Sensirion STC31-C
Thermal-conductivity CO₂ sensor for high-range gas concentration measurement and OEM integration.
Key Specifications
Measurement Principles and Applications
Thermal conductivity CO₂ measurement senses differences in heat transport through the surrounding gas mixture. Unlike optical NDIR or photoacoustic technologies, its response depends on background gas composition and usually requires compensation for temperature, humidity and pressure. The correct calibration mixture and performance requirements vary between indoor air monitoring and high-concentration process applications.
Integration Considerations
Confirm the manufacturer’s current calibration assumptions, output range, accuracy test conditions, compensation methods, installation environment and power budget. 0–100 vol% equals 0–1,000,000 ppm, but high-range sensors are not directly interchangeable with typical IAQ CO₂ modules at 400–5,000 ppm.
Source-verified model engineering details · October 2026
STC31-C succeeds the original STC31 for high-concentration CO₂ in an air/N₂ background. Its 0–40 and 0–100 vol% selectable gas models are designed for a very different task from 400–5,000 ppm room-ventilation monitoring.
| Technical parameter | OEM detail | Engineering interpretation |
|---|---|---|
| Measurement range and output | Selectable 0–40 / 0–100 vol% CO₂ in air or N₂; calibrated I²C | One vol% equals 10,000 ppm; use suitable concentration scaling. |
| Accuracy, standard low-cross-sensitivity mode | Typically ±0.5 vol%; achievable ±0.2 to ±2.0 vol% depending on application; base ±0.2 vol% at calibration conditions | Not ±(0.2 vol% + 2% of reading). Error also varies with ambient temperature, RH and pressure. |
| Typical additional error coefficients | 0.02 vol%/°C; 0.01 vol%/%RH; 0.001 vol%/mbar away from FRC conditions | Pass credible external T/RH/pressure compensation and revalidate after environmental changes. |
| Response and consumption | τ63 <0.5 s; 2.7–5.5 V; average 50 µA, maximum 5 mA (OEM catalogue) | The chip response does not include enclosure, filter or tubing transport delay; budget startup and peak. |
Standard versus legacy measurement mode
The 2025 Sensirion datasheet recommends the newer low-cross-sensitivity mode; legacy low-noise commands remain available for older STC31 integrations. The two modes have different accuracy/compensation characteristics and must not be represented by one universal accuracy formula. Re-test gas-model command arguments and firmware when migrating an existing STC31 instrument; physical and communications compatibility does not remove the need to verify calibration.
Calibration and system suitability
After forced recalibration (FRC), ambient T, RH and pressure variations contribute to an engineering error budget. A 2025 OEM example at 10 vol% in colder, drier and lower-pressure surroundings calculates approximately ±1.4 vol% typical error, not simply the ±0.2-vol% base figure. Treat it as a process or high-fraction gas sensor, not an intrinsically certified life-safety CO₂ alarm.
Primary sources: Sensirion current catalogue; Sensirion STC31-C datasheet v3.5 (September 2025), §§1–2 and 7.
Official Technical Source
Independent AirAlign technical product listing. Actual features and lifecycle status must be checked against manufacturer documentation.