Preventing industrial dust pollution is one of the important tasks of environmental protection. In order to eliminate industrial smoke pollution, first of all, we must know the amount of smoke and dust emissions. wushui.37ix.com.cndiaosurw.37ix.com.cnzhagungp.37ix.com.cnzhibanx.37ix.com.cnwalengzhi.37ix.com.cn xianweisu.37ix.com.cnTherefore, we must monitor, display and alarm the sources of smoke and dust automatically. The smoke turbidity in flue is measured by the change of light in the process of transmission in flue. If the flue turbidity increases, the light emitted by the light source is absorbed and refracted by the dust particles, and the light arriving at the photodetector decreases. Therefore, the intensity of the output signal of the photodetector can reflect the change of flue turbidity.