Low Power Mode for SCD30
CO2, humidity, and temperature sensor
Preface
The SCD30 sensor module is an optical NDIR sensor thatmeasures the CO2 concentration at regular time intervals.
By default, the interval between two measurements is 2seconds. The SCD30 features the possibility to customize
the sampling interval, which can reduce power
consumption by more than a factor of three. To ensure
accuracy of the CO2, temperature and relative humidity

output signals, subsequent sensor recalibration isnecessary. This document provides detailed instructionson how to adjust the CO2-sampling interval and how tosubsequently recalibrate the sensor output signals.
Furthermore, the impact of the sampling interval on theresponse time, power consumption, and the signal
accuracy are discussed.

Overview

Finding a suitable sampling interval

The SCD30 sensor module features a low power mode that
reduces power consumption by more than a factor of threecompared to normal mode of operation. This document
provides instructions on how to initiate the low power mode,
and includes an overview of relevant technical aspects ofthe SCD30. Figure 1 depicts an overview over the process
steps required to operate the SCD30 sensor module in low
power mode.

As a first process step, the user must decide on a suitablesampling interval. The sampling interval can be set to any
integer value between 1 second and 1800 seconds.
However, there is an inherent trade-off between low power
consumption and fast response time. This is schematically
depicted in figure 2: while the power consumption isminimized at high sampling intervals (red curve), theresponse time is minimized at low sampling intervals (bluecurve). Sensirion recommends to apply a sampling intervalof 5 seconds - 60 seconds to reduce power consumption
while keeping the response time low (green region infigure 2). E.g., when operated at a sampling interval of 15
seconds, the SCD30 average current consumption is 6.5mA at a response time of 72 seconds.

First, a suitable sampling interval for the CO2
measurements must be determined (i.e. the time between
two CO2 concentration measurements). Second, thesampling interval of the sensor must be set via the digitalinterface. Third, a recalibration of the CO2 output signal isnecessary. Finally, the temperature offset must bemeasured and compensated via the digital interface. The
first four chapters are dedicated to instructions on how to
implement the required process steps. Afterwards, anexample of how to initiate the low power mode is provided.
Finally, some background knowledge on the SCD30 power
consumption and response time is provided.

Figure 1: Schematic overview over the process steps that arerequired to put the SCD30 sensor module into the low powermode.

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Figure 2: Average current consumption of the SCD30 sensor
module as a function of the sampling interval (red, left y-axis). The
blue line (right y-axis) represents the response time (τ63) versus
the sampling intervals. Both curves are extrapolated fromempirical data points. The green region represents the samplinginterval range that Sensirion recommends for SCD30 low power
operation.

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Set sampling interval
The sampling interval is set via the digital interface (I2C orModbus protocol)do NOT cycle power to the sensor). The
SCD30 interface description provides detailed instructions
on how to communicate with the sensor module1.
Furthermore, an example on how to set the samplinginterval to 30 seconds is provided in the chapter “Example:
Set SCD30 to low power mode”.

temperature. Furthermore, the application device should beoperated continuously to account for external heating of theSCD30. After the new sampling interval has been set, theuser should wait approximately 10 minutes to allow thermalstabilization. Subsequently, the SCD30 offset temperature
is obtained by subtracting the reference temperature fromthe SCD30 output temperature. If the temperature offset
has been set previously, the new temperature offset can becalculated as follows:
𝑁𝑒𝑤𝑂𝑙𝑑𝑇𝑂𝑓𝑓𝑠𝑒𝑡= (𝑇𝑆𝐶𝐷30 − 𝑇𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 ) + 𝑇𝑂𝑓𝑓𝑠𝑒𝑡

Recalibration CO2 output signalModifying the SCD30 sampling interval reduces theaccuracy of the CO2 signal that can result in out-of-spec
outputs. Therefore, a subsequent CO2 signal recalibrationis necessary. After recalibration, the CO2 output is within thespecified accuracy limits for all sampling intervals.
There are two different ways to perform a SCD30 CO2
signal recalibration: Automatic Self-Calibration (ASC) andForced Recalibration (FRC). Advantages, disadvantages,
and instructions are discussed in a separate document2.
Before performing a forced recalibration, the SCD30 shouldbe operated at the newly set sampling rate for at least 6
minutes or 5 times the sampling interval (for samplingintervals larger than 72 seconds) The implementation of therecalibration is done via the digital interface and isdescribed in the SCD30 interface description1.
Furthermore, an example of a Forced Recalibration isdescribed in the chapter “Example: Set SCD30 to low powermode”. It is noteworthy, that the SCD30 will recalibrate byitself after approximately 1 – 3 weeks, if the ASC is activatedand the environment fulfills the requirements for successful
ASC operation.

𝑁𝐸𝑊𝑂𝑙𝑑Where 𝑇𝑂𝑓𝑓𝑠𝑒𝑡
corresponds to the new and 𝑇𝑂𝑓𝑓𝑠𝑒𝑡
corresponds to the old temperature offset.

