Design Of Digital Eletromagnetic Induction Measurement System

Steel industry occupies a pivotal role in Chinese basic industries, and the quality of steel directly affects Chinese economic development. In the production of steel strip, the temperature distribution and cooling rates have a significant effect on the steel microstructure and hence on final material properties, such as yield strength, tensile strength and ductility . Increasingly, steel customers require better materials in order to improve their own products and processing lines that use automatic feeding or similar techniques. Consequently, demands for higher product consistency and a greater diversity of sophisticated steel grades have increased the requirements for a new instrument to monitor the microstructure of steel during controlled cooling on a hot strip mill and hence improved instrumentation. The non-contact measurement technique based on the principle of electromagnetic induction can obtain the conductivity and permeability of the field space, because of which this method can be used to solve the problems above.In order to achieve the monitoring of steel on-line, the theory of electromagnetic induction is used in this paper, and a digital electromagnetic measurement system is designed to monitor the quality of the steel online. Some main works and conclusions are presented as following:1. One difficulty in electromagnetic induction measurement is that the excitation field also induces a signal in the sensing coil (the primary signal) and the signal due to the eddy currents in the material (the secondary signal) is normally much smaller in comparison. In order to know the change of the secondary signal which is generated by the change of the material, a digital measurement system is designed and the system is divided into some modules.2. A system based on the Xilinx Spartan-3-based FPGA (field programmable gate array) is designed, the debugging of which has been successful. It has been proved to work stably during the tests.3. High-speed data acquisition module and signal generator module are designed and implemented based on FPGA. DDS module constructed in the FPGA cooperates with external D/A to provide excitation signal. High speed A/D is implemented with hard wire logics. The two parts above have been testified to meet the design requirements. 4. The digital demodulation of the numeric series generated by the signal generator module and A/D acquisition value sequence is implemented in the FPGA. It makes full use of internal hardware multiplier and accumulator of FPGA and has the characteristics of flexible structure which can be expanded, measurement precision and high speed. The correctness of its function has been validated through the experiments.