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1、APPLICATION IN NDT OFCOMPUTER DIGITAL X-RAY REAL TIMEIMAGE SYSTEMAbstractNondestructive testing (NDT) is one of the most commonly used scientific means to detect the internal defects without damaging the tested objects, therefore it is found widely applications in the industries of mechanical, petro
2、chemical, aerospace etc. Radiographic Testing (RT) by X-ray is commonly used NDT method at present, its disadvantages are unavoidable for its long test period, high cost and environment pollution. With the development of computer technology, an emerging NDT method with digital X-ray real time image
3、(DXRTI) is found increased application in industry. This paper presents the fundamentals and applications of computer numerical image technique (CNIT) in NDT with DXRTI technique, and introduced the new developed DXRTI software XCX2000 and its applications and economic benefit in weld defects detect
4、ing for LPG Cylinders.Keywords computer, software, Real Time Image, digital images processing, X-ray, NDT1. IntroductionThe principle of NDT with DXRTI may be briefly expressed by the two conversions: After penetration of metal, X-ray signals was captured and converted into the visualized images by
5、the Image Intensifier, which is called photoelectric conversion. The visualized images was shot by very fine resolution video camera and then was converted into digital image by Image Acquisition Card , which is called A/D conversion. The digital image was processed with computer and display the pro
6、perties, dimension and location of the inside defects on screen. Finally, the defect grade was assessed according to the relevant codes and standards. The quality and effect of DXRTI is acceptably good compared with radiographic films, so that the later can be replaced by the former method. Moreover
7、, with its much higher efficiency, lower cost, better inspection effectiveness, remoter transmission and much more convenience, DXRTI has prosperous future in the field of NDT.2. System requirementsDXRTI NDT system is composed by X-ray source, image intensifier, optical channel, video camera, comput
8、er, Image Acquisition Card, image display and storage equipment(see Fig.1). The X-ray source is different from the conventional one in its constant potential, small focus and forced convection cooling system.2.1 The Computers Requirements Intel MMX166 CPU or faster, 32MB RAM, 2.0G Hard disk free spa
9、ce,2D Graphic Accelerate Card(4M video memory ), 17” SVGA Monitor, CD-R Writer.Operating System: Microsoft Windows 95 /98.Fig. 1 Block Diagram for NDT with DXRTI2.2 System Management For convenient operations, two computers can be connected to the system to form a peer to peer network, one for image
10、 acquisition and the other for image assessment, and each computer works with identical purpose. The result images are stored in the hard disk for assessment and transmitted for very long distance via internet.3. Digital image processing by computer The processing of digital images by computer inclu
11、des three parts: image acquisition, images treatment and image display。3.1 Image Acquisition X-ray from radiographic machine penetrates the test object and converted into the visible image on the screen by the image intensifier. Then the images are changed into video signals by the video camera and
12、sent to the Image Acquisition Card for digital conversion. Finally the digital images are to be processed by the computer.There are two important parameters in the image acquisition: gray scale andresolution of the images. Commonly, the A/D converter of the image acquisition is 8 bits with colors of
13、 256 gray scales. Higher resolution of the image acquisition will effectively improve the defects resolving power. The resolution of the image acquisition should be no less than 768X576 dot lines.3.2 Image Processing The main purpose of image processing is to extract specific information from the im
14、ages for comprehensive computer analysis and the identification of different images.3.2.1 Image Superposition for noise reduction It is noticed that random noise information is unavoidable in image acquisition, which is one of the important factors affecting the quality of the images. For the case o
15、f stable image acquisition, one of the effective and practical ways to eliminate the random noise is to superpose the input images continuously. Theoretically, the time dependent noise can be removed or filtered completely if sufficient frames of the images superposed. Therefore, frame superposition
16、 is commonly used in the processing of images. This method is expressed by the following equation: （1）Where, g(x, y) stands for the dot gray scale of the image, M is the total numbers of the superposed image frames, fk(x,y) is the gray scale value for the Kth frame image. The sampling test shows that the results will be satisfactory when M16. 3.2.2 Gray Scale Expand （2）Gray scale
