The four acceleration sensors connected to the structure measure absolute acceleration. This means that the
acceleration measurement of the structure is not the acceleration of the structure with respect to the ground,
i.e.,
, but is equal to the acceleration of the structure with respect to a stationary point,
i.e., the floor of the lab. So, the acceleration sensors actually measure
.
The accelerometers used in this experiment make use of a modern sensor technology called MEMS.
MEMS stands for Micro-Electro-Mechanical System. MEMS sensors are made by forming a small mechanical element
on the surface of a semi-conducting integrated circuit. The mechanical element (like a beam) will respond
to its environment and this response is autmatically converted to an electrical signal. A key advantage of
MEMS sensors is that the electronics required to make the signal strong and noise-free are all part of the
same piece of silicon that is used for the sensor. The sensor and the electonics are monolithic.
The accelerometers used in this experiment have an additional feature in that they can measure very low
frequencies with great accuracy ... actually all the way down to 0 Hz. This feature makes MEMS accelerometers
very convenient to use in low-frequency applications (less than 10 Hz). They are also rugged and inexpensive.
In most automotive air-bag deployment systems, the sensor that measures the acceleration of the automobile impact is a MEMS accelerometer.