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 of different measurement principles, Sensirion offers solutions for a wide range of use cases and requirements. From initial idea to product launch, Sensirion 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 sensor 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)
CO2 molecules absorb specific wavelengths of infrared (IR) light. NDIR CO2 sensors pass IR light through a measurement cell, using a detector to measure how much light is transmitted through it (i.e., not absorbed by CO2 molecules). By comparison to a reference light intensity, a CO2 concentration is derived. Two types of NDIR CO2 sensors exist: single and dual channel. The reference measurement channel in dual channel NDIR enhances long-term stability.
Diagram Description: An illustration shows an IR light source emitting light that passes through a gas molecule and a CO2 molecule. An IR filter and detector are positioned to measure the transmitted light, with the signal going to a PCB.
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.
Diagram Description: An illustration depicts a pulsed MEMS IR emitter emitting light that passes through a gas molecule and a CO2 molecule. An IR filter is present. An acoustic wave is generated and detected by a microphone, which sends a signal to a PCB. A protective membrane is also shown.
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.
Diagram Description: An illustration shows a heater and a temperature sensor within a measurement cavity. A protective membrane is present. The heat transfer is measured, and the signal is sent to an ASIC on a PCB.
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.
Diagram Description: An image shows the SCD30 sensor module, a small square component with pins and a metallic top surface labeled "SCD40".
Features and Benefits
| Features | Benefits |
|---|---|
| Transmissive NDIR sensing technology | High accuracy, selective optical CO2 measurement |
| Dual-channel measurement principle | Superior long-term stability by reference-channel compensation |
| All-in-one CO2, RH and T sensor module | Three measurement outputs with on-board temperature and humidity compensation |
| Sensirion CMOSens® IR-Detector | Excellent performance-to-price ratio |
| UART, I²C and PWM interface | High flexibility for interfacing and read-out |
| Thinnest NDIR sensor module | 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 and SEK-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.
Diagram Description: An image shows the SCD41 sensor module, a small square component with pins and a metallic top surface labeled "SCD41".
Features and Benefits (SCD4x)
| Features | Benefits |
|---|---|
| Photoacoustic NDIR sensing technology | High accuracy, selective CO2 measurement |
| Small footprint of 10.1 × 10.1 × 6.5 mm³ | Space saving integration |
| Fully encapsulated sensor package | Long lifetime of > 10 years |
| SMD solderable, tape & reel packaging | Robust against dust, water ingress and mechanical force |
| On-chip compensation and self-calibration | Allows for highly automated, cost-effective on-board assembly |
| Supply voltage range of 2.4-5.5 V | Calibrated and linearized sensor output with long-term drift compensation (ASC) |
| Multiple operation and reduced power modes | Operable in wide variety of applications |
| Digital I²C interface | 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, and 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.
Diagram Description: An image shows the STCC4 sensor module, a very small rectangular component with pins.
Features and Benefits
| Features | Benefits |
|---|---|
| Thermal conductivity sensing technology | Direct measurement of CO2 concentration |
| Small footprint of 4 × 3 × 1.2 mm³ | Facilitates space-efficient design-in |
| Current consumption of 950μΑ | Enables low power applications |
| Low number of components | High reliability |
| SMD soldering, tape & reel packaging | Straight-forward design-in |
| Digital I²C interface | 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 and 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.
Diagram Description: An image shows the STC31-C sensor, a small black chip with pins.
Features and Benefits
| Features | Benefits |
|---|---|
| Thermal conductivity sensing technology | Ultra-low power consumption |
| Small footprint of only 4 × 3 × 1mm³ | Fits into every device |
| Low number of components | High reliability |
| Fast response time | Allows measurement of CO2 in breath |
| Voltage range of 2.7-5.5 V | Flexibility for battery and wired applications |
| Automatic self-calibration (ASC) | Enables autonomous drift compensation |
| Low-power mode | Potential for battery-powered applications |
| SMD soldering, tape & reel packaging | Straight-forward design-in |
| Smart humidity and O2 compensation | On-chip signal compensation |
| Digital I²C interface | 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 and SEK-STC31.
Technical Specifications Comparison
| SCD30 | SCD40 | SCD41 | SCD43 | STCC4 | STC31-C | |
|---|---|---|---|---|---|---|
| Measurement principle | NDIR | Photoacoustic NDIR | Photoacoustic NDIR | Photoacoustic NDIR | Thermal conductivity | Thermal conductivity |
| Measurement accuracy | ± (30 ppm +3%) | ± (50ppm + 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 |
± (100 ppm +10%) | ± (0.2 ... 2.0 vol%) | ± (30 ppm + 3% of reading) @400-5,000 ppm |
| CO2 output range | 400-10,000ppm | 0-40,000 ppm | 0-40,000 ppm | 0-40,000 ppm | 0-100 vol% | 0-100 vol% |
| Minimum sampling interval | 2s | 5 s | 5 s | 5 s | 0.066 s | 1s |
| Response time (T63%) | 20 s | 60 s | 60 s | 60 s | 0.5 s | 20 s |
| Size | 35×23×7mm³ | 10.1×10.1×6.5 mm³ | 10.1×10.1×6.5 mm³ | 10.1×10.1×6.5 mm³ | 4×3×1.2 mm³ | 4×3×1mm³ |
| Assembly | Through-hole | SMD | SMD | SMD | SMD | SMD |
| Interface | I2C, PWM, Modbus | I2C | I2C | I2C | I2C | I2C |
| Lifetime | 15 years | > 10 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 | 2.4-5.5 V | 2.7-5.5 V | 2.7-5.5 V |
| Average current for periodic measurement mode | 19 mA | 3.3 V = 15 mA, 5V = 11 mA | 3.3 V = 15 mA, 5V = 11 mA | 3.3 V = 15 mA, 5V = 11 mA | 950μΑ @ 1 Hz | 150uA @ 1Hz |
| Temperature operating conditions | 0 to 50°C | -10 to +60 °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 | 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 |
| Compatibility with IAQ standards | EN50543, RESET, WELL, California Title 24 | WELL | RESET, WELL, California Title 24, ASHRAE 62.1-2022 incl. Draft Addendum d | RESET, WELL, California Title 24, ASHRAE 62.1-2022 incl. Draft Addendum d | Not for IAQ applications | WELL |
