Near infrared (NIR) fiber optic spectroscopic analyzers are being used widely in the process industry. One of the long- standing issues with such analyzers is the ability to transfer calibrations from one analyzer to another and from an analyzer to itself after repair. The most frequently services parts of a spectrometer are the lamp and the probe. This paper will examine calibration issues related to probe design, probe to probe uniformity, and the interaction of the probe, spectrometer and fiber combination. Specifically, what impact does transmission, spectral features, vibration sensitivity, pathlength, window wedging, and other probe characteristics have on the spectroscopic system performance and transferability.
A new flow-through high-pressure optical cell, with unique design features, allows spectroscopic monitoring of process streams. The novel design features no windows, has no dead volume and minimizes sample perturbations. A monolithic sapphire block serves as both pressure containment and optical material. The sample chamber is an integral part of the sapphire; thus creating the small, no dead volume sample chamber, while maintaining high optical throughput. Using an auxiliary optical interface adapter, this flow probe can be easily coupled to a fiber optic based spectrometer. The probe is ideally suited for low volume applications, such as pilot plants, GCs, etc. Being of sapphire construction, the probe functions from UV through the near-infrared and has an equivalent pathlength of 2.1 mm. The application to spectral measurements in the near-infrared and visible regions will be illustrated. Direct spectral comparisons to samples run in the probe and in a 2 mm cuvette will be made.