By Steve Leibson Contributed By DigiKey's North American Editors
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The ability to locate the position of any suitably enabled system anywhere on Earth using the Global Navigation Satellite Systems (GNSS) is useful, but there are a few problems associated with using only GNSS receivers for positioning. These problems can be overcome by using inertial measurement units (IMUs) to complement GNSS. This article discusses the embedded use of IMUs, which employ gyroscopes, accelerometers, and magnetometers to measure location based on an initial starting point. It then introduces suitable example solutions and how to use them. How IMUs complement GNSS The problems with GNSS are fourfold. Firstly, GNSS signals are very directional and so can be blocked by buildings. Secondly, receivers have warm and cold startup times measured in the tens of seconds and stretching to one minute or more. This startup time is needed for the receiver to acquire and lock onto the multiple satellite signals required for a position fix.
Thirdly, the GNSS position update rate is limited to once per second. That’s fine for tracking large, slow moving objects, but the startup time is far too long and the update rate is far too slow for many embedded applications. Fourthly, GNSS accuracy is measured in meters, which is too coarse for use in most embedded applications. These applications are as diverse as robotics and virtual reality, which do not involve ground transportation. IMUs provide the finer positioning resolution and faster update rates that are required by many embedded applications. Also, IMUs provide relative position data from a known starting point as opposed to the absolute positioning information from a GNSS receiver, so the two types of position sensors are complementary. Modern electronic IMUs available as board mountable components are based on microelectromechanical systems (MEMS) technology, making them small, light, and relatively rugged. They come with varying capabilities in terms of degrees of freedom (DOF), and unlike GNSS receivers, IMUs do not depend upon radio signals. They also
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