Liquid Level Detection And Estimation Method Based On Acoustic Resonance Principle

The fluid level detection plays an important role in the production,processing,transportation,reserve calculation,state and alarm monitoring of modern industry system.It is widely used in petroleum,chemical industry,sewage treatment and other related fields.Based on error analysis of acoustic resonance fluid level detection principle,Belief Rule Base and Evidential Reasoning are respectively used to reduce the theoretical error caused by the approximate formula of the acoustic resonance-based level detection and systematic error caused by transmit/receive acoustic wave system,which effectively improve the accuracy of the acoustic resonance fluid level detection.The main work is as follows:(1)The analysis of acoustic resonance-based fluid level detection principle.It analyzes the principles of initial acoustic resonance fluid level detection method and acoustic resonance fluid level detection method in a special frequency range.The common advantage of the two methods is the use of low frequency sound wave,which effectively avoids the occurrence of parasitic reflections in the ultrasonic measurement.Detect range of the former is limited by the initial resonance frequency(RF)and the sensitivity of the receiver(microphone).The latter uses a group of RFs generated in a given frequency range instead of single initial RF to calculate fluid level height so as to overcome the sensitivity problem of microphone,and improves range,accuracy and speed of detection.(2)Fluid level detection error compensation method based on belief rule base reasoning.In order to reduce the error caused by the approximate principle of acoustic resonance fluid level detection in a special frequency range,a BRB error compensator is designed.It is proposed to model the complex nonlinear relationships between the multiple parameters of resonance waves(standing waves)and error compensation values.When the values of the input parameters are obtained at a certain fluid level height,the belief rules activated by the inputs are fused by the evidential reasoning algorithm.Error compensation values can be calculated from the fused result,which can be used to effectively compensate for the detected height.(3)Fluid level estimation method based on evidential reasoning(ER).In order to reduce the error caused by transmit/receive acoustic wave system in acoustic resonance fluid level detection principle in a special frequency range,state estimation method based on ER fusion is designed.It establishes a two dimensional dynamic system model of the wavelength of standing waves.The random set description of evidence and the extension principle of random set are used to obtain state/observation evidence of the wavelength of standing waves.The ER rule is used to fuse two pieces of evidence,and then the fluid level can be calculated from the fused result based on Pignistic expectation.The above two error processing methods of fluid level detection illustrate their effectiveness by comparing with the existing error processing method in the corresponding fluid level experiments.