SCD42-D-R2 datasheet(13/21 Pages) SENSIRION

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3.7 Field Calibration

To realize high initial and long-term accuracy, the SCD42 includes two field calibration features. Forced recalibration (FRC)

enables restoring highest accuracy with the assistance of a CO2 reference value immediately. Typically, FRC is applied to

compensate for drifts originating from the sensor assembly process or other extensive stresses. Automatic self-calibration (ASC)

ensures highest long-term stability of the SCD42 without the need of manual action steps from the user. The automatic self-

calibration algorithm assumes that the sensor is exposed to the atmospheric CO2 concentration of 400 ppm at least once per

week.

3.7.1

perform_forced_recalibration

Description: To successfully conduct an accurate forced recalibration, the following steps need to be carried out:

Operate the SCD42 in the operation mode later used in normal sensor operation for > 3 minutes in an environment

with homogenous and constant CO2 concentration.

Issue stop_periodic_measurement. Wait 500 ms for the stop command to complete.

Subsequently issue the perform_forced_recalibration command and optionally read out the FRC correction (i.e. the

magnitude of the correction) after waiting for 400 ms for the command to complete.

• A return value of 0xffff indicates that the forced recalibration has failed.

Note that the sensor will fail to perform a forced recalibration if it was not operated before sending the command. Please make

sure that the sensor is operated at the voltage desired for the application when applying the forced recalibration sequence.

Table 18: perform_forced_recalibration I2C sequence description

Write

(hexadecimal)

Input parameter: Target CO2 concentration

Response parameter: FRC-correction

Max.

command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0x362f

word[0] = Target

concentration [ppm CO2]

FRC correction [ppm CO2] =

word[0] – 0x8000

word[0] = 0xffff in case of

failed FRC

400

Example: perform forced recalibration, reference CO2 concentration is 480 ppm

Write

0x362f

0x01e0

0xb4

(hexadecimal)

Command

Input: 480 ppm

CRC of 0x01e0

Wait

400 ms

command execution time

Response

0x7fce

0x7b

(hexadecimal)

Response: - 50 ppm

CRC of 0x7fce

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