The problem is more serious if instruments are of different make or different models from the same manufacturer. BCRA tile data will indicate the performance of instruments but cannot identify the problem of instrument metamerism. Ideally speaking, we should have the same instrumentation everywhere if colorimetric data is to be transferred and used in multiple plants. It is related to geometry, aperture size, light source, design of integrating sphere, dispersing elements, detector system, standards used in calibration and the manufacturer’s design approach. If a company with multiple plants uses different models and different makes of instrument and uses colorimetric data for quality assurance, instrument metamerism can cause serious problems.
Gangakhedkar, in Colour Measurement, 2010 12.7.4 Problems of instrument metamerism Read moreĬolour measurement of paint films and coatings It worked, and spurred the widespread adoption of near-IR spectroscopy as an analytical method, and with it the birth of dedicated near-IR instrumentation. Under the direction of Phil Williams, the near-IR method was adopted by the Canadian Grain Commission to replace routine Kjeldahl testing. The research was complicated by the observation that components other than water contributed to the absorption profiles however, this observation was quickly turned to advantage when it was found that protein could be quantified accurately from the near-IR spectrum of wheat. The original aim of this work was to develop a convenient means to monitor the water content of agricultural products. The development of modern near-IR instrumentation was spurred by research at the US Department of Agriculture Karl Norris discovered that no commercial spectrometer of the time could provide diffuse reflectance measurements of the quality he required, and developed his own computerized near-IR spectrometer for meat analysis. This equipment provided the basis for the pioneering work of Kermit Whetzel and Wilbur Kaye, who were largely responsible for laying the foundation of analytical near-IR spectroscopy. The idea of a spectrometer dedicated to near-IR spectroscopy is relatively recent, and the early commercial near-IR instruments were simply UV-visible (or mid-infrared) spectrometers fitted with an additional detector and occasionally a second grating blazed for the near-IR. This signalled the discovery of a ‘non-visible spectrum’, and coincidentally of the first near-IR spectrometer. To his surprise, the thermometer not only registered heat, but a higher temperature than that found in the visible region. Having first measured the distribution of radiant heat across the visible region, he then took the unprecedented step of moving the thermometer to a position beyond the red end of the spectrum. In 1800, William Herschel assembled a spectrometer in which the Sun served as the source of radiation, a prism as the dispersing element, and a thermometer as the detector. Mantsch, in Encyclopedia of Spectroscopy and Spectrometry, 1999 Historical development This is because of the need to rotate the grating in discrete increments, where the detector captures the output at each position. Scanning a spectrum with this type of instrument is relatively slow, usually of the order of several minutes.
Also, knowledge of the total beam angle or solid angle of emission of the source under investigation is important since this parameter could determine the necessary field of view for the measuring instrument.
#Difference between angular and linear dispersio plus
These will be determined by the slit width and the specification of the grating in use, plus the type of detector employed in the output optics. Important specifications which will need to be assessed for a specific application will be the wavelength range of the instrument and the resolution (the smallest resolvable spectral element which the instrument can detect). The function of the instrument can be broken down into steps: Input-collection optics to assure proper collection geometry, the dispersing element to break the light flux into its spectral constituents, a detector to measure the amount of flux and a means of processing and displaying the output signal. Here the dispersing element is a diffraction grating which is rotated to illuminate the detector in discrete steps.
Figure 7.6( Ruff, 1991 ) illustrates the basic components of the traditional spectroradiometer.
0 kommentar(er)
