Design Of Excitation Signal Source For Eddy Current Testing System Based On DDS

Eddy current testing is a kind of nondestructive testing technology developed quickly in recent years, which has been used in several industrial fields, especially in ship industry. A typical eddy current testing system is composed of the excitation signal source, the magnetic field measure devices and the signal sampling and processing system. In eddy current testing system, the excitation signal source produces sine or pulse signal to excite the probe of eddy current sensors. The excitation signal source is one of the key parts which affect system performance. The traditional eddy current testing system usually takes LC or RC oscillation circuit as excitation signal source. However, with the development of eddy current testing technology, analog signal source can not meet the requirements of eddy current testing gradually. Direct digital frequency synthesis is a kind of frequency synthesis technology developed quickly recently, whose primary advantages are fine frequency resolution, fast switching speed, and high signal purity. Using DDS technology to design excitation signal source for eddy current testing system can meet the requirements.Based on deeply analyzing basic principle and spectrum structure of DDS, and combined with the requirements of eddy current testing, a DDS system based on MCU and CPLD (Complex Programmable Logic Device) has been designed. In this paper, the MCU W77E058 of Winbond Corporation is selected as the master controlling core, which used C51 language to design programs to compute DDS control words and manage interface circuits such as man-machine interface, serial port interface and so on; the CPLD chip EPM7128LS84-15 is selected to realize functions of DDS such as phase accumulator and address latch unit which is designed in Quartusâ…¡using VHDL; the touch screen is chosen as man-machine interface with friendly interface and convenient operation. In addition, the upper computer software is designed in Visual C++ 6.0, which can refresh waveform data in ROM real-timely. This DDS system can produce normal waveform such as sine, square, triangle and output arbitrary waveform. In this paper, signal waveforms and parameters of DDS were tested and analysed.In this paper, the pre-research work has been completed, which has designed an excitation signal source prototype used in eddy current testing system. Experiment shows that this system can satisfy the requirements of eddy current testing in laboratory conditions. In the end of this paper, some suggestions are proposed to further improve the result of excitation signal source for eddy current testing.