BT11i High g Accelerometer User’s Guide
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•
Position the accelerometer with the arrow pointing down for the first calibration
point. Define this as -‐9.8 m/s
2
or -‐1.0 g.
•
Rotate the Accelerometer so the arrow points up and use the reading for the
second calibration point. Define this as 9.8 m/s
2
or 1.0 g.
The accelerometer will read 0.0 m/s
2
or 0.0 g when it is held horizontally.
Suggested experiments
The Accelerometer can be used for a wide variety of experiments, both inside and
outside the classroom. The Accelerometer should be mounted in the appropriate
orientation for an experiment (so that its axis is in the direction of interest).
•
Measuring acceleration during a collision.
•
Measuring acceleration as it moves in a horizontal circle and/or vertical circle.
•
Measuring accelerations during body movements: put the Accelerometer under
your belt buckle, and jump up and down, land both with your knees flexed and
with your knees held more stiff.
•
If you have the CMA VinciLab data-‐logger you might measure acceleration on
elevators, on amusement park rides, on playground apparatus, in a car, during
bungee jumps, etc.
•
To measure acceleration in two or three directions mount two or three
Accelerometers at right directions.
DO NOT
drop the sensor directly onto a solid surface this will damage the sensor.
Interpretation of Accelerometer measurements
An accelerometer is an electromechanical device that measures acceleration forces.
Such forces may be static, like the constant force of gravity, or, as is the case with
many mobile devices, dynamic to sense movement or vibrations.
Also the CMA High g Accelerometer is sensitive to both, movement acceleration and
the Earth’s gravitational field and interpreting its measurements is complex.
The accelerometer does not measure gravity; it actually measures "non-‐
gravitational" acceleration -‐ the component of "total acceleration minus gravity"
along its input axis. This is the acceleration it experiences relative to free fall.
The basic principle of operation behind the accelerometer is the displacement of a
small proof mass, which is attached to the case with a spring that deflects in
proportion to the force applied to the proof mass. When the device is in rest the
constant gravity force is acting on the proof mass. The only measured acceleration is
on this moment the acceleration due to gravity. As acceleration is applied to the
device, consistent with Newton's second law of motion (F = m*a) an additional force
proportional to the applied acceleration develops. The accelerometer output is
proportional to the net acting force and to acceleration of the proof mass.
