miniAHRS miniature attitude and heading reference system

The miniAHRS miniature attitude and heading reference system (AHRS) is a strapdown, MEMS-based inertial measurement unit with an embedded fluxgate magnetometer from Inertial Labs, a VIAVI Solutions company. It determines absolute orientation (heading, pitch and roll) for any device on which it is mounted, in both motionless and dynamic applications, and is the smallest model in the Inertial Labs AHRS range.

The unit uses three axes each of precision accelerometers, magnetometers and gyroscopes. Integration of the gyroscope output gives high-frequency, real-time measurement of rotation about all three axes, while the accelerometers and the fluxgate magnetometer measure absolute pitch, roll and magnetic azimuth at initial alignment and provide ongoing corrections to the gyroscopes. Kalman-filter-based sensor fusion, gyro-stabilized slaved magnetic heading, embedded 2D and 3D magnetic calibration for hard and soft iron, and full temperature calibration of all sensing elements are part of the design. The algorithms are tuned for the dynamic motion of robots, UAV, UUV, UGV, AGV, ROV, gimbals and antennas, and the unit is suitable as a primary attitude reference.

For an integrator, the key figures are these. Heading accuracy is 0.3° (static, RMS). Gyro bias in-run stability is 2 °/h and angle random walk is 0.38 °/√h, which describe how little the rate output drifts and how noisy it is over averaging time. The gyroscope range is ±2,000 °/s. Accelerometer range is selected by product code, with ±40 g the widest option; on the lowest-range option the accelerometer bias in-run stability is 10 µg and the velocity random walk is 0.02 m/s/√h. The output rate is user settable up to 2,000 Hz. The unit weighs 20 g in a compact case, which suits enclosures with tight space and mass budgets. All components are solid state, with no moving parts.

Electrically, the miniAHRS runs from a 5–15 V DC supply and draws 0.5 W. The communication interface is RS-422, on a 10-pin connector that carries power, RS-422 input and output, a time-of-validity output and an external trigger input, the last two available by request. Output signals include heading, pitch and roll, quaternion, PPS time, accelerations, angular rates, magnetic field, and delta theta and delta velocity. Data is output in binary format, with ASCII available in the GUI. The aluminum case is offered with captive screws or without screws, in both cases mating to a screw-lock connector. Inertial Labs supplies drivers and tools for ROS, LabVIEW and Waypoint products, and a Software Development Kit allows custom processing workflows.

The case is environmentally sealed to IP67 and the unit operates from -40–75 °C. Inertial Labs describes its AHRS family as MIL-STD-810G qualified; confirm that qualification for the miniAHRS with the maker before starting a qualification program.

Typical applications include UAV payload and platform attitude reference, fire control for low-caliber artillery, antenna pointing for line-of-sight and beyond-line-of-sight links, platform and gimbal stabilization, and use on ground, underwater and robotic vehicles. As a strapdown unit, it is lighter, smaller and uses much less power than a gimbaled system.