An attitude and heading reference system (AHRS) consists of sensors on three axes that provide

attitude Attitude may refer to: Philosophy and psychology * Attitude (psychology), an individual's predisposed state of mind regarding a value * Metaphysics of presence * Propositional attitude, a relational mental state connecting a person to a pro ...

information for aircraft, including

roll Roll or Rolls may refer to: Movement about the longitudinal axis * Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis ** Roll (aviation) ...

, pitch, and yaw. These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity) sensors and consist of either solid-state or microelectromechanical systems (MEMS) gyroscopes,

accelerometers An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...

and magnetometers. They are designed to replace traditional mechanical

gyroscopic A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...

flight instruments Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with data about the flight situation of that aircraft, such as altitude, airspeed, vertical speed, heading and much more other crucial information in f ...

. The main difference between an Inertial measurement unit (IMU) and an AHRS is the addition of an on-board processing system in an AHRS, which provides attitude and heading information. This is in contrast to an IMU, which delivers sensor data to an additional device that computes attitude and heading. With

sensor fusion Sensor fusion is the process of combining sensor data or data derived from disparate sources such that the resulting information has less uncertainty than would be possible when these sources were used individually. For instance, one could potentia ...

, drift from the gyroscopes integration is compensated for by reference vectors, namely gravity, and the

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic ...

. This results in a drift-free orientation, making an AHRS a more cost effective solution than conventional high-grade IMUs that only integrate gyroscopes and rely on a high bias stability of the gyroscopes. In addition to attitude determination an AHRS may also form part of an

inertial navigation system An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dir ...

. A form of non-linear estimation such as an

Extended Kalman filter In estimation theory, the extended Kalman filter (EKF) is the nonlinear version of the Kalman filter which linearizes about an estimate of the current mean and covariance. In the case of well defined transition models, the EKF has been considered t ...

is typically used to compute the solution from these multiple sources.AHRS – OpenPilot Project
AHRS is reliable and is common in commercial and business aircraft. AHRS is typically integrated with electronic flight instrument systems (EFIS) which are the central part of glass cockpits, to form the primary flight display. AHRS can be combined with air data computers to form an Air data, attitude and heading reference system (ADAHRS), which provide additional information such as airspeed, altitude and outside air temperature.

References

{{Flight instruments Aircraft instruments Avionics

See also

References