Choosing an IMU: FOG vs MEMS IMUs

Summary

Improvements in IMU technology have revolutionized the positioning and navigation industry and, with new MEMS gyro sensors reaching better accuracy, the gap between consumer grade micro-electro-mechanical systems (MEMS) gyros and industrial grade fiber optic gyros (FOG) is narrowing. This is a brief description of the key differences between FOG IMUs vs MEMS IMUs and the performance traits between them.

How They Work

FOG-Based IMUs

FOGs use loops of optical fiber and measure interference in beams of light in opposite loops to detect rotation in each axis. The hardware used is more expensive, larger and typically consumes more power but its lack of moving parts makes it less sensitive to temperature changes and mechanical vibration. FOGs are desirable in demanding high temperature, high vibration environments like mining, industrial machine pointing and heavy equipment stabilization.

MEMS-Based IMUs

MEMS sensors are smaller and lighter, but due to their mechanical nature they can be more sensitive to unmodeled temperature and vibration effects. These effects can increase the noise (Angular Random Walk) and cause deviations from the modelled noise figure. For more information on IMU accuracy parameters, please see our related Knowledgebase article.

Benefits of Each

The superior accuracy of a FOG is seen in low bias stability, or drift over time. For applications requiring dead reckoning position updates or experiencing long term GNSS outages, this is a factor and the performance of a FOG gyro is an order of magnitude better than MEMS. On the other hand, if the IMU sensor is only used for short term updates of a GNSS sensor in a well modelled dynamic environment, a MEMS sensor may be all that is needed.

The other appealing factors for a MEMS IMU are size, power and price. Applications like robotics and UAVs hold a premium on payload size and weight, and the latest MEMS sensors are very small and power efficient especially when compared to industrial and tactical FOG IMUS. They can provide excellent position and attitude updates when in relatively stable and predictable dynamic environments, like road vehicles, aircraft and offshore vessels, and the cost is typically less than half of a quality FOG IMU.

How to Choose Between FOG vs MEMS IMUs

In summary, the choice of IMU depends on the application and environment.

FOG IMUs are desirable for:

  • Absolute attitude accuracy
  • High temperature
  • High vibration
  • Bias stability over time

MEMS IMUs are desirable for:

  • Low weight and size
  • Low power consumption
  • Short range pointing sensors
  • GNSS integration in predictable dynamic environments

 

Canal Geomatics offers FOG-based IMUs from KVH and MEMS-based IMUs from Inertial Labs, NovAtel, SBG Systems and Sensonor.

Canal Geomatics remains open.Learn More