Research On ECT System Based On FPGA

Electrical Capacitance Tomography(ECT)is a new type of visual detection technology developed in recent decades because of its low cost,fast response,easy portability,no radiation,no intrusion,and robustness.And other advantages,is widely used in industrial fields such as flame combustion and fluidized bed monitoring.As the industry develops faster and faster,it also places higher and higher requirements on the measurement accuracy and speed of ECT technology.In order to improve the data acquisition rate of ECT system,this paper studies the microcapacitance measurement circuit in capacitance tomography,and introduces the measurement circuit of triangular wave excitation into the system to construct a set of ECT imaging system,which effectively improves the system data acquisition rate.The gas-solid two phases were used as experimental objects to verify,and good measurement data and experimental images were obtained.The main research work and research results are as follows:1.Different capacitance measurement circuits are compared and analyzed.A method of using triangular wave instead of traditional sine wave as excitation signal is proposed.The differential characteristics of C/V conversion circuit are used to make the output as square wave signal and the amplitude and capacitance to be measured.The values are linear.Since it does not require a phase sensitive demodulation link and the response time of the measurement circuit is reduced,the capacitance measurement rate is greatly improved.2.Based on the Xilinx Spartan-6 FPGA chip,a digital data acquisition system is designed and implemented.The system reads the triangular wave digital signal in the ROM from the FPGA,generates the excitation signal through the external D/A conversion circuit.The programmable gain amplification widens the dynamic measurement range of the measurement circuit.The external A/D conversion circuit samples the measurement data,implements the median filtering processing of the data by using the internal logic resources of the FPGA,and then transmits and communicates with the host computer through the USB2.0.3.The system performance test and imaging experiment were carried out.The experiment proved that the system can work stably and accurately collect the capacitance data from the sensor end.Compared with the sine wave excitation measurement method,the data acquisition rate is increased to 2681 frames/second.