ActiGraph ACTITRAINER Uživatelský manuál stáhnout pdf (Strana 15)

15 | Page

15 W. Main St. Pensacola, FL 32502 tel 850.332-7900 fax 850-332-7904

Steps

Step counts are accumulated on a per-epoch basis and are based on accelerometer data collected on Axis 1 (the vertical

axis). An algorithm present in the device firmware filters out the accelerometer’s baseline noise level to help accurately

accumulate the steps-per-epoch.

Inclinometer

The inclinometer feature can help users identify the orientation of the device and, more importantly, when the device

itself was taken off. Each epoch is flagged with a number (1 through 4) to indicate the orientation of the device during

that epoch. For GT3X+ devices, this is done when converting the *.gt3x file to *.agd format. As noted, the inclinometer

feature is only valid when the device is worn vertically on the point of the hip. More details are available in the

Inclinometer Whitepaper.

Important The inclinometer feature is only valid if the device is worn on the hip with Axis 1

upward facing.

Inclinometer Code

(Stored with each Epoch)

Interpretation

0 Device Off (Not Being Worn)

1 Subject Standing

2 Subject Lying Horizontal

3 Subject Sitting

Table 1 - Inclinometer Definitions

Off Indication on GT3X+ versus other devices

The Inclinometer feature offers researchers the ability to detect periods of time during which the device was not worn.

For non-GT3X+ devices, the inclinometer algorithm makes this prediction by examining the angle at which the device is

placed. In GT3X+ devices, off detection 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.

Lux (Ambient Light)

Some devices contain an ambient light sensor capable of measuring the intensity of light. Lux data is stored once per

epoch. For GT3X+ devices, Lux data is stored once per second. When converting a GT3X+ raw file into an accumulated

*.agd format with epoch lengths greater than one second (see

Uncompressing *.gt3x Files), the lux values for that epoch

are averaged. An estimate of lux values is shown in Table 2.

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 93 94

Žádné komentáře

ActiGraph ACTITRAINER Uživatelský manuál Strana 15