How to read an IMU datasheet

New to inertial sensors? Start with [What is an IMU?]

The four numbers that decide navigation performance

1. Gyro bias stability, in degrees per hour. The headline. It describes how much the gyro’s zero point wanders during operation, the error that, integrated over time, becomes your heading and position drift. Rough grades: consumer above 10 °/hr, industrial 1 to 10, tactical 0.01 to 1, navigation 0.001 to 0.01, strategic below 0.001. Check how it is quoted. An Allan-variance minimum at constant temperature on a bench is the flattering version. In-run behaviour over temperature is what your mission gets.

2. Angular random walk, in degrees per root hour. The gyro’s noise, and the limit on short-term heading accuracy. Two units with identical bias stability and different ARW behave very differently in the first minutes of an outage, which is often exactly the window you care about.

3. Accelerometer bias stability, in micro-g. Position error grows with the square of time on accelerometer bias. A superb gyro next to a mediocre accelerometer is a mediocre IMU. Anything in the low tens of µg is serious. OSCP’s units run <15 µg across the family.

4. Bias repeatability, turn-on to turn-on. Different from in-run stability: how close the bias lands each power-up. Poor repeatability means long alignment routines before every mission, an operational cost datasheets rarely spell out.

The supporting cast

Scale factor error, in parts per million. How accurately the sensor converts real rotation into output. Matters most on platforms that turn a lot.

g behaviour, in degrees per hour per g. Rotation error created by acceleration and vibration, and the quiet killer on drones and tracked vehicles. This is largely a MEMS problem: vibrating structures read false rotation under g-loading, while optical gyros have no vibrating mass to excite. On vibration-heavy platforms, weigh how the sensing technology behaves under g, not just the bench bias number.

Bandwidth and output rate. Your control loop needs data fast enough. A navigation-grade sensor at 10 Hz cannot stabilise a fast airframe.

Operating temperature, shock and ingress ratings. A unit rated across a real temperature range and sealed against dust and water survives fielding. Lab-only ratings do not. Check which rating applies to which model, because they often differ across a family.

Interface. RS-422 and CAN-FD integrate cleanly on vehicles. Consumer buses may not survive the wiring run.

Traps in plain sight

Best-case footnotes. “0.5 °/hr, Allan minimum, 25 °C, after a 30 minute warm-up” is not 0.5 °/hr in a moving vehicle. Read every footnote attached to the headline spec.

“Up to” specs. A range quoted as its best endpoint. Ask for typical and maximum, and for the test method.

Minimum quoted as the spec. Many datasheets print a Min, a Typical and a Max column, and marketing quotes the Min. Ask which column the number on the web page came from.

No over-environment data. A datasheet showing only 25 °C bench numbers is hiding how the unit behaves across the temperature, shock and vibration your platform actually sees. Ask for it.

Gyro-only pride. A datasheet that whispers about its accelerometers is telling you where the money was not spent.

Silence on export. Jurisdiction and content decide whether you can ship the system you build. See [What does ITAR-free actually mean?]