SAE2020 Inertial Measurement Unit (IMU) Interface Requirements for Military and Aerospace Vehicle Applications

SAE International, founded as the Society of Automotive Engineers, is a not-for-profit organization that develops and publishes standards used for the aerospace, automotive, and commercial vehicle industries. The standard, “SAE2020 Inertial measurement unit (IMU) interface requirements for military and aerospace vehicle applications,” developed by this organization, describes the inertial and health monitoring data interface requirements for inertial measurement units used in military and aerospace vehicle applications.

An inertial measurement unit (IMU) is an electronic measurement that measures and reports acceleration, orientation, angular rates, and other gravitational forces. These devices consist of 3 accelerometers, 3 gyroscopes, and 3 magnetometers, depending on the orientation requirement. One per axis for each of the three instrument axes: roll, pitch, and yaw.

There are different types of IMU sensors. IMU technology, based on micro electro-mechanical systems technology, allows for lower costs and lower power requirements while providing performance. Systems based on this technology therefore combine high performance and ultra-low power in a smaller unit.

Depending on the rating of the IMU sensor, the main applications include control and stabilization, navigation and correction, or measurement and testing. However, typical measurement unit markets are unmanned system control, mobile mapping applications whether land, air or sea, and any payload requiring stabilization or pointing.

Due to their good performance/size ratio, IMUs are ideal for all unmanned markets, whether it concerns unmanned ground vehicles, unmanned aerial vehicles (UAVs) or unmanned sea vehicles. Tactical and navigation-class IMUs are one of the main components of equipment used in aircraft or ships, missiles and even satellites.

An inertial measurement unit works by detecting linear acceleration using one or more accelerometers and rotational velocity using one or more gyroscopes. Some also include a magnetometer, which is often used as a heading reference.

Physical limitations restrict IMUs to work in certain applications. A wide range of standard specifications and the performance they define must be reviewed to ensure that an IMU is selected that meets the application requirements. Common IMU specifications include range, resolution, bandwidth, and sampling rate. Range is defined as the minimum and maximum input values ​​that a sensor can measure. Anything outside of the range is not measured or output by the sensor. The most precise measurement that can be made over the range of a sensor is known as resolution. In general, this specification is not very important because most sensors in use today have high resolution. Bandwidth is the maximum frequency to which a sensor or system will respond. This frequency is usually defined as the point at which the response is at half power. Bandwidth not only defines the frequencies that a sensor can measure, but is also inversely proportional to the time constant of the analog sensor response. Sensors with higher bandwidth respond more quickly to a given stimulus, and this rise time is the first component in calculating the total system latency. Sampling rate is the number of samples per second that a sensor can output. Although sometimes used interchangeably with bandwidth, sampling rate differs in that bandwidth can be any specified rate while dependent on sensor or system response.

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