NDIR instrumentation design for Carbon Dioxide gas sensing

In this thesis the development of a single pass non-dispersive infrared (NDIR) CO2 gas sensor with a path length of 30mm and with a lowest level CO2 detectivity of 20 ppm is described. A single pass NDIR CO2 sensor was developed in order to better understand the effect of the different sensor components i.e. the infrared source, thermal detector and the interference filter has on the NDIR CO2 gas sensor’s sensing ability for the industrial gas sensing application. . The study of various IR sources, detectors and filters has resulted in developing methodology that can be used for characterising IR sources detectors and filters from an application point of view. The obtained result from such application specific characterisation shows a more realistic measure of the NDIR CO2 sensor’s individual components performance characteristic, than what is quoted by the manufacturer of the IR sources, detectors and filters. The developed characterisation methodology is novel in its own right as such methodology currently to the author’s knowledge does not exist in the available literature. In order to better understand the effect of different infrared (IR) source, detectors and filters four different types of IR sources (microbulb, membrane type source, IR-LED source and ICX 2Dmetallo photonic crystal sources/detector pair), three different type of IR detectors Pyroelectric detectors, Thermopile detectors and 2D-metallo photonic crystal source/detector pair and two interference filters were investigated. A new amplitude modulation (AM) scheme was developed for driving the 2D-metallo photonic crystal device as a detector. This has resulted in an improvement of the 2D-metallo photonic crystal devices detectivity by a factor of 102 compared to the standard / conventional / recommended scheme. Demonstrations of the performance of the developed NDIR CO2 gas sensor are also shown in this thesis.