Carbon dioxide sensors
Precise monitoring in any environment
Bringing value through CO2 sensing
CO2 sensors enable the development of smart devices that enhance comfort, health, and energy efficiency in a variety of HVAC, consumer, and medical applications. Utilizing the latest advancements in different measurement principles, Sensirion offers solutions for a wide range of use cases and requirements. From initial idea to product launch, the company supports the entire development process, offering expertise in prototype construction, design-in support, and in-line testing during mass production. The sensor portfolio also includes solutions to monitor environmental parameters such as humidity, temperature, volatile organic compounds (VOCs), particulate matter (PM), formaldehyde, and nitrogen oxide (NOx).
Measurement principles for CO2 sensing
Transmissive non-dispersive infrared (NDIR)
This principle involves a light source emitting infrared (IR) light. CO2 molecules absorb specific wavelengths of this IR light as it passes through a measurement cell. A detector measures the amount of light transmitted. By comparing the transmitted light to a reference intensity, the CO2 concentration is determined. Two types of NDIR CO2 sensors exist: single and dual channel. The reference measurement channel in dual channel NDIR enhances long-term stability.
Photoacoustic NDIR (PA)
PA uses a pulsed IR light source that emits wavelengths absorbed by CO2. Absorption of light by CO2 molecules leads to additional molecular vibration, increasing the pressure in the measurement cell. As the light source is pulsed, this pressure increase occurs periodically, creating an acoustic wave. The more CO2 molecules present, the larger the amplitude of the acoustic wave. This is measured by a microphone to calculate the CO2 concentration.
Thermal conductivity (TC)
TC is based on the inherent thermal conductivity of all gases. With a thorough understanding of the gas composition in ambient environments, subtle changes in gas concentrations can be detected. The measurement principle is based on heating the air within a measurement cavity and sensing the heat transfer with a temperature sensor.
SCD30
SCD30 is Sensirion's state-of-the-art transmissive NDIR CO2, relative humidity, and temperature sensor module. The module's dual-channel optical measurement principle enables best-in-class CO2 measurement accuracy and excellent long-term stability. An ultra-thin package size and UART, I²C, or PWM interface allows for easy, space-saving integration. Applications requiring compatibility with building codes or IAQ standards – such as California Title 24, EN50543, RESET®, or WELL Building Standard® – are well served by SCD30.
Features
- Transmissive NDIR sensing technology
- Dual-channel measurement principle
- All-in-one CO2, RH, and T sensor module
- Sensirion CMOSens® IR-Detector
- UART, I²C, and PWM interface
- Thinnest NDIR sensor module
Benefits
- High accuracy, selective optical CO2 measurement
- Superior long-term stability by reference-channel compensation
- Three measurement outputs with on-board temperature and humidity compensation
- Excellent performance-to-price ratio
- High flexibility for interfacing and read-out
- Streamlined design, ideal for wall-mounted devices
Applications
- Commercial and residential HVAC systems
- Demand-controlled ventilation (DCV)
- Energy recovery ventilation (ERV)
- Wall-mounted thermostats
- Duct-mounted CO2 sensors
SEK-SCD30 Evaluation Kit
- 1x SCD30 on SEK-adapter PCB with RJ45 connector and pinout (female 2.54 mm)
- 1x RJ45 adapter cable (1-meter length)
- 1 × SEK-SensorBridge required (must be bought separately)
Learn more about the SCD30
SCD4x
SCD4x offers high accuracy at attractive prices and a small form factor using the photoacoustic NDIR sensing principle and Sensirion's patented PASens® and CMOSens® technologies. SCD4x is available in three different variants: SCD40 for cost-sensitive applications at standard accuracy, SCD41 for more demanding use-cases requiring compatibility with California Title 24, RESET®, and WELL Building Standard™, and SCD43 for applications additionally requiring compatibility with ASHRAE 62.1-2022 Draft Addendum d and/or high accuracy. SCD41 and SCD43 also feature a single shot operation mode.
Features
- Photoacoustic NDIR sensing technology
- Small footprint of 10.1 × 10.1 × 6.5 mm³
- Fully encapsulated sensor package
- SMD solderable, tape & reel packaging
- On-chip compensation and self-calibration
- Supply voltage range of 2.4–5.5 V
- Multiple operation and reduced power modes
- Digital I²C interface
Benefits
- High accuracy, selective CO2 measurement
- Space saving integration
- Long lifetime of > 10 years
- Robust against dust, water ingress, and mechanical force
- Allows for highly automated, cost-effective on-board assembly
- Calibrated and linearized sensor output with long-term drift compensation (ASC)
- Operable in a wide variety of applications
- Flexible trade-off between power-consumption and performance
- Straight-forward design-in and interfacing
Applications
- Commercial or residential HVAC systems
- Wall-mounted thermostats
- Air purifiers
- Indoor air quality monitors
SEK-SCD41 Evaluation Kit
- 1× SCD41 development board
- 1x adapter cable
- 1x jumper wire set
- 1× SEK-SensorBridge required (must be bought separately)
Learn more about the SCD40, SCD41, SEK-SCD41, SCD43
STCC4
STCC4 is Sensirion's next-generation CO2 sensor based on the thermal conductivity sensing principle. With one of the world's smallest form factors on the market for direct measurement of CO2 gas concentrations, it is designed for seamless integration into compact electronic devices, setting a new standard for versatility and adaptability. The key features of STCC4 open up opportunities for CO2 monitoring in applications previously limited by size and cost constraints. The sensor will officially be launched in May 2025.
