Vibration is a disturbance that is put onto a system. Causes of vibration can be categorized as: continuous, impulsive, and intermittent.
Accelerometers (made of piezoelectric material) are used to measure vibration. Accelerometers gives off a small voltage when they are moved. This voltage is magnified and processed by a signal analyzer – generally in a computer. The system is calibrated using a shaker. Calibration is performed by connecting the accelerometer to a calibrated shaker that moved up and down at a specific frequency and amplitude.