For this form of gas analysis, the spectral sensitivity of a broadband thermal detector is limited by an OPTICAL bandpass filter. This is DONE for the range in which the absorption bands are found for the gas to be determined. With the thermal detector, the TRANSMISSION of the measured gas mixture is determined in a defined arrangement. If the gas being searched for is not present, most of the infrared RADIATION will reach the detector and the signal will be at its MAXIMUM. If the concentration of the gas increases, absorption will also increase according to Lambert-Beer’s law, and the signal will reduce accordingly.

For this form of gas analysis, the spectral sensitivity of a broadband thermal detector is limited by an optical bandpass filter. This is done for the range in which the absorption bands are found for the gas to be determined. With the thermal detector, the transmission of the measured gas mixture is determined in a defined arrangement. If the gas being searched for is not present, most of the infrared radiation will reach the detector and the signal will be at its maximum. If the concentration of the gas increases, absorption will also increase according to Lambert-Beer’s law, and the signal will reduce accordingly.