Features
- Thermal conductivity sensing technology
- Small footprint of 4 × 3 × 1.2 mm³
- Current consumption of 950µA
- Low number of components
- SMD soldering, tape & reel packaging
- Digital I²C interface
Benefits
- Direct measurement of CO2 concentration
- Facilitates space-efficient design-in
- Enables low power applications
- High reliability
- Straight-forward design-in
- Simple sensor communication
Applications
- Smart speakers
- Smart thermostats
- Air conditioners
- Indoor air quality monitors
SEK-STCC4 Evaluation Kit
- 1x STCC4 development board
- 1x adapter cable
- 1x jumper wire set
- 1× SEK-SensorBridge required (must be bought separately)
Learn more about the STCC4, SEK-STCC4
STC31-C
STC31-C is a chip-sized gas concentration sensor based on the thermal conductivity sensing principle that delivers high-range, accurate CO2 measurements with superior repeatability and long-term stability. This makes it the perfect choice for applications where reliability is key. STC31-C introduces a new low-cross-sensitivity measurement mode with smart humidity and oxygen compensation, allowing new applications like measuring CO2 in breath.
Features
- Thermal conductivity sensing technology
- Small footprint of only 4 × 3 × 1mm³
- Low number of components
- Fast response time
- Voltage range of 2.7–5.5 V
- Automatic self-calibration (ASC)
- Low-power mode
- SMD soldering, tape & reel packaging
- Smart humidity and O2 compensation
- Digital I²C interface
Benefits
- Ultra-low power consumption
- Fits into every device
- High reliability
- Allows measurement of CO2 in breath
- Flexibility for battery and wired applications
- Enables autonomous drift compensation
- Potential for battery-powered applications
- Straight-forward design-in
- On-chip signal compensation
- Simple sensor communication
Applications
- Controlled atmosphere storage systems
- CO2 measurement in breath
- CO2 measurement in medical ventilation
- CO2 leakage detection
SEK-STC31-C Evaluation Kit
- 1× STC31-C and 1 × SHT40 on FPCB
- 1x RJ45 adapter cable (1 meter length)
- 1× SEK-SensorBridge required (must be bought separately)
Learn more about the STC31-C, SEK-STC31
Product Comparison
| Feature | SCD30 | SCD40 | SCD41 | SCD43 | STCC4 | STC31-C |
|---|---|---|---|---|---|---|
| Measurement principle | NDIR | NDIR | Photoacoustic NDIR | Photoacoustic NDIR | Thermal conductivity | Thermal conductivity |
| Measurement accuracy | ± (30 ppm +3%) | ± (50 ppm +5% of reading) @ 400-2,000 ppm | ± (50 ppm + 2.5% of reading) @ 400-1,000 ppm ± (50 ppm +3% of reading) @ 1,001-2,000 ppm ± (40 ppm + 5% of reading) @ 2,001-5,000 ppm | ± (30 ppm +3% of reading) @ 400-5,000 ppm | ± (100 ppm + 10%) | ± (0.2 ... 2.0 vol%) |
| CO2 output range | 400-10,000ppm | 0-40,000 ppm | 0-40,000 ppm | 400-5,000 ppm | 0-100 vol% | |
| Minimum sampling interval | 2s | 5s | 5s | 1s | 0.066 s | |
| Response time (T63%) | 20 s | 60 s | 60 s | 20 s | 0.5 s | |
| Size | 35×23×7 mm³ | 10.1×10.1× 6.5 mm³ | 10.1×10.1× 6.5 mm³ | 4×3×1.2 mm³ | 4×3×1 mm³ | |
| Assembly | Through-hole | SMD | SMD | SMD | SMD | |
| Interface | I²C, PWM, Modbus | I²C | I²C | I²C | I²C | |
| Lifetime | 15 years | > 10 years | > 10 years | > 10 years | > 10 years | |
| Supply voltage range | 3.3-5.5 V | 2.4-5.5 V | 2.4-5.5 V | 2.7-5.5 V | 2.7-5.5 V | |
| Average current for periodic measurement mode | 19 mA | 3.3V = 15 mA, 5V = 11 mA | 3.3V = 15 mA, 5V = 11 mA | 950µA @ 1 Hz | 150 uA @ 1Hz | |
| Temperature operating conditions | 0 to 50°C | -10 to +60°C | -10 to +60°C | 10 to 40°C | -10 to +50°C | |
| Humidity operating conditions | 0-95% RH | 0-95% RH | 0-95% RH | 20-80% RH | 0-95% RH | |
| Low power modes | Variable sampling interval | Low power periodic | Low power periodic, Single shot | Low power periodic, Single shot | Single shot | Variable sampling interval |
| Compatibility with IAQ standards | EN50543, RESET, WELL, California Title 24 | WELL | RESET, WELL, California Title 24 | RESET, WELL, California Title 24, ASHRAE 62.1-2022 incl. Draft Addendum d | Single shot | Not for IAQ applications |
