SENSIRION SCD4 Series, Manual, Page: 10 / 24

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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 I
2
C 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 CO
2
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 CO
2
output.
To change or read sensor settings, the SCD4x must be in idle mode. A typical sequence between the I
2
C master and the SCD4x
is described as follows:
1.
If the sensor is operated in a periodic measurement mode, the I
2
C master sends a stop_periodic_measurement
command.
2.
The I
2
C master sends one or several commands to get or set the sensor settings.
3.
If configurations shall be preserved after power-cycle events, the persist_settings command must be sent (see
chapter 3.9.1)
4.
The I
2
C master sends a start measurement command to set the sensor in the operating mode again.
3.6.1
s
et_temperature_offset
Description : The temperature offset has no influence on the SCD4x CO
2
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.
𝑇
𝑜𝑓𝑓𝑠𝑒𝑡_𝑎𝑐𝑡𝑢𝑎𝑙
= 𝑇
𝑆𝐶𝐷40
− 𝑇
𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
+ 𝑇
𝑜𝑓𝑓𝑠𝑒𝑡_ 𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠
(1)
Table 13 : set_temperature_offset I
2
C sequence description
Write
(hexadecimal)
Input parameter: Offset temperature Response parameter: -
Max. command
duration [ms]
length [bytes] signal conversion length [bytes] signal conversion
0x241d 3 word[0] = T
offset
[°C] * 2
16
/ 175 - - 1
Example: set temperature offset to 5.4 °C
Write 0x241d 0x07e6 0x48
(hexadecimal) Command T
offset
= 5.4 °C CRC of 0x7e6