SCD40-D-R2 datasheet(10/22 Pages) SENSIRION

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3.5.3

stop_periodic_measurement

Description: stop periodic measurement to change the sensor configuration or to save power. Note that the sensor will only

respond to other commands after waiting 500 ms after issuing the stop_periodic_measurement command.

Table 12: stop_periodic_measurement I2C sequence description

Write

(hexadecimal)

Input parameter: -

Response parameter: -

Max. command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0x3f86

500

Example: stop periodic measurement

Write

0x3f86

(hexadecimal)

Command

3.6 On-Chip Output Signal Compensation

The SCD4x features on-chip signal compensation to counteract pressure and temperature effects. Feeding the SCD4x with the

pressure or altitude enables highest accuracy of the CO2 output signal across a large pressure range. Setting the temperature

offset improves the accuracy of the relative humidity and temperature output signal. Note that the temperature offset does not

impact the accuracy of the CO2 output.

To change or read sensor settings, the SCD4x must be in idle mode. A typical sequence between the I2C master and the SCD4x

is described as follows:

If the sensor is operated in a periodic measurement mode, the I2C master sends a stop_periodic_measurement

command.

The I2C master sends one or several commands to get or set the sensor settings.

If configurations shall be preserved after power-cycle events, the persist_settings command must be sent (see

chapter 3.9.1)

The I2C master sends a start measurement command to set the sensor in the operating mode again.

3.6.1

et_temperature_offset

Description: The temperature offset has no influence on the SCD4x CO2 accuracy. Setting the temperature offset of the SCD4x

inside the customer device correctly allows the user to leverage the RH and T output signal. Note that the temperature offset

can depend on various 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 inside the customer device under its typical

operation conditions (including the operation mode to be used in the application) and in thermal equilibrium. Per default, the

temperature offset is set to 4° C. To save the setting to the EEPROM, the persist setting (see chapter 3.9.1) command must be

issued. Equation (1) shows how the characteristic temperature offset can be obtained.

��_�� = ��40 − �� + ��_ ��

(1)

Table 13: set_temperature_offset I2C sequence description

Write

(hexadecimal)

Input parameter: Offset temperature

Response parameter: -

Max. command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0x241d

word[0] = Toffset [°C] * 216 / 175

Example: set temperature offset to 5.4 °C

Write

0x241d

0x07e6

0x48

(hexadecimal)

Command

Toffset = 5.4 °C

CRC of 0x7e6

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