The Model 15i analyzer operates on the principle that hydrogen chloride (HCl) absorbs infrared radiation at a wavelength of 3.4 microns. Because infrared absorption is a nonlinear measurement technique, it is necessary for the instrument electronics to transform the basic analyzer signal into a linear output. The instrument uses an exact calibration curve to accurately linearize the instrument output over any range up to a concentration of 5000ppm in emissions from a source.
