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 (LDC) with a CO2 indicator coating (heteropolysiloxane), a capacitive humidity sensor and (optional) 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 algorithm 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 8 months. (C) 1999 Elsevier Science S.A. All rights reserved.