Teknik Rehber

SCD30 vs SCD40: Which CO₂ Sensor Should You Choose?

· Fark Tedarik
Sensirion SCD30 CO2 sensor module

SCD30 and SCD40 are CO₂ sensors from Sensirion. Both also measure ambient humidity and temperature, but they differ in measurement method, size, measurement range and interface. In this article we compare the values given in the manufacturer documents for the two sensors and summarise which one is more suitable in which case. The values we use are taken from Sensirion datasheets and product pages. We explained why CO₂ measurement matters in our article What Is a CO₂ Sensor?

What is the difference in short?

SCD30 is a module based on the dual-channel NDIR principle. It offers an accuracy of ±(30 ppm + 3% of the measured value) in the 400 – 10,000 ppm range and provides I²C, UART (Modbus) and PWM outputs. SCD40, on the other hand, is a small SMD sensor soldered onto the board that works on the photoacoustic NDIR (PASens®) principle. It offers an accuracy of ±(50 ppm + 5% of the measured value) in the 400 – 2,000 ppm range and communicates only via I²C.

Key values

FeatureSCD30SCD40
Measurement principleDual-channel NDIRPhotoacoustic NDIR (PASens®)
Size35 × 23 × 7 mm, module10.1 × 10.1 × 6.5 mm, SMD (reflow solderable)
Specified measurement range400 – 10,000 ppm400 – 2,000 ppm
CO₂ accuracy±(30 ppm + 3%)±(50 ppm + 5%)
Output range0 – 40,000 ppm via I²C and UART, 0 – 5,000 ppm via PWM0 – 40,000 ppm
Response time (τ63%)20 s60 s
InterfaceI²C, UART (Modbus), PWMI²C
Supply voltage3.3 – 5.5 V2.4 – 5.5 V
Average current19 mA (one measurement every 2 seconds)15 mA
Peak current75 mA205 mA
Operating temperature0 – 50 °C-10 – 60 °C
Typical humidity accuracy±3% RH±6% RH
Source: Sensirion SCD30 and SCD4x datasheets, SCD30 and SCD40 product pages

When to choose SCD30?

  • If the CO₂ values to be measured can exceed 2,000 ppm. The specified measurement range of SCD30 goes up to 10,000 ppm.
  • If a narrower accuracy band is required. The documents give ±(30 ppm + 3%) for SCD30 and ±(50 ppm + 5%) for SCD40.
  • If the sensor will not be soldered onto the board but connected as a separate module, or if a Modbus or PWM output is needed.
  • If more accurate humidity measurement is also required. Typical humidity accuracy is ±3% RH for SCD30 and ±6% RH for SCD40.

When to choose SCD40?

  • If space in the device is limited. SCD40 fits in an area of about 10 × 10 mm.
  • If the sensor will be soldered onto the board together with the other parts in series production. Sensirion states that SCD4x is reflow solderable and supplied in tape and reel packaging.
  • If the application is indoor air quality monitoring and the 400 – 2,000 ppm range is sufficient. Sensirion states that SCD40 is compliant with the WELL Building Standard™.
  • If a wider range is needed but the SCD4x package is also wanted, the SCD41 from the same family can be considered. Sensirion specifies a 400 – 5,000 ppm measurement range and a single-shot measurement mode for SCD41.

Design considerations

The peak current of SCD40 is given as 205 mA. The supply line should be designed to handle this momentary current. Both sensors offer automatic self-calibration (ASC) and forced recalibration (FRC) options. For detailed usage we recommend referring to the relevant datasheets and Sensirion’s design guides.

Models at Fark Tedarik

For all CO₂ products see the Carbon Dioxide Sensors category. For the current price and delivery time of SCD40 you can ask through the quote form on the product page. For bulk purchases and project-based needs you can contact us.

Sources