SENSIRION SCD4 Series, Manual, Page: 17 / 24

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3.10 Low power single shot (SCD41)
In addition to periodic measurement modes, the SCD41 features a single shot measurement mode, i.e. allows for on-demand
measurements.
The typical communication sequence is as follows:
1.
The sensor is powered up.
2.
The I
2
C master sends a single shot command and waits for the indicated max. command duration time.
3.
The I
2
C master reads out data with the read measurement sequence (chapter 3.5.2).
4.
Steps 2-3 are repeated as required by the application.
To reduce noise levels, the I
2
C master can perform several single shot measurements in a row and average the CO
2
output
values. After a power cycle, the initial single shot reading should be discarded to maximize accuracy. The idle current in between
measurements is 0.15 mA (typ.), respectively 0.2 mA (max.). The energy consumed per single shot typically is 243 mJ (296 mJ
max.).
As for the periodic measurement modes, the automatic self-calibration (ASC) is enabled per default in single shot operation.
The automatic self-calibration is optimized for single shot measurements performed every 5 minutes. Longer measurement
intervals will result in less frequent self-calibration sequences. Note that no self-calibration is issued if the sensor is power-cycled
between single shot measurements. Please consult Chapter 3.7 for a detailed description of the automatic-self calibration and
the corresponding commands.
3.10.1 measure_single_shot
Description : On-demand measurement of CO
2
concentration, relative humidity and temperature. The sensor output is read
using the read_measurement command (chapter 3.5.2).
Table 28 : measure_single_shot
I
2
C
sequence description
Write
(hexadecimal)
Input parameter: - Response parameter: -
Max. command
duration [ms]
length [bytes] signal conversion length [bytes] signal conversion
0x219d - - - - 5000
Example: measure single shot
Write 0x219d
(hexadecimal) Command
3.10.2 measure_single_shot_rht_only
Description : On-demand measurement of relative humidity and temperature only. The sensor output is read using the
read_measurement command (chapter 3.5.2). CO
2
output is returned as 0 ppm.
Table 29 : measure_single_shot_rht_only
I
2
C
sequence description
Write
(hexadecimal)
Input parameter: - Response parameter: -
Max. command
duration [ms]
length [bytes] signal conversion length [bytes] signal conversion
0x2196 - - - - 50
Example: measure single shot, RH and T output only
Write 0x2196
(hexadecimal) Command