Sensirion SCD40
Compact photoacoustic NDIR CO₂ sensor for indoor air quality and HVAC monitoring.
Key Specifications
How Photoacoustic CO₂ Sensing Works
The sensor modulates infrared light near a CO₂ absorption wavelength. When the gas absorbs the light, periodic heating creates a small pressure or acoustic signal. An acoustic detector measures the signal and the device’s electronics estimate carbon dioxide concentration, applying compensation and calibration as specified by the manufacturer.
Integration Considerations
Verify measurement conditions, automatic baseline correction requirements, installation environment, power peaks, bus communications, humidity and pressure effects, and manufacturer lifecycle status before product selection. Accuracy ranges should not be confused with digital reporting or output ranges.
Official Manufacturer Source
Product information and lifecycle status should be checked against the current manufacturer listing.
View SCD40 official product page →AirAlign is an independent technical information resource and is not affiliated with Sensirion. Specifications and product availability can change.
SCD40 — economical photoacoustic CO₂ + RH/T — model-specific datasheet review
These original manufacturer specifications are bounded to their stated measurement conditions. Output coding, calibrated precision, voltage domains, firmware and lifecycle status are not universal across variants.
| Property | Official model specification | Engineering limitation |
|---|---|---|
| Measurement principle | Photoacoustic NDIR (PASens) CO₂ with embedded SHT4x RH/T compensation | True CO₂ molecules; not an eCO₂ estimate from a VOC sensor. |
| Calibrated CO₂ accuracy band | 400–2,000 ppm, ±(50 ppm + 5% of reading) | At 1,000 ppm this means approximately ±100 ppm under reference conditions. |
| Digital output range | 0–40,000 ppm, wider than specified accuracy band | Do not claim metrologically warranted accuracy throughout full digital-output range. |
| Response / sampling | τ63 around 60 s; periodic 5-second sampling minimum | Sampling faster than sensor physics cannot eliminate chamber response delay. |
| Electrical supply | 2.4–5.5 V; peak up to 205 mA, typical periodic current ~15 mA at 3.3 V | A battery design must handle measurement pulses, not only average draw. |
| Bus and assembly | I²C, surface mount, 10.1 × 10.1 × 6.5 mm | Check pullup voltage, host bus capacitance and mounting stress. |
| Environment | −10 to +60 °C; 0–95% RH non-condensing | Humidity, self-heating and thermal gradients bias RH/T channels. |
Selection, calibration and application
Automatic self-calibration uses a recurring fresh-air baseline; a continuously occupied, sealed room may never reach outdoor CO₂ level, so the algorithm assumptions should be checked and manual reference calibration documented when appropriate. After soldering or rough handling the datasheet advises recovery via ASC or FRC after suitable stabilization. Compare SCD40 with SCD41 and SCD43 before selecting: the ±(50 ppm + 5%) SCD40 tolerance should not be replaced with the better SCD43 ±(30 ppm + 3%) claim. Correct host timing, pressure compensation and temperature offset are part of accurate measurement.
Original manufacturer references: SCD40 — economical photoacoustic CO₂ + RH/T official product data. Latest order code, precise calibrated concentration band and regulatory requirements must be checked before deploying a sensing or safety solution.
AirAlign technical editorial review, 25 October 2026. Not a substitute for current device-specific measurement calibration or certificates.