Dual Beam Infrared Spectrometer is used for recording infrared absorption/reflection spectrum in range of 4000-400 and qualitative & quantitative analysis for substance information from the spectrum recorded. It is an important tool for substance structure analysis in many fields like petroleum, chemical industry, medicine, sanitation, food stuffs, paper making, environment monitoring and semiconductor.
Other than common zero balance type, this instrument adopts a principle of direct-proportioned computer record. Figure 3-1 is an illustration of its working principle.
The light from source is divided into two energy-equal beams. One is sample beam S which passes through sample; another one R is for reference. After passing through the sample room and then photometer, the two beams are modulated by sector mirror with frequency of 10Hz and turned into alternating signals, then combined and shot into monochromator through entrance slit. The combined beam is parallelly projected onto a grating by off-axis paraboloidal mirror, dispersed and out through the exit slit. A filter is used to filtrate high order spectrum. Then the beams are focused on the acceptance surface of detector by ellipsoidal mirror.