Development And Verification Of Visual Measurement System For Particle Distribution In Rotary Kiln

Rotary kiln is a commonly used equipment in the field of industry,mainly used for physical and chemical treatment of material particles.The materials in the rotary cylinder are fully mixed and react with the rotation of the rotary kiln.The motion state of the materials will directly affect whether the material particles can be mixed evenly,thus affecting the production efficiency.However,the material mixing process inside the rotary kiln cannot be directly seen its distribution.Therefore,it is very important to conduct visual detection of the material inside the rotary kiln.In view of the situation that the material distribution in the rotary kiln cannot be directly detected,the electrical impedance tomography(EIT)technology is used in this paper to visualize the material distribution in the rotary kiln.EIT technology is a new and fast non-invasive measurement technology,with low cost and no radiation,which is suitable for the requirements of material imaging in the industrial field.However,in this paper,the material inside the rotary kiln is visualized.The rotary kiln is constantly rotating when it is working,so the measuring instrument must be required to move together with the rotary kiln.Therefore,the volume of the measuring instrument must be small,and wireless data transmission mode must be adopted.In this paper,based on EIT imaging technology as the theoretical basis,a set of 8-electrode measurement system which can carry out dynamic imaging is developed by using FPGA.In this paper,the software and hardware systems of semi-parallel EIT detection are developed and tested.First,A sinusoidal excitation signal with adjustable amplitude and frequency is generated by the DDS module,which is converted into an analog signal by the digital signal of the D/A chip.Then,the output voltage signal is converted into A current signal by the voltage control current source module(VCCS module),and the current is injected into the excitation electrode in the target field by the selection of the multiplexer module.At this time,there are 8 channels of data acquisition and data processing to collect the voltage value on the electrode in the target field at the same time.The acquired voltage signal is converted through A/D module and transmitted to FPGA for data processing.Fourier transform(FFT)is used to demodulate the signal,and the data is sent to PC through wireless transmission for image reconstruction.Verilog hardware programming language is used to design the control logic program,and ModelSim simulation software is used to verify the accuracy of the logic program design of each module.In this paper,LCR impedance tester and EIT development system based on FPGA are used to carry out static and dynamic experiments respectively.Firstly,different excitation frequencies and different positions of the measured material in the cylindrical water tank were selected as the experimental conditions for static imaging.The imaging results of LCR impedance tester were compared with the imaging results of EIT system based on FPGA,and the comparison of static experimental results verified the accuracy and feasibility of the imaging of EIT system based on FPGA.Secondly,dynamic experiments were carried out by using the rotary test rig built.Nylon particles were used as the measuring substance of dynamic tests,and the EIT system based on FPGA was used to carry out imaging at different rotating speeds.The dynamic experiment shows that the EIT development system based on FPGA can meet the requirements of imaging the material inside the rotary kiln,so it can be applied in the industrial field.