MEMS technology is really robust against shocks, but they can be more or less sensitive to vibrations, especially high frequency ones.
SBG Systems has designed inertial sensors with a special care on signal processing, using only high quality MEMS sensors, combined with efficient anti aliasing FIR filters to limit vibration issues as much as possible.
Nevertheless, special attention on user side is sometimes required in highly vibrating environments.
Effect of vibrations on inertial sensors
High amplitude vibrations can cause a bias in accelerometer reading. Thanks to our superior factory calibration, this effect can be limited. Nevertheless it cannot be fully avoided . This effect is called the VRE (Vibration Rectification Error) and comes from the internal accelerometer non-linearity.
Depending on its technology, the gyroscope can also be affected by vibrations, and added noise or bias can be observed when applying vibrations, but the accelerometer is the limiting factor in most cases.
In addition, very high frequency vibrations can also affect the MEMS sensors, due to their resonant frequency, most of the time in the range of a few KHz. If frequencies higher than 1KHz present, those vibrations must be taken into account. Hopefully, these high frequency are most of the time easy to handle.
Tests against vibrations
At SBG Systems, we specify all our sensors to a certain level of vibrations. These specifications have been validated using a shaker.
The test method we use is the MIL-STD-810G minimum integrity figure shown below:
Consequences of highly vibrating environment
Depending on vibrations strength, consequences can range from a slight orientation offset, to a completely wrong output.
It's quite easy to test if vibrations are disturbing the sensors, just let the device steady and apply vibrations:
The sensors provide many status outputs that can be used to see if vibrations are disturbing the device: The status flags should be in a valid state more than 80% of time in normal operating conditions. This status flags can be monitored while in motion.
In addition, all SBG Systems sensors provide accuracy indicators that can also be used to check if a reasonable accuracy is available in most situations.
Another way is to maintain the system stationary and apply vibrations by turning off the engines or other vibrations sources. Then it's possible to monitor the accelerometers and gyroscopes to test if any drift is observable. Euler angles should also be stable as long as the device is stationary.
Solutions against vibrating environment:
- Physically damp vibration (with appropriate material, for instance Silent Bloc)
- When dealing with a low weight sensor (for instance IG-500), it might be necessary to damp the sensor together with a heavier mass (like a battery) to damp vibrations more easily. It is always easier to isolate a heavier system from vibrations.
- Use flexible cables to avoid transmitting vibrations through the cables.
- In case of high frequency vibrations, check if the vibrations are propagated by the air (sound) and isolate the device accordingly with sound absorbing materials.
- Use higher range accelerometers, such as 18g instead of 5g