A capacitive CO2 sensor system with suppression of the humidity interference

This paper presents a capacitive CO2 sensor system with an effective numerical suppression of the humidity interference. The system consists of an heatable interdigital capacitor (IDC) with a CO2 indicator coating (heteropolysiloxane), a ca-pacitive humidity sensor and (op-tional) a temperature sensor. The CO2 measurement range has a high resolution between 100 and 3000 ppm CO2 and covers with a lower resolution 100 - 10000 ppm CO2 (twice TLV). These specifications follow the needs of indoor air quality monitoring (e.g. for mechanical ventilation). The software algo-rithm for the humidity interference rejection can be scaled down to a microcontroller (i.e. 8051 family). A long term study results in a lifetime of the CO2 sensors of more than eight months.