What is an AHRS?
An Attitude Heading and Reference System, better known as an AHRS, is a 3-axis sensor system that provides real-time 3D attitude position – pitch, roll, and heading. The primary function then of an AHRS is to provide orientation data. AHRS are designed to replace traditional gyro-based instruments and to provide superior reliability and accuracy.
Some of the many applications for AHRS include control and stabilization, measurement and correction, and navigation. An example of control and stabilization could be where a camera or antenna mounted on a system such as a plane or ship needs to be stable. Measurement and correction best applies to imaging systems where an AHRS is used to ensure the direction the imager is pointed. And in navigation, an AHRS can be used to provide orientation and direction.
The sensors in AHRS use algorithms to estimate this attitude in 3D space. Some AHRS units will use traditional Kalman filter algorithms that use magnetic and acceleration measurements to estimate the time-varying gyro bias in real-time. Other AHRS systems utilize modified non-Kalman filters that compute an estimation of orientation in real-time. A potential advantage of these modified algorithms is that they can outperform traditional Kalman filter-based sensors by providing real-time optimization of performance for varying magnetic or dynamic operating environments.
AHRS demand very precise gyroscopes as the quality of these devices greatly impacts the overall performance of the inertial sensor system. An example of a very high accuracy gyroscope is a fiber optic gyroscope, commonly known as a FOG. FOGs provide extremely precise rotational rate information due to their lack of moving parts. However, FOGs have a great deal of inherent development and manufacture costs as well as a larger form factor and higher power demands. As technology improves, MEMS-based gyroscopes have closed the performance gap on some FOGs. When factoring in lower cost and power requirements, MEMS-based devices provide an excellent answer for the need of precision in a gyroscope.
MEMS-based Attitude and Heading Reference Systems (AHRS) continue to develop and improve in both technology and application. As the requirements of both military and commercial systems evolve, there is increasing demand for continuous improvement. Both existing systems and those in development must incorporate SWAP-C – Size, Weight, Power, and Cost – standards. Simply put, demand will increasingly require systems and their components to be smaller, lighter, use less power, and all at a lower cost. AHRS are no different in this initiative. Manufacturers must adhere to these principles, all while improving the performance of AHRS. Manufacturers who fail to adjust to these demands will find themselves left behind.