter Bias
Compensation
Uncompensated
Angular Rate
(uncompGyro)
Compensated
Angular Rate
(angularRate)
User Low-Pass
Filtering
(Compensated)
(Register 85)