AHRS Attitude Heading Reference System

An AHRS, sometimes wrongly called IMU, provides 3D orientation by integrating an inertial gyroscopes. Using accelerometers and magnetometers, integration drift is compensated for by reference vectors, namely gravity and the earth magnetic field. This results in a drift-free orientation, making an AHRS a more cost effective solution than conventional high-grade IMU’s, that only integrate gyroscopes and rely on a very high bias-stability of the gyroscopes.

Affordable MEMS AHRS’s

Affordable MEMS AHRS’s were introduced just after 2000, when inertial sensors prices dropped and accuracy improved, to enable the mass introduction of ESP, airbags and built-in car navigation. The improved inertial sensors were used by companies such as Xsens to design AHRS’s that provide 3D orientation for a broad range of applications from human motion to navigation of unmanned vehicles and the stabilization of antenna and camera systems. A proven product is the Xsens MTi-10, miniature AHRS and MTi-100 AHRS.

Kalman filtering

Using gyroscopes, accelerometers and magnetometers does not yet provide a stable orientation. In order to cope with transient accelerations, magnetic disturbances and vibrations, it is needed to fuse the data of all sensors in a Kalman filter. The Kalman filter can be tuned in different ways, depending on the application where the AHRS is used in. To accommodate the best performance, Xsens offers user scenarios that are specifically tuned for the customer’s application.

GPS enhanced AHRS’s

To improve the AHRS performance under long-lasting accelerations and under conditions with severe magnetic disturbance, Xsens has launched the MTi-G GPS enhanced Motion Tracker. The MTi-G uses GPS to determine accelerations and velocity, which can be used to make the referencing with gravity more robust, resulting in a robust roll and pitch. Using the heading and course of the GPS, it is also possible to retrieve heading without using the magnetometers.

The MTi-G is often used in applications that are high-dynamic. Test results and testimonials can be found here:

MEMS AHRS’s as a replacement for high-grade IMU’s?

The world of orientation sensing has long been dominated by high-grade IMU’s, commonly used in ships (notably submarines), aircraft and ground defense applications. The price of these high-grade IMU’s (e.g Honeywell, Sagem, Northrop Grumman/Litef IMU’s) were prohibiting the use of orientation sensors in the smaller scale applications, such as antenna stabilization, small unmanned vehicles and remotely operated submarines (ROV’s). The current state of technology in MEMS AHRS’s makes it possible though to replace expensive IMU’s with these intelligent MEMS AHRS’s in selected applications. It also makes the use of orientation sensors possible where an orientation sensor had not been considered before. A few examples can be found at the Xsens website:

• Stabilizing an antenna for EM Solutions; EM Solutions provides a stabilized antenna system in challenging, mission-critical environments. The accuracy of the Xsens MTi-G is sufficient to cope with vibrations and dynamic movements.
• MTi’s steering a fleet of robots; the number of robots in a fleet (6 or more) makes the use of conventional orientation sensors very expensive. Using MTi’s gives the fleet manager information on every single robot.

> Request a quote for MTi-10
> Request a quote for MTi-100
> Request a quote for MTi-G-700

Wambots with MTi AHRS