Bomem-GRAMS User's Guide

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Appendix D Glossary To avoid channel spectrum in transmission cells with a small optical pathlength, a wedge in the sample path is used to prevent parallelism of the two windows. coadded spectrum The spectrum resulting from averaging, on a point-by-point basis, a number of spectra or interferograms. Coaddition is used to increase the signal-tonoise ratio of a spectrum. desiccant A substance used as a drying agent. detector A device in a spectrometer that produces an electrical signal that is proportional to the intensity of the light striking it. detector cut-off The frequency or wavelength at lower end of the spectral range. detector saturation A condition of the detector whereby an increase in the light intensity striking it no longer produces a linearly proportional change in the output signal. This is a nonlinear condition and can cause Fourier stray light. D-star (D*) A value used to designate the specific detectivity. This is a performance measure independent of detector size. The higher is the D* value, the better is the detector. 1 2 D* = (A × ∆f ) D where A is the sensitive area ∆f is the bandwidth frequencies D is the reciprocal of noise equivalent power (NEP) factor In analysis using the PLS algorithm, one of a series of synthetic spectra which represent the most common variations in a given set of spectra (also known as latent vectors, characteristic vectors, spectral loadings, loading vectors, principal components, or variation spectra.). 50 Bomem-GRAMS User's Guide
Appendix D Glossary Fast Fourier transform (FFT) A mathematical algorithm for efficient calculation of the Fourier transform. Fourier transform A mathematical function that transforms the time-dependent information contained in the interferogram into the corresponding optical spectrum. F-ratio An indicator of spectral residual after modeling that can help detect whether an abnormal condition has occurred during analysis. The F-ratio should normally be low (typically less than 10, depending on the application). An F-ratio higher than average may indicate that the wrong material is being analyzed or that there is a problem with the system. FT-IR Fourier transform infrared. FT-MIR Fourier transform mid-infrared. FT-NIR Fourier transform near-infrared. grab sample A sample extracted from the process at the precise time that a spectrum is recorded. Laboratory analysis of the grab sample using a primary method is used to validate or improve the analyzer calibration. hygroscopic Able to absorb moisture from the atmosphere. hygroscopic optical component An optical component made of hygroscopic material. Such optical components can be damaged if exposed to humidity because they can absorb moisture from the atmosphere. Bomem-GRAMS User's Guide 51
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Bomem-GRAMS User's Guide This manua
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T ABLE OF CONTENTS About this Manua
Page 9: ABOUT THIS M ANUAL Audience a This
Page 12 and 13: Section 1.1 Check the signal Figure
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Page 16 and 17: Section 1.3 Acquire a sample spectr
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Page 26 and 27: Section 4.1 Description Parameter S
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Page 32 and 33: Section 4.1 Description Threshold d
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Page 42 and 43: Appendix A Apodization Functions Na
Page 44 and 45: Appendix B Array Basic Interface Ar
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Page 59: Appendix D Glossary blank sample A
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Page 76: Analytical and Advanced Solutions 5
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