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Off Indication on wGT3X-BT versus other devices
The Inclinometer feature offers researchers the ability to detect periods of time during which the device
was not worn. For devices other than the wGT3X+, wAc, GT3X+, and Ac, the
inclinometer algorithm makes this prediction by examining the angle at which the device is placed. In
the wGT3X+, wAc, GT3X+, and Ac devices, off detection is performed by analyzing both
the angle at which the unit is placed as well as the length of time the device remains still. Absolute
stillness for three (3) minutes indicates that the unit is likely in an “off” condition regardless of
orientation. As such, epochs that follow three motionless minutes of activity are flagged as “off,” i.e.,
the inclinometer code is equal to zero. These values are not retroactive. That is, the first three minutes
of zero activity are not flagged as “off.” In addition, 30 minutes in the “off” orientation will cause the
inclinometer value to indicate off after that time period has elapsed regardless of motion.
At this time, the inclinometer feature is being validated by the research community.
Low Frequency Extension
The Low Frequency Extension (LFE) option, though not a mode or channel, is another data collection
option during post-processing for the wGT3X-BT. The
Normal
proprietary filter algorithm used in
ActiGraph products is used to eliminate any acceleration noise outside of the normal human activity
frequency bandwidth. This filter is customized to work with ActiGraph’s
The LFE option, when enabled, extends the lower end (baseband) of the filter cutoff, effectively
expanding the bandwidth of the accumulated data. This option is useful when measuring actigraphy
data for subjects who move slowly or take very light steps (for example, the elderly). For more details,
contact ActiGraph at
Data Collection
During initialization, the user chooses the raw data sample frequency (30Hz up to 100Hz in 10Hz
increments). The wGT3X-BT collects data from all on-board sensors in raw data format. Data recorded
includes:
Vertical Axis Activity Acceleration Data (
Axis 1
)
Horizontal Axis Activity Acceleration Data (
Axis 2
)
Perpendicular Axis Activity Acceleration Data (
Axis 3
)
Ambient Light (
Lux
)
Although Steps and Inclinometer are not directly measured during data collection,
these values can be derived from the 3-axis data during *.gt3x file
decompression.
Unlike previous ActiGraph products, the wGT3X-BT does not filter or accumulate data into epochs. Raw
data is collected at the selected sample rate and is post-processed in the ActiLife. Because these devices
collect data from all sensors at all times, users can generate native ActiLife *.agd files containing any
desired combination of parametric data at a later time. This helps facilitate backward compatibility and
