High-G event detection is supported on a select group of Digital Matter devices. High-G events can be enabled in the Accelerometer Settings tab on OEM server:
|Oyster||1.6 and above|
|Remora||1.35 and above|
Because High-G detection requires the accelerometer to run at a higher speed than usual (100 Hz, versus the usual 12.5 Hz), it is disabled by default. This saves a small amount of battery:
|State||Current||Alkaline Battery / Year|
(Periodic Only tracking, High-G events disabled)
|0 uA||0 %|
|Accelerometer On @ 12.5 Hz|
(Normal tracking, High-G events disabled)
|6 uA||0.75 %|
|Accelerometer On @ 100 Hz|
(High-G events enabled)
|24 uA||3 %|
When enabled, the accelerometer will detect High-G events exceeding the specified force and duration, and log a record containing:
- Log reason 'High-G Event' (46)
- The current time
- The last known GPS time and position
- The peak force seen
- The average force seen
- The duration of the event
Since the immediate record contains only the last known GPS position, the High-G Event Action can be configured to attempt a GPS fix after each High-G event. It can also be told to attempt to upload the result of the fix once, or to continue retrying the fix/upload until they succeed, with increasing back-off timeouts in the event of failure.
In addition to requiring additional battery power for the accelerometer, High-G events use battery when responding to each event. The device must wake up whenever it sees a large force, and verify that the force meets the criteria for logging.
Because the accelerometer is sensitive to gravity, it wakes up more easily when experiencing vertical forces. However, gravity is not considered when evaluating the criteria for logging. This filters out nuisance events from speed bumps, but might in extreme circumstances allow many High-G event wake-ups to go unnoticed, as they did not lead to a logged event.
When using High-G detection in situations prone to repetitive vertical forces (for instance, on corrugated roads, or with continually vibrating machinery) be sure to set the force threshold high enough to avoid repetitive wake-ups, and the associated battery use.
The default threshold of 2Gs is suitable for regular vehicle tracking, where continuous vertical forces are not expected. To determine the minimum safe threshold in challenging environments:
- Set the High-G Event Force threshold to its minimum value (1.5 G @ 10 ms)
- Test the device in its intended application
- If the detector doesn't go off, a threshold of at least 2.6 G is safe
- If it does go off repeatedly, add at least 1.1 G to the reported peak force
High-G Event Reporting in Telematics Guru
When the device is configured to for High-G event detection, events will be reported in the Telematics Guru Telemetry in the following way:
Log Reason: High G Event (Field Type ID 24)
Values are mapped into the following Analogues by default:
Analogue 18: Peak G-Force
Analogue 19: Average G-Force
Analogue 20: Duration of the event
The Log Reason enables alerts to be set up to notify users of a High-G Event.
To report on High-G Events, simply create an Event Type (Admin -> Event Types), and link it to your alert under the Alert's Advanced tab.