On-demand measurement of relative humidity and temperature only, significantly reduces power
consumption. The sensor output is read out by using the read_measurement command. CO2 output is
returned as 0 ppm.
Configuration settings such as the temperature offset, sensor altitude and the ASC
enabled/disabled parameters are by default stored in the volatile memory (RAM) only. This
command stores the current configuration in the EEPROM of the SCD4x, ensuring the current
settings persist after power-cycling. To avoid unnecessary wear of the EEPROM, this command
should only be sent following configuration changes whose persistence is required. The EEPROM
is guaranteed to withstand at least 2000 write cycles. Note that field calibration history
(i.e. FRC and ASC) is automatically stored in a separate EEPROM dimensioned for the specified
sensor lifetime when operated continuously in either periodic measurement mode, low power
periodic measurement mode or single shot mode with 5 minute measurement interval (SCD41 and
SCD43 only).
Reads the sensor output. The measurement data can only be read out once per signal update
interval as the buffer is emptied upon read-out. If no data is available in the buffer, the
sensor returns a NACK. To avoid a NACK response, GetDataReady can be issued to check
data status. The I2C master can abort the read transfer with a NACK followed by a STOP
condition after any data byte if the user is not interested in subsequent data.
Reinitializes the sensor by reloading user settings from EEPROM. The sensor must be in the idle
state before sending the reinit command. If the reinit command does not trigger the desired
re-initialization, a power-cycle should be applied to the SCD4x.
Sets the ambient pressure value. The ambient pressure can be used for pressure
compensation in the CO2 sensor. Setting an ambient pressure overrides any pressure compensation
based on a previously set sensor altitude. Use of this command is recommended for applications
experiencing significant ambient pressure changes to ensure CO2 sensor accuracy. Valid input
values are between 700 to 1200 hPa. The default value is 1013 hPa.
Sets the status of the CO2 sensor automatic self-calibration (ASC). The CO2 sensor supports
automatic self-calibration (ASC) for long-term stability of the CO2 output. This feature can be
enabled or disabled. By default, it is enabled.
Sets the duration of the initial period for ASC correction (in hours). By default, the initial
period for ASC correction is 44 hours. Allowed values are integer multiples of 4 hours. A value
of 0 results in an immediate correction. To save the setting to the EEPROM, the
PersistSettings command must be issued.
Sets the standard period for ASC correction (in hours). By default, the standard period for ASC
correction is 156 hours. Allowed values are integer multiples of 4 hours. A value of 0 results
in an immediate correction. To save the setting to the EEPROM, the PersistSettings command
must be issued.
Sets the value of the ASC baseline target, i.e. the CO2 concentration in ppm which the ASC
algorithm will assume as lower-bound background to which the SCD4x is exposed to regularly
within one ASC period of operation. To save the setting to the EEPROM, the PersistSettings
command must be issued subsequently.
Reading and writing the sensor altitude must be done while the SCD4x is in idle mode.
Typically, the sensor altitude is set once after device installation. To save the setting to
the EEPROM, the PersistSettings command must be issued. The default sensor altitude value
is set to 0 meters above sea level. Valid input values are between 0 - 3000 m.
Setting the temperature offset of the SCD4x inside the customer device allows the user to
optimize the RH and T output signal. The temperature offset can depend on several factors such
as the SCD4x measurement mode, self-heating of close components, the ambient temperature and
air flow. Thus, the SCD4x temperature offset should be determined after integration into the
final device and under its typical operating conditions (including the operation mode to be
used in the application) in thermal equilibrium. By default, the temperature offset is set to 4
°C. To save the setting to the EEPROM, the PersistSettings command may be issued.
To enable use-cases with a constrained power budget, the SCD4x features a low power periodic
measurement mode with a signal update interval of approximately 30 seconds.
Command returns a sensor running in periodic measurement mode or low power periodic measurement
mode back to the idle state, e.g. to then allow changing the sensor configuration or to save
power.
Wake up the sensor from sleep mode into idle mode. Note that the SCD4x does not acknowledge the
wake_up command. The sensor’s idle state after wake up can be verified by reading out the
serial number.