| In the normal nondestructive testing technology, eddy current testing is still not fully exploited in contrast with the other methods. There are some reasons to this situation. First and foremost, eddy real-time imaging is very difficult. At present time the main eddy imaging technologies are Impedance C scan imaging technology, Layer-divided imaging technology and Magic-light converting imaging technology. An eddy current detecting and imaging apparatus has been developed in this paper. It will be used to detect the imbedded metal test piece. Imaging technology of this paper is based on Impedance C scan technology, and some improvements have been made, the DSP (digital signal processor) has been used, the scanning speed has been improved greatly and the time of signal processing and delay have been shortened enormously. The aim of real-time imaging and orientation has been obtained.This system of eddy current detecting and imaging is made up of the three Figure 1 The principle frame of the system parts: signal sampling of eddy current, the pretreatment system and interface circuit and imaging processing system based on computer. The principle frame of this system is figure 1.The working process as follows, sampling signal which comes from eddy current signal sampling system, in one hand, is sent to high signal processor ADSP21060, in the other hand, it is sent to the controller, and it will control the sampling system by feedback and send the signal to the DSP after been processed, simultaneously, the controller will transfer the signal to the computer for imaging processing by asynchronous communication. The DSP mainly do the job of pretreatment and the control of the controller, during the pretreatment, it will realize A/D conversion, wave filtering, FFT and construct the mapping relation of amplitude and phase and the coordinate (x, y) of scanning sensors. It prepares for later imaging The signal sampling system is very important .The principle figure of signal sampling system of eddy current is figure 2Figure 2 The principle figure of signal sampling system of eddy currentThe working progress as follows, the signal from line-array sensors is first amplified by the preamplifier groups, the X-R separator separates them into two vertical channels and get the real part and the virtual part of impedance signal so that they can be processed separately, then selected two channels and transferred by the AD7502, then they will be transferred to the DSP for pretreatment. The DSP will pretreat the corresponding relationship between amplitude and phase of the real part and virtual part, and the relationship between them and the coordinate of scanning system. The AD7502 make logic switch under the control of DSP, it can select two channels at the same time, so the preamplifier also has two channels input and output. This paper is based on detecting the reality. So the structure form of the eddy current sensor id very different from the traditional inspection sensor. The sensor has been modificated and designed in a new way. The array structure of multi-processors has been adapted.The ADSP21060 chip has been adapted in order to realize the real time signal processing and imaging. There is a high speed data signal acquisition and processing circuit with ideal and flexible data interface in this paper. Although ADSP21060 has serial port itself, it has especial difficulty in the communication with the computer. In this paper a serial communication controller (PC16550D) is used to connect the serial port. PC16550D is the universal asynchronous communication chip made by National Semiconductor Company. To meet the requirement of the communication in real-time processing, PC16550D is used to implement high speed serial interface communication of system. To content the requirement of the communication system in real time processing, we can implement high speed serial interface communication of the system, meanwhile the control ability of system communication interface can be intensified.
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