ADAFRUIT PCB extension board : Datasheet : Page 8

Calibration and Programming

Static Calibration:

As with all sensors, there is some variation in output between samples of these

accelerometers. For non-critical applications such as game controllers, or simple motion or tilt

sensors, these variations are not important. But for applications requiring precise

measurements, calibration to a reliable reference is a good idea.

Gravity as a Calibration Reference

Acceleration is measured in units of gravitational force or "G", where 1G represents the

gravitational pull at the surface of the earth. Despite what you may have

heard (http://adafru.it/aRE), gravity is a pretty stable force and makes a convenient and

reliable calibration reference if you happen to be a surface-dwelling earthling.

Calibration Method:

To calibrate the sensor to the gravitational reference, you need to determine the sensor output

for each axis when it is precisely aligned with the axis of gravitational pull. Laboratory quality

calibration uses precision positioning jigs. The method described here is simple and gives

surprisingly good results.

For High-G accelerometers such as the ADXL377, the +/- 1G range of static

calibration is too small to assure good accuracy over the +/- 200G range of the

sensor.

Accurate calibration for extreme G-forces requires more specialized

equipment to repeatably create these extreme forces in a controlled environment.

One commonly used technique is to drop the accelerometer from a known height

and measure the negative acceleration at impact.