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Version 1.1 – April 2021

12/22

3.6.5

set_ambient_pressure

Description: The set_ambient_pressure command can be sent during periodic measurements to enable continuous pressure

compensation. Note that setting an ambient pressure using set_ambient_pressure overrides any pressure compensation based

on a previously set sensor altitude.

Write

(hexadecimal)

Input parameter: Ambient pressure

Response parameter: -

Max. command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0xe000

3

word[0] = ambient P [Pa] /

100

-

-

1

Example: set ambient pressure to 98’700 Pa

Write

0xe000

0x03db

0x42

(hexadecimal)

Command

Ambient P = 98’700 Pa

CRC of 0x03db

3.7 Field Calibration

To realize high initial and long-term accuracy, the SCD4x includes two field calibration features. Forced recalibration (FRC)

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

ensures highest long-term stability of the SCD4x without the need of manual action steps from the user. The automatic self-

week.

3.7.1

perform_forced_recalibration

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

1.

Operate the SCD4x in the operation mode later used in normal sensor operation (periodic measurement, low power

concentration.

2.

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

3.

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.