After the temperature offset has been determined, it must
be set to the corrected value via the digital interface. A
detailed description of the relevant commands is provided
in the SCD30 interface description1. Additionally, anexplanatory description of setting the offset temperature isprovided in the chapter “Example: Set SCD30 to low powermode”.

Set temperature offset
Self-heating of the SCD30 sensor module results in atemperature offset that shifts the temperature and therelative humidity output signals. The temperature offset
mainly depends on two factors: the SCD30
encapsulation/environment and the power consumption ofthe sensor module. Therefore, the temperature offset isaffected by changes of the sampling interval.
The SCD30 temperature offset is defined as the difference
between the output temperature and the actual ambienttemperature. The actual ambient temperature should bemeasured with a separate calibrated reference temperature
sensor that is not in contact with any heat source. The
SCD30 must be operated in the desired application at thecorrect sampling interval to determine the offset

1 www.sensirion.com/file/scd30_interface_descriptionwww.sensirion.com

2 Field Calibration application note. Please contact yourSensirion representative for document access.
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Example: Set SCD30 to low power mode
In this chapter we provide examples for the four process
steps that are required to set the SCD30 sensor to the lowpower mode. Commands that are required for sensor
communication via the digital interface are listed for I2C andModbus protocol. Table 1 lists the parameters that are used
for the working example. It is important to realize that mostof the parameters are application and environment specific.

Parameter

Value

Sampling Interval*

30 seconds

CO2 concentration duringforced recalibration**

408 ppmTemperature offset**

2.0 °C

Table 1: List of parameters that are used for the working
example in this chapter.
* Parameter can be defined by user** Parameter must be determined/measured by user

Step 1: Determine suitable sampling interval
In this example we will implement a sampling interval of 30 seconds. This sampling interval results in an average current ofapproximately 5.6 mA and a response time of 135 seconds.
Step 2: Set sampling interval
The sampling interval can be set via I2C or Modbus protocol via the following commands:
ProtocolData to write
Start

Write
Header

Cmd
MSB

Cmd
LSB

Interval
MSB

Interval
LSB

CRC

Stop

Start

0xC2

0x46

0x00

0x00

0x1E

0x81

Stop

Slave
Address

Function
CodeAddress
MSB

Address
LSB

Content
MSB

Content
LSB

CRC
LSB

CRC
MSB

0x61

0x06

0x00

0x25

0x00

0x1E

0x11

0xA9

I2C

ModbusStep 3: Recalibration of the CO2 output signal via forced recalibration
In this example, recalibration of the CO2 output signal is done via forced recalibration (FRC). In order to perform a forced
recalibration, the CO2 concentration around the SCD30 must be stable and determined accurately. In this example the FRC is
performed at the CO2 concentration that corresponds to the atmospheric background level (408 ppm). Below, the corresponding
I2C and Modbus commands are listed:
ProtocolData to write
Start

Write
Header

Cmd
MSB

Cmd
LSB

FRC
MSB

FRC
LSB

CRC

Stop

Start

0xC20x52

0x04

0x01

0x98

0xF5

Stop

Slave
Address

Function
Code

Address
MSB

Address
LSB

Content
MSB

Content
LSB

CRC
LSB

CRC
MSB

0x61

0x06

0x00

0x39

0x01

0x98

0x50

0x5D

I2C

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Step 4: Set temperature offset
First, the temperature offset of the SCD30 must be determined. To measure the temperature offset with high precision,
the SCD30 must be operated inside its final application and with the final sampling interval. In the example below, atemperature offset of 2 °C is implemented:Protocol

Data to write

Start

Write
Header

Cmd
MSB

Cmd
LSB

SHT
OffsetMSB

SHTOffset
LSB

CRC

Stop

Start

0xC20x54

0x03

0x00

0xC80x7F

Stop

Slave
Address

Function
CodeAddress
MSB

Address
LSBContentMSB

ContentLSB

CRC
LSB

CRC
MSB

0x61

0x06

0x00

0x3B

0x00

0xC80xF0

0x31

I2CModbus

Appendix A: Effect of the sampling interval on the SCD30 response time
The response time of the SCD30 CO2 output signal is affected significantly by the sampling interval as discussed in chapter“Finding a suitable sampling interval”. Figure 5 depicts the CO2 output signal for different sampling intervals after a sudden
increase of the CO2 concentration.

Figure 5: CO2 output signal evolution of SCD30 sensor with different sampling intervals (SI) after a rapid change of the CO 2 concentration.
The red line indicates the τ63 threshold and the dotted black line indicates the CO2 concentration set point. While the response time is verylow (< 40 sec.) for small sampling intervals (2 sec and 5 sec), the response time for high sampling intervals (> 60 sec) takes several minutes.

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Revision History
DateFebruary 2019

Version0.1Page(s)allChanges
Initial version

Copyright © 2018 by SENSIRION
CMOSens® is a trademark of Sensirion
All rights reserved

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