Principle And Instrumentation Of Infrared Spectrum Measuring System Based On AOTF

With more than 100 years history, the spectral instruments and spectral analyses are widely used in Physics, Chemistry, Biology, Geology, Geophysics, Medicine and other scientific fields. To fulfill real-time analyses of gas composition and concentration in end gases of cars, flue gases, process analyses etc., a new infrared spectral detecting system is researched and designed in this paper. This infrared monochromatic system consists of AOTF (Infrared Acoustic-Optic Tunable Filter), which fills the role of dispersive element, a microminiature infrared light source and a paraboloid reflector. By using DDS (Direct Digital Synthesizer), it can realize PC-controlled wavelength auto-scanning, online infrared spectral analyses of gases. This system has following advantages: simple structure, fast measuring and low cost.This paper explains the principle of AOTF infrared spectral detecting system and completes the whole instrumentation. My thesis is described as three parts: â‘  Single chip microprocessor (SCM) controlled frequency auto-scanning, including keyboard, LCD display, SCM-PC communication, DDS-SCM interface circuit, control software for SCM. â‘¡ Correlative detecting and data acquiring system controlled by SCM; Correlative detecting system includes signal amplification, wave transformation, phase displacement and correlative detecting circuit; Data acquiring system includes A/D convert circuit (controlled by SCM), control software and data communication with PC. â‘¢ PC controlled software (object oriented programming structure) based on MFC, including auto control, data acquiring, data storage and displaying of data.Finally, the whole instrument is completely instrumented. With the development in the future, neural network, wavelet transform can be added in the PC software to analyze more gas components, such as end gases of cars, flue gases etc.