Superluminescent Diode-Based Multiple-Gas Sensor for NH₃ and H₂O Vapor Monitoring

An approach of superluminescent light emitting diode (SLED)-based multiple-gas sensing (NH3and H2O vapor) is proposed and demonstrated by using an absorption spectroscopy technique for emission monitoring (DeNOxprocess) applications. Such process normally occurs at temperature range of 250-400°C where significant interference effect due to H2O vapor is expected. Hence, measuring multiple gases and eliminating cross-interference effect is of great importance in sensing trace gases. In this study, an SLED-based sensor with center emission wavelength of 1530-nm region is chosen to measure the concentrations of pure NH3and H2O vapor by probing its overtone and combination bands present in this region. Detection limit for the NH3gas accounted in the case of aqua-ammonia (undiluted) is estimated to be 120 ppm ·m. A novel approach of introducing an open-space etalon in the path of the SLED beam is also proposed and demonstrated for adequate isolation from interfering species and improving the detection limit. By using an etalon with a free spectral range of 104 GHz and tuning it to appropriate wavelength, detection limit of about 22 ppm·m is attained for NH3gas sensing in the presence of H2O vapor.