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Concept and set-up of an IR-gas sensor construction kit

The paper presents an approach to a cost-efficient modularly built non-dispersive optical IR-gas sensor (NDIR) based on a construction kit. The modularity of the approach offers several advantages: First of all it allows for an adaptation of the performance of the gas sensor to individual specifications by choosing the suitable modular components. The sensitivity of the sensor e.g. can be altered by selecting a source which emits a favorable wavelength spectrum with respect to the absorption spectrum of the gas to be measured or by tuning the measuring distance (ray path inside the medium to be measured). Furthermore the developed approach is very well suited to be used in teaching. Together with students a construction kit on basis of an optical free space system was developed and partly implemented to be further used as a teaching and training aid for bachelor and master students at our institute. The components of the construction kit are interchangeable and freely fixable on a base plate. The components are classified into five groups: sources, reflectors, detectors, gas feed, and analysis cell. Source, detector, and the positions of the components are fundamental to experiment and test different configurations and beam paths. The reflectors are implemented by an aluminum coated adhesive foil, mounted onto a support structure fabricated by additive manufacturing. This approach allows derivation of the reflecting surface geometry from the optical design tool and generating the 3D-printing files by applying related design rules. The rapid fabrication process and the adjustment of the modules on the base plate allow rapid, almost LEGO®-like, experimental assessment of design ideas. Subject of this paper is modeling, design, and optimization of the reflective optical components, as well as of the optical subsystem. The realization of a sample set-up used as a teaching aid and the optical measurement of the beam path in comparison to the simulation results are shown as well.