How to calibrate CO2 sensor through a downlink message

CO2 calibration can be done 3 ways:

- manual calibration with device preset settings (fresh air calibration) : use button

- manual calibration with customizable setting (X calibration), it needs a server downlink

- automatic calibration (fine tune calibration), its needs a server downlink. Thishas to be done every 10 days to prevent from sensor deviation.

We suggest to send automatic calibration DL only after Monitoring messages, sent by the device twice a day.

The calibration DL message should be sent from the server side to trigger a calibration of the CO2 sensor.

	Byte 0	Byte 1	Byte 2	Byte 3	Byte 4	Byte 5	Byte 6	Byte 7
Value	Message code	Calibration type	PPM level actually measured*	PPM level expected	Reserved	Reserved	Reserved	Reserved
Hexa	0x{41}	0x{01}	0x{46}	0x{28}	0x{00}	0x{00}	0x{00}	0x{00}
Decimal	65	1	70	40	0	0	0	0
Unit	-	-	Deca PPM	Deca PPM	-	-	-	-

 * : good strategy is to calculate the minimum level of CO2 for last 10 days and push in the downlink 400 ppm as the target

Byte 1 is dedicated to calibration type as below

Code	Type	Params
0x00	CO2 Fresh air calibration (G)	0
0x01	CO2 Fine tune calibration (F)	2 (x,y)
0x02	CO2 known gas concentration calibration (X)	1 (x)

Byte 2 : X value

Byte 3 : Y value

After calibration process, the device will send notification message with 0x11 prefix as the first byte and following code for the second byte

Code	Type
0x00	Ack CO2 Fresh air calibration (G)
0x01	Ack CO2 Fine tune calibration (F)
0x02	Ack CO2 with known gas concentration calibration (X)