Vibration Detector based on GMR Sensors

Up to now, vibrations have been mostly sensed by measuring displacement, velocity and acceleration. The most common types of vibration sensors are piezoelectric, capacitive, null-balance, strain gage, optoelectronic, resonance beam or piezoresistive. We present a low cost and low power vibration detector based on the measurement of magnetic field variations induced in a recent SS501 GMR magnetic sensor, which has never been applied for that. Vibrations on small ferromagnetic pieces disturb the Earth's magnetic field. These weak perturbations can be detected and measured over the assumed constant Earth's magnetic field, which is uniform over a wide area. A novel array configuration of 3 half bridge GMR sensors powered in chain is used to measure magnetic field variations in X, Y, and Z axes with a very low power consumption. This paper includes a characterization of the novel GMR sensors, and describes the practical design and implementation of our vibration detector. As an example it is measured the rotating speed of a small drilling machine and its vibrations at different speeds (rpm). The results are shown and discussed.