What rate and range settings are appropriate?
The accelerometer has configurable sample rates, adjustable sensitivity and a low power mode. The sample rate affects both the maximum sampling period and the battery life. Higher sample rates reduce the amount of time the device can record for and use extra battery power during recording. The accelerometer has a low power mode to reduce the current consumption and increase battery life, this setting increases the amount of noise present on the accelerometer output and may not be suitable for high precision applications. The device is designed to sample for at least 2 weeks on a full battery charge at 100 Hz in the full power mode. The table below shows how adjusting the sample rate will affect the battery.
|Sample Rate (Hz)||Normal Battery Life (days)||Low Power Battery Life (days)|
The accelerometer has a variable sensitivity to allow it to be used in many applications. The selectable ranges are +/- 2 g, +/- 4 g, +/- 8 g and +/- 16 g (g is the acceleration due to gravity or ~9.81ms-2). The user should experiment with these ranges to trade off sensitivity against dynamic range. Accelerations outside the selected dynamic range result in saturation (clipping) of the recorded acceleration. The dynamic range of the accelerometer has no effect on the battery life or memory constraints. Table 2 shows a typical use case for each of the available sensitivities.
|Sensitivity||Example Use Case|
|±2g||Fine movements such as hand writing or painting|
|±4g||Fine movements such as hand writing or painting|
|±8g||Moderate activities such as sprinting, jumping|
|±16g||Severe activities such as boxing|