Study On Magnetic Induction Tomography Conductivity Measuring System Based On FPGA

In the substances capable of conducting electricity, such as metals and solutions, the electromagnetic features will change obviously with the contents of the constituents. Electromagnetic tomography and electromagnetic measurement can acquire the electro-conductivity information of the target conductors. They have the non-contact and non-immersive features, which enable avoiding the measurement errors caused by contacts and enlarge the application fields of electromagnetic measurement technologies. This makes they have been widely used and have great prospects in the fields of industrial, medical, food safety and product quality inspection.Based on the electromagnetic measurement technology, an electromagnetic electro-conductivity measurement system has been designed with FPGA as its core, integrated with excitation source and phase detection. The system can precisely measure the electro-conductivity of the target conductor. Major work includes the items as follow:1. Electromagnetic tomography theory and electromagnetic measurement technology are studied. By analyzing the popular system models, a systematic excitation-detection dual side dual coil model is confirmed. Based on the different requirements for excitation coil and detection coil, an excitation coil with relatively uniform and large field strength, and a sensitive enough detection coil are designed.2. Based on the directional digital synthesis technology (DDS) with FPGA as its core, a relatively ideal sinusoidal signal is obtained by function simulation and timing simulation. The two-stage amplification and elliptic low-pass filter are adopted to make the signal with high stability, which works as the excitation source of the electromagnetic electro-conductivity measurement system.3. Time difference counting method and phase-locked loop technology are adopted. A systematic phase-detection function module is designed. High-precision measurement of the phase difference is achieved.4. RS232 serial communication technology is employed to make the communication between the FPGA system and the master computer. And the LABVIEW package is used to design an easily-operated human-computer interaction interface to setup the system parameters and display the results.At last, the field sensitivity distribution is analyzed, taking saline solutions with different size and electro-conductivity. At the same time, the relationship between the electro-conductivity and the phase difference of the target sample, and the size resolution of the system are also studied. The measurement results agree well with the magnetic field theory, which indicates that this system can precisely measure the electro-conductivity of the conductors.