Fusion Method With Interval Focal Element-type Evidence And Its Application In Liquid Level Measurement

Liquid level measurement plays an important role in industrial/engineering system condition monitoring.The corresponding measurement methods have been widely used in chemical,nuclear reaction,sewage treatment,geological disaster monitoring and other fields.The liquid level measurement method based on acoustic resonance overcomes the parasitic reflection problem existing in ultrasonic liquid level measurement,but in imperfect measuring environment with various noises,there is a problem that some resonance frequency points are inevitably missed.For solving this problem,this paper uses the evidence theory(Dempster-Shafer theory)to model the uncertain observation information(acoustic resonance frequency value),and adopts the recursive observation evidence approximation fusion method to supplement the missed resonance frequency points and improve the liquid level measurement accuracy.The main tasks are as follows:(1)Analysis of the principle of acoustic resonance liquid level measurement.The basic principle of acoustic resonance measurement is mainly analyzed.The method effectively overcomes the parasitic reflection problem existing in the ultrasonic liquid level measuring method,but the method is limited by the sensitivity of the microphone sensor and the measuring range is short.Based on this method,a liquid level based on acoustic resonance in a special frequency range is used to transmit sweep signal in a special frequency range and generate the composite wave which is processed by a fast detection method of the resonance frequency point.As a result,the liquid level is calculated by the detected resonance frequency sequence.This method improves the measurement range and measurement accuracy.(2)Approximate reduction and fusion methods of interval focal element evidence.For the "focal element explosion" problem existing in the "point value focal element type" evidence combination process,there are some methods for dealing with it in order to reduce the number of focal elements.However,there are few research results on the "focal element explosion" problem in "interval focal element type" evidence.Therefore,this paper presents an approximate reduction method of interval focal element evidence based on evidence redundancy analysis.In addition,the effectiveness of this method is proved by numerical examples and application in liquid level measurement.(3)Acoustic resonance liquid level measurement method based on recursive observation evidence approximate fusion method.Due to the influence of ambient noise,the acoustic resonance liquid level measurement method has a problem of missing the resonance frequency points.To solve this problem,the random fuzzy variable(RFV)is used to construct the interval-type focal element to model the uncertain information existing in the observation.When the construction of the interval focal element evidence is completed,the recursive observation evidence approximate fusion method is used to fuse the interval focal element evidence based on the work in(2).With the proposed method,the fusion process can naturally realize the detection and addition of the missed resonance frequency points,enhance the anti-jamming capability of the measurement system,and improve the measurement accuracy of the liquid level measurement system.