Design Of SF₆ Gas Detector-based On NDIR Technology

SF₆ gas is widely used in power systems because of its high stability,strong electrical insulation strength and excellent arc extinguishing performance.However,the leakage of SF₆ gas is a ubiquitous and unavoidable problem due to the differences in manufacturing processes,production,installation and the aging of equipment.Once the SF₆ gas leak occurs,it will cause huge losses to the state’s property,even seriously endanger the health of the workers.Therefore,it is of great significance to the development of SF ₆ gas concentration detection system.Based on the theory of infrared spectrum absorption,this thesis designed a set of SF₆gas concentration detection system based on NDIR（non-dispersive infrared）technology with small size and high measurement accuracy.The main research contents are as follows:（1）The measurement theory of SF₆ gas concentration based on infrared spectrum absorption was elaborated in detail,and the measurement advantages of non-dispersive infrared technology were compared with the common measurement methods of SF₆ gas concentration.（2）A set of SF₆ gas concentration measurement system was designed and completed,including device selection,circuit system,GUI（Graphical User Interface）design,and temperature compensation algorithm design.Among them,a pyroelectric detector for SF₆gas with dual-channel was used,the output electrical signal of dual-channel,including the signal channel and the reference channel,can inhibit the influence of unstable infrared light,dust and other factors;In circuit systems,combined with the characteristics of pyroelectric detectors with low peak-to-peak of output AC signal,high DC bias,and low signal-to-noise ratio,two-order bandpass filters and high-gain instrumentation amplifiers were designed to perfectly extract the voltage signals of detector,which has a high signal-to-noise ratio;The minimum system was designed by using STM32microcontroller,as the control center of the slave computer and data communication with the host computer;GUI could complete the real-time drawing of the channel curve and concentration curve,display temperature,save the picture and other functions;Lambert-Beer’s law was corrected,and the algorithm of temperature compensation was proposed to correct the effect of temperature on gas concentration measurements.（3）The testing of SF₆ gas concentration detection system was completed,including circuit test,concentration calibration test and temperature change test.The experimental results showed that the detection system designed in thesis can accurately measure SF₆ gas in the range of 0-10000ppm.The repeatability and stability of the measurement could meet the actual requirements.