An accelerometer is an instrument that measures acceleration. It is attached to the surface of the object that will experience the acceleration. As the object moves, it causes an electric current to flow, which measures the amount of acceleration that is taking place and indicates that amount on the calibrated accelerometer.

Accelerometers are used to measure the acceleration on the surface of the body to which they are attached. There are several different accelerometer designs, including: Piezo-electric: Piezo-electric devices are sensitive to changes in the acceleration applied to the element during compression. The charge output of the piezo element varies with the applied acceleration. There are several different internal designs. Piezo accelerometers cannot measure to DC (0 Hz), but can measure to very high frequencies (in excess of 50 kHz). Strain gauge: A mass under load is instrumented using a full-bridge strain gauge. The output of the bridge varies with the applied acceleration. Strain gauge accelerometers can measure to DC, but do not have as high a frequency response as piezo devices (typically under 1 kHz). The transducer may also be fabricated from micro-machined components, often in silicon, rather than tradition mechanical components. These devices usually have a wider frequency response than mechanical transducers and are more rugged. Capacitive: An accelerometer can be built from a capacitive element. In these a mass attached to plates vibrates and the change in capacitance (gap) between these plates is proportional to the applied acceleration. These transducers also measure to DC and are generally more rugged than mechanical strain gauge accelerometers. Servo: An older design, not often used these days except in speciallized applications. A servo accelerometer contains a mass whose position is controlled by a servo feedback mechanism. The feedback signal is proportional to acceleration. Servo accelerometers can be quite fragile, but can measure very low levels of acceleration. They also respond to DC. Accelerometers are used to measure more than vibration. They can be used to measure the angle of the surface to which they are attached, externally applied forces, and they are used in gyro mechanisms.