Infrared spectroscopy is an instrument for the analysis of molecular structure and chemical composition by using the absorption characteristics of substances to infrared radiation of different wavelengths. Infrared spectroscopy is usually composed of light source, monochromator, detector and computer processing information system. According to the different spectroscopic devices, it can be divided into dispersion type and interference type. For a dispersive dual-path optical zero-position equilibrium infrared spectrophotometer, when the sample absorbs certain frequency of infrared radiation, the vibrational energy level of the molecule transits, and the corresponding frequency of light in the transmitted beam is weakened, resulting in the intensity difference of the corresponding radiation between the reference light path and the sample light path, thus obtaining the infrared of the measured sample.