MW8 & MotionWare User Guide: Issue 1.2.1
Page 76
Accelerometer Processing
Raw acceleration measurements are processed by the on-board software of the
MotionWatch to produce a quantitative measure of the activity during each epoch.
This is a four stage process which is applied to the accelerometer data:
1. The channel perpendicular to the watch is separated and subjected to the
bandwidth filtering specified above (3-11Hz).
2. The peak acceleration (either positive or negative) during each second is
recorded.
3.
This is compared to a minimum “not moving” threshold of approximately 0.1g.
Values below this threshold are ignored to simplify the final activity graph.
4. The result from each second is summed over the epoch and scaled to
produce a standard result in controlled jig testing. This value is then recorded
as the MotionWatch count for the epoch.
This process is illustrated in the diagram below, showing the acceleration waveform
over two epochs, each containing two seconds of data.
+35
+40
-25
-30
one second
First 2 second epoch
35 + 40 = 75
Second 2 second epoch
25 + 30 = 55
75 MW counts
55 MW counts
Sensitive in this
direction
