CO2 measurement settings

CO2 boundary levels

Configure the boundary levels of the CO2 zones.

SET

Set the boundary levels.

Byte index	Bit index	Hex value – Meaning
0	-	1E – The command code.
1	15:8	Good-medium CO2 zone boundary value in ppm [high byte].
2	7:0	Good-medium CO2 zone boundary value in ppm [low byte]. Default value 0x0384=900ppm.
3	15:8	Medium-bad CO2 zone boundary value in ppm [high byte].
4	7:0	Medium-bad CO2 zone boundary value in ppm [low byte]. Default value 0x05DC=1500ppm.

Example command: 0x1E038405DC – set the Good-medium CO2 zone to 0x3840=900ppm and the Medium-bad CO2 zone to 0x05DC=1500ppm.

GET

CO2 auto-zero value

In practice, you are not supposed to change the auto-zero value, as this would directly affect the internal self-calibration algorithm.

You can get the CO2 auto-zero value in order to check whether normal calibration has worked correctly - e.g. expected values are in the range 0-1500ppm. If you see value of e.g. 20000, please use the SET function to set it back to 400ppm and leave the sensor at fresh air for at least 1.2xMeasurement intervals (if you are using default settings, expose the sensor to fresh air for at least 15 minutes).

This command set is used by the device for CO2 measurements compensation in order to get 400ppm in fresh air.

SET

Set the auto-zero value.

Byte index	Bit index	Hex value – Meaning
0	-	20 – The command code.
1	15:8	Auto-zero CO2 value in ppm [higher byte].
2	7:0	Auto-zero CO2 value in ppm [lower byte]. Default value 0x0190=400ppm.

Example command: 0x200221 – Set the CO2 auto-zero value to 0x0221=545ppm.

GET

CO2 measurement period

The commands configures the CO2 measurement period.

SET

Set the measurement period.

Byte index	Bit index	Hex value – Meaning
0	-	24 – The command code.
1	-	Measurement period in the Good-zone in minutes. Default value 0x0A=10min.
2	-	Measurement period in the Medium-zone in minutes. Default value 0x0A=10min.
3	-	Measurement period in the Bad-zone in minutes. Default value 0x0A=10min.

Example command: 0x240F0F0F – Set the measurement periods for all 3 zones to be the same 0x0F=15min.

GET

CO2 auto-zero period

Default auto-zero period, after the factory auto-zeroing, is 192 hours (8 days). During this period the lowest measured CO2 value is accepted as 400ppm and the auto-zero value is obtained automatically. If The period is 0, automatic auto-zero function is disabled, but the obtained or set with command auto-zero value is still used internally.

SET

Set the auto-zero period.

Byte index	Bit index	Hex value – Meaning
0	-	2A – The command code.
1	-	Auto-zero period in hours. Default value 0xC0=192hrs.

Example command: 0x2A48 – Set the CO2 auto-zero period to 0x48=72hrs.

GET