Fiber optic reflectance probes

J.H. Cho, P.J. Gemperline, P.K. Aldridge, S.S. Sekulic, Effective mass sampled by NIR fiber-optic reflectance probes in blending processes. Anal Chim. Acta, 348, 303-310 (1997). 

Herbert, P.M., Gauthier, T.A., Briens, C.L., and Bergougnou, M.A., "Application of Fiber Optic Reflection Probes to the Measurement of Local Particle Velocity and Concentration in Gas—Solid Flow", Powder Tech., 80, 243 (1994). 

Having established that the multi-wavelength transmission techniques offer a number of advantages, the Uv-vis reflectance spectra from concentrated polystyrene lattices have been recorded using fiber optics reflection probes. Although some averaging of the individual particle properties can be expected, reliable calibration and estimation of the particle properties is possible, since discrimination to the desired particle properties is found as it will be shown below. 

Fiber optic spectrometers with reflectance probes build an additional degree of flexibility into reflectance spectroelectrochemical measurements. Fiber optic reflectance probes are typically made of multiple fiber optics which direct the light from the source to the sample surrounding one or more fiber optics which collect the reflected light and direct it to the detector. These fibers are usually combined within a single cable which is bifurcated... 

Herbert PM, Gauthier TA, Briens CL, Bergougnou MA. Application of fiber optic reflection probes to the measurement of local particle velocity and concentration in gas solid flow. Powder Technol 80 243-252, 1994. 

Reflective probes may be used over the entire rang of particle concentrations, from extremely dilute flows to the fixed bed state for several powder types in gas or liquid media, once they have been suitably calibrated [63, 85, 166, 238]. These probes are also nearly free of interference by temperature, humidity, electrostatics and electromagnetic fields. Lischer and Louge [116] developed a reflective F-OPT specifically for measuring solids concentration. In the fiber optical reflection probe developed by Hartge et al. [82], the emitted light from a laser diode reaches the... 

Along with the ever increasing demand for on-line or in-line particle characterization in process control, requests for direct measurements of particles in pipelines or reactors are on the rise. In process control, any bias of the characterization method or precise physical meaning of the parameters determined are not of the utmost importance. Robusmess, reliability, and precision of measurement are often the primary concerns. Besides focused beam reflectance and fiber optical PCS probe, back scattering intensity measurement is among the optical techniques preferred for in-process measurement due to the obvious reasons that when the concentration of a suspension is high, the... 

Direct photography of drops in done with the use of fiber optic probes using either direct or reflected light. StiU or video pictures can be obtained for detailed analysis. The light transmittance method uses three components a light source to provide a uniform collimated beam, a sensitive light detector, and an electronic circuit to measure the amplified output of the detector. The ratio of incident light intensity to transmitted intensity is related to interfacial area per unit volume. 

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

A particularly difficult problem in microwave processing is the correct measurement of the reaction temperature during the irradiation phase. Classical temperature sensors (thermometers, thermocouples) will fail since they will couple with the electromagnetic field. Temperature measurement can be achieved either by means of an immersed temperature probe (fiber-optic or gas-balloon thermometer) or on the outer surface of the reaction vessels by means of a remote IR sensor. Due to the volumetric character of microwave heating, the surface temperature of the reaction vessel will not always reflect the actual temperature inside the vessel [7]. 

Design and selection of the sample interface is vital to provide the best-quahty data for an analysis. The sample interface may be located in the sample cavity of a spectrophotometer, as in the cases of laboratory cuvettes, vials, and flow cells. The sample interface may also be fiber-coupled and located closer to the process. Fiber-optic sample interfaces include flow cells, insertion probes, and reflectance probes. 

In the worse case, where either sample temperature, pressure or reactor integrity issues make it impossible to do otherwise, it may be necessary to consider a direct in situ fiber-optic transmission or diffuse reflectance probe. However, this should be considered the position of last resort. Probe retraction devices are expensive, and an in situ probe is both vulnerable to fouling and allows for no effective sample temperature control. Having said that, the process chemical applications that normally require this configuration often have rather simple chemometric modeling development requirements, and the configuration has been used with success. 

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