Appendix C Spectroscopy Background Photometric Linearity Evaluation
AA003700-01 rev. G. 2.0 55
plot of absorbance vs normalized pathlength derived from the changes in
absorbance at seven frequencies as indicated by red lines in Figure C- 1.
Photometric Linearity Evaluation
Since the spectral fidelity is more critical at high absorbance, the evaluation of
photometric linearity is done specifically at the peaks of high absorbance bands
where the transmittance is expected to be near zero. Simply attenuating the IR beam
over the full spectral range such that transmittance is near zero at all wavelength, the
blocked beam case, is a redundant test since an FTIR does not show any stray
spectral response when the sample beam is blocked.
Figure C- 2.
Absorbance vs normalized pathlength for 6 absorbance spectra at 7 frequencies
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