Why are accelerometers used as vibration sensors

The most economic and versatile sensor for vibration measurements is the accelerometer. On rotating machinery these measure the radial forces on shafts and bearings. As the machine rotates a sensor fixed to the machine experiences a force on each revolution pushing or pulling it depending upon the orientation of the machine shaft. As the machine runs, a periodic vibration is observed at the sensor. The output of the sensor can be used to analyse the intensity and frequency of these vibrations which are a measure of the condition of the machine.

On moving objects, such as vehicles, or large structures such as tall buildings, towers or bridges, acceleration will not be periodic or, if so, it will be at very low frequency. In this case an accelerometer will still yield valuable data on the magnitude and time over which the forces are experienced or exerted.

Artificially created ground and building vibrations experienced during building, blasting, drilling or piling activities can also be sensed by accelerometers but as the vibrations are usually random the data must be acquired and analysed in quite different ways to allow sensitive vibration logging.

Natural ground vibrations, earthquakes and tremors are also detected by accelerometers built into measuring systems known as seismographs. Natural ground vibrations have long periods and generally require much higher sensitivities than machine vibration measurements.

Shocks, such as experienced in crash, gunnery and explosive tests can also be measured by accelerometers though in this case there is usually a sudden deceleration at vehicle impact or acceleration at projectile release. The signal is transient over small fractions of a second but will be of very high magnitude. Sensors with very low signal filtering and optimized electronics are needed for this.