An inertial measurement unit or IMU is a device that can measure and report an object’s specific angular rate, specific force, and sometimes the orientation. Such devices use an accelerometer to measure an object’s specific force, a gyroscope to measure the object’s angular rate, and sometimes a magnetometer to measure the earth magnetic field . IMU acts as the main sensor for an inertial navigation system which captures data about the system’s movement, converts the output of the inertial sensor to engineering units, and transmits those outputs to a data bus. This article will examine the components of IMUs, and its applications, as well as the relevant information required for selecting an appropriate IMU based on the application.
An IMU consists of multiple sensors including accelerometers, gyroscopes, and in some cases, a magnetometer. Most accelerometers measure the specific force along a single axis, and most gyroscopes measure the angular rate along a single axis. An IMU typically combines multiple accelerometers and gyroscopes to measure the angular rate and specific force along three axes. This allows a three-dimensional measurement of angular rate and specific force. Some devices also include a magnetometer to measure the magnetic field.
IMUs can vary in cost, size, and performance. Typically, the more massive an IMU is the higher the performance will be, and therefore the more costly the unit becomes. Current technology for lower cost inertial sensors is based on the use of microelectromechanical systems (MEMS) technology.
A MEMS sensor allows for the low-cost mass production of light and small quartz or silicon sensors. This is done through etching techniques with numerous sensors on a single wafer. Not only are MEMS-based IMUs more affordable than conventional mechanical and optical designs, but they also can have significantly smaller size which is desirable in applications such as UAV and drones. The affordability of MEMS-based IMUs has made them a popular choice for many applications such as for XYZ producers in which lowering production cost is critical.
IMUs can be grouped into several performance categories, included but not limited to: marine, aviation, intermediate, tactical, industrial and consumer. The highest grade of IMUs is marine-grade, followed by aviation-grade, intermediate-grade, tactical-grade, industrial-grade, and consumer grade in descending order
The highest grade of IMUs is marine-grade, followed by aviation-grade, intermediate-grade, tactical-grade, industrial-grade, and consumer grade in descending order. The performance of an IMU is dependent upon the extent of its calibration and processing. The term “low-cost” MEMS-based technology refers to tactical, industrial or consumer grade IMUs, although the price range of this technology can vary greatly. Many consumer-grade MEMS-based IMUs are sold without calibration, however tactical-grade and industrial-grade IMUs are sold with calibration.
The table below summarizes the performance-grades, cost, and applications of IMUs:
| Grade | Cost | Application |
| Marine | $1 million | Military ships, submarines, intercontinental ballistic missiles, and spacecraft |
| Aviation | ~$100,000 | Military ships, submarines, intercontinental ballistic missiles, and spacecraft |
| Intermediate | $20,000-$50,000 | Small Aircraft and Helicopters |
| Tactical | $2,000-$30,000 | GPS compensation used in guided weapons and UAVs |
| Industrial | $500 to $2,000 | Robotic, drones, agriculture and construction |
| Consumer | ~$10 | Smartphones, Pedometerspedometers, and antilock braking systems (ABS) |