View source for Template:FMX Ver4 Accelerometer Calibration

==Accelerometer Calibration==

Calibration algorithm is used to recalculate accelerometer axes to represent vehicle‘s axes (see Picture below). Vehicles axes are as follows:<br>
1.	X is front.<br>
2.	Y is left.<br>
3.	Z is down.<br>

[[File:Vehicle axis.PNG.png|center|800px|Vehicle Axis]]

Once vehicle‘s axes are calculated, device is considered calibrated.<br>
<br>
'''Note:''' moving forward along any axis will generate negative values. This means acceleration will generate -X values, accordingly breaking will generate X values. Same goes for other axes. <br>

Configurable parameters can be found at [[{{{model|FMB1YX}}}_System_settings#Accelerometer_Auto_Calibration|System Settings Accelerometer Auto Calibration]]

Commands that can be used during calibration:<br>
<table class="nd-othertables_2" style="width:70%; border-collapse: collapse;">
<tr>
<th style="width:1%; vertical-align: middle; text-align: center;">Command</th>
<th style="width:2%; vertical-align: middle; text-align: center;">Response</th>
<th style="width:5%; vertical-align: middle; text-align: center;">Description</th>
</tr>
<tr>
<td style="vertical-align: middle; text-align: center;">auto_calibrate:set</td>
<td style="vertical-align: middle; text-align: center;">Yes</td>
<td style="vertical-align: middle; text-align: center;">Request auto calibration task start </td>
</tr>
<tr>
<td style="vertical-align: middle; text-align: center;">auto_calibrate:get</td>
<td style="vertical-align: middle; text-align: center;">Yes</td>
<td style="vertical-align: middle; text-align: center;">Request calibration info (time, ground vector, side vector) </td>
</tr>
<tr>
<td style="vertical-align: middle; text-align: center;">auto_calibrate:clear</td>
<td style="vertical-align: middle; text-align: center;">Yes</td>
<td style="vertical-align: middle; text-align: center;">Request calibration clear from flash and stop calibration task </td>
</tr>
<tr>
<td style="vertical-align: middle; text-align: center;">auto_calibrate:status</td>
<td style="vertical-align: middle; text-align: center;">Yes</td>
<td style="vertical-align: middle; text-align: center;">Request calibration status and calibration task status </td>
</tr>

</table>

======Auto-calibration======

Auto calibration task is launched on one of these conditions (assume calibration is enabled in configuration):<br>
1.	Every time device turns on, it checks whether it was previously calibrated and has calibration stored in flash. If device has no calibration in flash, auto calibration task is started.<br>
2.	Device calibration was previously disabled by configuration and now is enabled.<br>
3.	SMS “auto_calibrate:set” is received. Note: SMS response is sent after calibration has been acquired.<br>
This SMS triggers an SMS response to be sent. Response is sent when calibration is acquired. When 1 hour passes without successful calibration, failed SMS response is sent.<br>
4.	Calibrated device’s mean axes of set interval  differ more than set amount from desired (0,0,1) calibration is considered inaccurate. Calibration is deleted from flash and auto calibration task started.<br>
After auto calibration task has been started, it will go on indefinitely until satisfactory calibration is acquired.<br>

=====Data Required=====

Auto calibration needs to fill two buffers to calibrate the device:<br>
1.	All accelerometer data – buffer which collects all data from accelerometer at 10Hz frequency. To fill this buffer set seconds of data samples are needed. When buffer is full, oldest data is dumped and new data is placed into the buffer.<br>
2.	Straight accelerometer data – buffer which collects straight accelerations data from accelerometer at 10Hz frequency. To fill this buffer set seconds  of data samples (set times Hz samples) are needed. When buffer is full, oldest data is dumped and new data is placed into the buffer. Algorithm rules to acquire these samples:<br>
2.1.	GPS fix is present.<br>
2.2.	Ignition is on.<br>
2.3.	GPS speed is more than 5 km/h.<br>
2.4.	GPS heading is equal to last GPS heading (+/-1 degree) at GPS sample rate 1Hz.<br>
2.5.	GPS speed more then 5 km/h from last sample (accelerating).<br>
Once both buffers are full, auto calibration is attempted. If calibrated values pass calibration quality threshold, calculated calibration is written to flash as current calibration – device is calibrated. <br>
Note: If GPS fix is lost or ignition is turned off, buffers’ data is dumped and must be gathered from 0 again.<br>

At this point calibration is successfully ended as indication device sends an SMS/GPRS message with ''Device is calibrated, to recalibrate send:auto_calibrate:set.<br>''

''Note: SMS/GPRS message will be sent only if auto calibration functionality was triggered by SMS/GPRS message.''
For user convenience in case auto calibration functionality fails then notification message will be sent. For exact messages, check algorithm section.<br>
''Note: SMS/GPRS message will be sent only if auto calibration functionality was triggered by SMS/GPRS message.''
To get current calibration status ''auto_calibrate:get'' SMS/GPRS command must be sent to the device. If device is calibrated it will respond with ''Calibration state: calibrated'' or otherwise ''Calibration state: not calibrated''. Also this command returns saved Ground and Side vectors.<br>


=====Re-Calibration=====

When calibration is present, device checks for re-calibration every 60s indefinitely. Re-calibration requires fix and ignition to run also re-calibration is turned off when vehicle is stopped for more than 15s until conditions are satisfied again. When calibrated device’s mean axes of set interval(calibrated accelerometer data) differ more than set amount from desired (0,0,1) (perfect vehicle’s axes) calibration is considered inaccurate, or device’s position has changed and re-calibration is needed. Calibration is cleared from flash and auto calibration task is started.<br/>
Note: turning device around calibrated Z axis will not trigger re-calibration, after turning device around Z axis manual re-calibration is advised. After calibration if quality value is less than 0.80, calibration update functionality is run. Calibration update constantly tries calibrating device in background until 0.80 quality is reached. Calibration update functionality does not change calibration if calculated new calibration quality is less than 0.80.<br/>