16
www.xsens.com
3.3.2
Advertisement
In advertisement mode sensor will perform operation idle detection, waiting for BLE
connection from host devices. If no BLE connection is detected over 10 minutes
4
during
advertisement, sensor will enter power saving mode.
3.3.3
Connection
Once the Bluetooth connection is established, information such as MAC address, device tag
name, battery level and charging status... etc. can be retrieved from the sensor. In Xsens
DOT App, a reconnection will start automatically once the connection is lost.
If no measurement is started over 30 minutes
5
during connection, sensor will enter power
saving mode.
There is no sensor connection limit set in any software provided by Xsens. Though a max
5 sensors can be used for real-time streaming to guarantee a good performance of BLE
data transmission. Refer to section 2.4.1 for best practices on connecting multiple sensors.
3.3.4
Synchronization
Each sensor has its own clock domain. So, it is important to have the measurement data
time-synchronized between different sensors, especially in scenarios where multiple
sensors are required simultaneously, e.g., joint angles.
All the sensors will be time-synced to a common sensor time base after synchronization.
As the sensor clock drifts, the synchronization accuracy will decrease over time.
Table 5: Synchronization accuracy
Time
Accuracy
After 30 min
1 ppm
After 1 hour
4 ppm
A successful synchronization will take about 14 seconds. During the synchronization, one
sensor will be the root node, whereas the remaining sensors are scanners. The root node
will periodically send out advertisement messages while the scanners will receive the
messages and correct their own time domain by calculating the skew and offset of the root
clock.
To achieve a better synchronization result, it is advised to put the root node in a central
position of all the scanners. In Xsens DOT app, the first connected sensor will be the root
node. SDK users and other developers can set their own rules to choose the root node.
4
Default time threshold which can be changed in Xsens DOT App, SDK or by BLE services.
5
Default time threshold which can be changed in Xsens DOT App, SDK or by BLE services.
