Detection limit improvement for NDIR ethylene gas detectors using passive approaches

The influence of passive construction improvements of a NDIR ethylene gas detector on the signal intensity and the detection limits were examined. Rectangularly and conically shaped measurement chambers with and without low-cost Fresnel lenses were used. Also the influence of the choice of the applied broadband IR-sources was investigated and an equation for detection limit estimation is described. In addition three digital signal processing methods were compared with results provided by a lock-in amplifier. It was shown that the best signal intensity can be achieved using a combination of a conically shaped chamber and Fresnel lenses. The IR-radiation measurement efficiency was improved from 0.8% to 4.2% in the best case. The achieved detection limits were 34ppmv without and 25ppmv with the lock in amplifier, the noise equivalent values 6ppmv and 4ppmv respectively. These limits match roughly with the calculation results and are comparable with results obtained with white cell systems.