An Introduction to Accelerometers

Using Sensors to Measure Acceleration

May 23, 2008 Susan Kristoff

Accelerometers allow engineers to measure the accelerations in bodies and systems to ensure safety and proper operation, but can also be found in everyday objects.

An accelerometer is one of many types of sensors. In this case, the physical property being measured is acceleration. Acceleration is defined as the rate of change of velocity of an object or point on an object. Acceleration can be linear, along a straight path, or angular, such as in a spinning object. An accelerometer can also measure the effect of gravity, which results in a reading of 1g (9.81 m/sec^2) in the vertical direction on Earth. Accelerometers are available in various ranges, from very low frequencies to extremely high frequencies.

Types of Accelerometers

There are many different types of accelerometers. The most commonly used types include:

• Piezoelectric – Piezoelectric accelerometers consist of a mass and a piezoelectric component. When the accelerometer is subjected to acceleration, the mass pushes against the piezoelectric component, creating an electrical charge. This charge is proportional to the input acceleration.
• MEMS – Accelerometers that use micro-electrical manufactured systems (MEMS) use one of the simplest MEMS structures: a cantilever beam with a proof mass on the end of the beam. Deflection of the beam is measured and is proportional to the amount of acceleration.
• Capacitive – Capacitive accelerometers are also MEMS structures that use a spring/mass combination. Changes in the distance between the two plates of the capacitor are proportional to the acceleration input.

Since accelerometers can only measure acceleration in one axis, often multiple accelerometers are combined to measure acceleration in two or three dimensions simultaneously. Three-dimensional accelerometers can be used to fully characterize the translation of a body through three-dimensional space.

Uses for Accelerometers

Accelerometers are a valuable resource for engineers who test objects and systems. Anthropomorphic test devices, more commonly known as crash test dummies, incorporate several accelerometers to determine how events and accidents would affect the human body. Accelerometers monitor seismic activities and other low-level vibrations.

Accelerometers may be used by engineers for testing, but they can also be found in many every day locations. The most widely used application for accelerometers is automobile airbag systems. Airbag systems contain accelerometers that trigger airbag deployment when a specified threshold is reached. Other applications include the Nintendo Wii game system, which uses accelerometers to translate the motion of the controller to motion within the video game. Some pedometers incorporate accelerometers to measure the wearer’s steps.

Accelerometers are sensors that provide engineers with useful data about the behavior of objects and systems, and enrich the daily lives of people that use devices that contain accelerometers. To learn more about other types of sensors, please read the article An Introduction to Sensors.

Sources

PCB Electronics website

Omega Engineering website

Nintendo website

The copyright of the article An Introduction to Accelerometers in Engineering is owned by Susan Kristoff. Permission to republish An Introduction to Accelerometers in print or online must be granted by the author in writing.

An accelerometer.

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