Deploy Miniature Sensirion CO2 Sensors for Accurate Indoor Air Quality Monitoring

CO₂ sensors by Sensirion: Thermal conductivity-based measurement

Sensirion's STC31-C and STCC4 sensors measure thermal conductivity and use it to determine gas concentration. Being non-selective, the sensors cannot differentiate which specific gas caused the change in thermal conductivity, but the measurement method allows for effective use in indoor and controlled atmospheres where the gas composition is known.

Environmental properties

• The target gas (CO₂) is present in a known mixture of gases (air).
• Expected air composition: Nitrogen: 78.08% (TC = 25.6), Oxygen: 20.95% (TC = 26.1), Argon: 0.93% (TC = 17.8), Carbon dioxide: 0.04% (TC = 17). TC is expressed in mW/m.K at 25°C. The concentration of other gases in the air is too small to affect thermal conductivity.
•  Changes in thermal conductivity are solely caused by changes in CO₂ concentration.

These conditions are met in both indoor and controlled environments where CO₂ is intentionally introduced.

Thermal conductivity is primarily influenced by temperature, with humidity and atmospheric pressure having smaller effects. The Sensirion STC31-C sensor lets you input temperature, relative humidity (RH), and pressure to enhance measurement accuracy, while the STCC4 sensor supports inputs for RH and temperature.

STCC4 Sensor

The STCC4 sensor is well-suited for measuring CO₂ concentration in indoor environments, optimized for a range of 400–5,000 ppm (0.04–0.5%), and is expected to be available in Q4 2024.

Typical applications

• Indoor air quality monitors, smart thermostats, HVAC systems, and more.

Preliminary specifications

• CO2 measurement range: 400–5,000 ppm
• Accuracy: ±(100 ppm + 10%) of the measured value
• Supply voltage: 3.3 V
• Average supply current: 850 uA, max. supply current: 5 mA
• Interface: I²C
• Dimensions (L x W x H): 4 x 3 x 1.2 mm

STC31-C Sensor

The STC31-C sensor is suitable for measuring CO₂ concentrations ranging from 1% to 100%, commonly found in controlled atmospheres.

Typical applications

• Perishable Goods Transportation. CO₂ is typically maintained between 1–20%.
• Bioreactors and Incubators. Maintaining constant CO₂ levels and humidity for optimal cell cultivation.
• Supermarkets/Industry. Used in CO₂ cooling systems and fire suppression systems.
• Winemaking/Brewing Industry. Fermentation testing probes, operator safety.
• Breath Testing: Provides a simple yes/no confirmation if a sample comes from human breath.
• Breath Analysis: Precise CO₂ measurement in breath is possible but requires significant development effort. Sensirion is able to support large-scale projects involving over 6,000 sensors.

STC31-C specifications

• 4 selectable environment models: 0–40% CO₂ in air, 0–100% CO₂ in air, 0–40% CO₂ in N₂, and 0–100% CO₂ in N₂.
• Accuracy: ±0.2–2.0% (refer to datasheet for details)
• Ultra-low power consumption
• Measurement mode: 3 mA typical at 3.3V
• Idle mode: 50 µA typical at 3.3V
• Sleep mode: 1 µA maximum at 3.3V
• Fast response time (τ63): < 0.5 seconds
• I²C interface
• 4 configurable I²C addresses via a resistor between ADDR pin and VDD
• Backward compatible with STC31
• 12-QFN package, 3.5 x 3 x 1 mm

We’re excited to offer both the STCC4 and STC31-C gas sensors from Sensirion as part of our product range.  The STC31-C sensor is available immediately from our warehouse for your applications. The STCC4 sensor is expected to be available by Q4 2024, as per the manufacturer’s timeline.