Application of NIR sensor modules for process measurements

Recent years have seen the emergence of a number of miniaturized spectrometers and spectral sensors for visible and near-infrared wavelengths. The goal for the developments has been to reduce size and cost of the instruments as well as to accomplish rugged designs with no moving parts, which could be used in most demanding environmental conditions – such as process monitoring and hand-held instruments. This paper presents background information about spectral sensors: four-wavelength sensors, the LED array spectrometer and techniques for integration of electronics for use with detector array modules. Furthermore two applications relying on spectral sensors are briefly discussed: a moisture gauge developed with Metso Paper Inc. for paper mill applications as well as a study dealing with NIR transmission measurements for process control needs in plywood production.