A capacitive CO2 sensor system with suppression of the humidity interference

This paper presents a capacitive CO2 sensor system with an effective numeri cal suppression of the humidity interference. The system consists of an hea table interdigital capacitor (LDC) with a CO2 indicator coating (heteropoly siloxane), 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., fo r mechanical ventilation). The software algorithm for the humidity interfer ence 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.