Data Acquisition And Processing Logic Design Of The Laser Gas Monitor

One of the outstanding issues in the world is the pollution from the emission of the harmfulgases in industrial production. Monitoring accurately and in real time the concentration of thesereleased gases is important and urgent.In this thesis, an signal reception and processing system used in FPGA platform laser gasmonitoring instrument was designed in order timely to monitor the concentration of methane gasreleased from industrial production.Bill-Lambert’s law, the basic theory of the infrared absorption spectrum for gas molecules, andtunable semiconductor technology were used first. Meanwhile, analyse in depth the mechanism andstructure of digital signal FIR, digital filter algorithms and digital lock-in amplifier. based on thetheory of the digital lock-in amplifier, a modified theoretical derivation was proposed to improve thealgorithm, and a theoretical analysis and MATLAB simulation based on an orthogonal square wavedigital lock-in amplifier were given.After the theoretical analysis and MATLAB simulation, an experimental system platform wasbuilt up, based on the combination of FPGA chip processor and high-speed AD acquisition system.Each functional module in FPGA device was made a logic design and carried a timing simulation,which completed the signal processing, storage and transmission. To meet the requirements to thedesign of digital filter, an improved method was suggested to use repeatedly packet multiplexingembedded with internal FPGA hardware multiplier.Finally, the built-up system platform was tested with a methane concentration set at40%. Thetest results were compared with the data from MATLAB simulation and it was found that FPGAimplementation with a signal reception and digital signal processing system in the laser gas detectoris feasible.