Novel NDIR CO/sub 2/ sensor for indoor air quality monitoring

This paper describes NDIR CO/sub 2/ gas sensor with novel optical cavities and two elliptical mirrors that are optimized for the optical path and light intensity. The new structures have two distinct features: one is focusing of infrared (IR) light onto the detector with the minimum cavity volume, and the other is an increased optical path length in order to enhance the sensitivity and accuracy. The developed sensor module shows about 360 mV voltage differences from 0 to 2000 ppm CO/sub 2/ concentration with 18,000 amplification gain. The response time of sensor module is around 30 sec.