Data Sheet

October 2017 BNO080 Datasheet 1000-3927

3 Calibration and Interpretation

The BNO080 interprets the data from its sensors to model the device’s motion and ultimately determine the

device’s orientation and classify the motion of the device. The accuracy of this model is dependent on the quality

of the data provided by the sensors.

All sensors exhibit slight imperfections. These imperfections generally appear as errors in offset and scale.

Sensor systems that contain three axes have an additional variant of offset that includes skew and rotation (skew

is the non-orthogonality of the three axes and rotation is the angular difference of the coordinate frame of the

sensor to the coordinate frame of the device). Calibration of the sensor data falls into two categories:

• Static calibration

• Dynamic calibration

Static calibration is the correction of non-varying parameters to the data returned from the sensors. These static

adjustments to the data typically compensate for offsets and scaling errors that do not vary over time or with

temperature. Examples (this list is not exhaustive) of non-varying errors (or errors that are not compensated for

dynamically) are:

• Accelerometer (or gyroscope or magnetometer) skew (also called cross-axis sensitivity)

• Accelerometer (or gyroscope or magnetometer) gain or sensitivity

• Sensor orientation with respect to device frame of reference

A static calibration data record (SCD) is essentially a description of the sensor system used on the device and

from that record the BNO080 calibrates and interprets the data from the sensors producing data in the appropriate

SI units for use by applications. The SCD record can be generic and essentially describe the sensors as per the

datasheet, or the record can be specific to the actual sensors in the package.

A calibration record derived from the specific sensors populated on the device is a more accurate description of

the actual sensors used and will hence yield a more accurate model of the device’s motion. Hillcrest provides a

calibration system (CTS3) that when used in the production facility with suitable motion inducing equipment can

evaluate the individual sensors on the device and build the appropriate SCD record for that device. More details

on CTS3 are available on request.

Dynamic calibration is the correction to the data returned from the sensors that varies with either time or

temperature. The BNO080 calculates what the adjustment should be during use of the sensor and applies

correction factors as necessary in real time. Examples of dynamic calibration parameters are:

• Gyroscope zero-rate offset

• Accelerometer zero-g offset

In addition as the BNO080 has applications in devices such as Robot Vacuum Cleaners it is necessary to

calibrate the accelerometer in a planar fashion (i.e. around the axis that the vacuum cleaner revolves). Selection

of 3D or planar accelerometer calibration is via command.

Magnetic field calibration is an additional capability of the BNO080. The primary goal of using the magnetometer

is to measure the Earth’s magnetic field. The magnetic field measured by a magnetometer is distorted by the

presence of ferrous and magnetic material in the near vicinity. These distortions are referred to as soft and hard

iron effects respectively. The offset and distortion to the measured magnetic field is estimated and compensated

for continuously while the device is in motion. Removal of the distortions allows for an improved estimate of the

Earth’s magnetic field.

3.1 Calibration Effects

This section provides a brief overview of the benefits of dynamic calibration and the recommended settings for

various applications.