The traits and application of X ray digitized inspection system

The traits and application of X ray digitized inspection system 

Along with development and popularization of computer technology ,now it has been in digitized time。

X ray nondestructive flaw detection has been used for hundreds of years in industry area as a normal nondestructive testing method，X ray nondestructive flaw detection usually use film camera as main method,it has no way to satisfy current requirements of fast develop production and fierce competition on testing speed and costs。After decades of years of development,a totally new X ray nondestructive detection method -X ray digitized real time imagining detecting technology has been more mature and successfully apply to Chinese action。The main feature of X ray digitized real time imagining detecting technology is that it doesn’t need film camera，this is the same technology as digital camera can replace common camera。  

The carrier of Detecting results is digital picture，It marks Chinese X ray detecting technology  has entered a no film era，It is a revolution of nondestructive testing technology。

1.1 atom and bit

A mark of Industrialization era-atom。Steel is the mark of industrialization, the basic material of constituting steel is atom。

The mark of Digitized time is bit。The distinction of digitization is digital coding technique 。The binary digital coding method is made up of “0” and “1”。 a“0” or a “1”constitutes a basic code,called bit。 Bit is transliteration of English word bit。Bit is consists of binary and digit,the meaning of bit is binary figure,bit is the smallest unit of digital binary,Sometimes use a bit to show,namely one unit of binary .bit is a existing state,represents turn on or turn off, true or false,up or down,in or out ,black or white。 To be practical,think bit as 1 or 0, form digitized basic factor is bit。 Bit becomes a mark of digitized time。

1.2 particle and pixel

The carrier of film is silver bromide particle, after developing the generated particle is the smallest unit of forming negative image。Particle is constitute of many atoms and molecule。

Assume that there are a quantity of lines in a horizontal direction on digital imagine screen ,and in the vertical direction as well,the the crossing point is a pixel， the pixel on the whole screen is made up of number of rows times Number of column ;the carrier of digital picture is pixel，pixel is the smallest unit of forming digital picture, the more number of rows and number of columns in imager ,the more of pixel in imager, for example,the digital camera with 3 million pixels as we usually said,it has 2048*1536=3145728 pixels

1.3 Degree of blackness and gray-scale

In the method of film photo,the film has been exposure 、developing 、fixing,the particle on the film is restored into black bankenkonsortium ,the more exposure,the more black the negative will be ,the degree of negative color is called degree of blackness in film take photo method。

In the digital picture，endow certain brightness value on pixel, suppose that set the all black value is 0,all white value is set to 255,then the gray of between any of  black and white is full in between these,this is the arrange model with 8 bit，so called 8 bit gray-scale,black-scale usually use bit to show,such as 8 bit (28bit=256bit) ,10 bit(210bit=1024bit) gray-scale,the more the bit ,the more abundant the luminance level,the better of showing effect after dealing ,but the more capacity the computer will need,fortunately computer with big capacity is no longer a problem。

1.4 negative and picture

The same as film developing technology to realize negative come true,computer picture gathering technique and picture dealing make picture come true。

Atom is the basic particle of forming material ,but the bit is not a material, objective existence is a combination of digit，to bring into play human’s imagination，temporarily image bit as “virtual atom”。Under the ray film photographic detection,the basic material of forming negative image is silver particle after silver bromide atom developing ,the generated picture is analog image，It Can not be identified by computer；under ray digitized detection technique,the basic element of forming digital picture is pixel ,the picture generated by it is digitized imagine,very easy to be identified by computer，so apply to computer imagine processing technique, it can produce digital image that compare to photographic film ，ray digital real time imaging detecting technique is new nondestructive detecting technology based on computer image processing technique。

2  ray digitized real time imagining detecting technique basic principle

X ray digitized real time imaging nondestructive detection principle can be summarized by two “switch”,:after X ray penetrate metal material and received by image collector,the image collector transform invisible X ray detecting signal into optical image ,called “photovoltaic conversion”;the image collector ( for image what doesn’t equipped with image intensifier with digital collection function ,using high definition television camera to take in optical image and input computer so as to convert A/D),transform digital signal into digital image，after computer processing ,and restore on the display screen,then it can display defect properties、size、position of inner material 。According to relevant standard to assess flaw level on detecting result so as to up to achieve the goal of nondestructive test 。X ray digitized real time imaging technique is always better than photographic negative no matter in detecting efficiency、 economic benefits、expressive force、teletransmission、and convenient practical usage .so it has gorgeous developing future。

What is called “real time” is means image collecting speed mode，imagine collecting speed can up to 25frames /s (PAL)or 30frames/s(NTSC),namely real time imaging。In regard to image collecting mode,China adopts PAL mode , other countries often adopt NTSC mode。

3 imager way 

The pictures on the image imager is analog image after X ray penetrates workpieces ,analog image just can be identified by computer after transformed into digital image,therefore, the key of analog image transforms into digital image is imaging technique，at present ,imager has three methods,the way of imaging technique is relevant to the form of image imager。

3.1 image intensifier

Ray penetrates workpieces ,the front fluorescent screen of image intensifier,after “photovoltaic conversion”, photoelectron in closed cavity with very high vacuum degree and being high voltage electric field gathering，the analog image of workpiece been absorbed by camera,input computer to do transformation of analog quantity and digitization。

"Calibri" >expressive force、teletransmission、and convenient practical usage .so it has gorgeous developing future。

 What is called “real time” is means image collecting speed mode，imagine collecting speed can up to 25frames /s (PAL)or 30frames/s(NTSC),namely real time imaging。In regard to image collecting mode,China adopts PAL mode , other countries often adopt NTSC mode。

3.2 line array detector

Scanning way of Line array detector is line type scanning，scanning image is a straight line ,many straight lines are aligned to form a image。Workpiece is mobile when detecting，and pass relatively fixed line array detector scanning to get a continuous picture.its working principle is : fluorescent screen accepts x ray energy that penetrate detected object and a visible light can be seen ，the photosensitive diode been shone by visible light and produce voltage signal ，the signal will become 14 (or 16) digital signal and send to computer after dealing by integrated circuit。Adjusting irradiation angle ,repeating the process above，at the end of scanning ,the computer will calculate on database each time get，rebuild needed image,and analyze 。

Scanning way of Planar array detector:(1)line by line scan,and form planar picture output on the planar array detector;(2) surface scan,forming planar image output 

On the planar array detector;detecting workpiece movement,and passing relatively fixed planar array detector to get detecting pictures。

3.4 comparison on three kinds of imaging ways

1) The price of Picture intensifier is low，it can be real time image detected，but imaging sensitivity is not as good as array detecting imaging detector; the volume and weight of picture intensifier are under certain restriction。

2) Planar array imaging plate is high price，imaging sensitivity is relatively high，but imaging is slow，it looks like taking an X ray when using it actually，but take an x ray is just need 3-10seconds，imaging plate can combined with portable high frequency X ray machine with constant voltage 、laptop and so on into a portable X ray imaging system，satisfying use requirement at the scene。

3) Linear sweep machine with low speed of imaging , The price is between picture intensifier and imaging panel, having high requirements on mechanical drive,and detecting speed is low.

4.collecting ways of pictures

Picture collecting is mainly transform light into electric charge by using digital photosensitive element,,transform into digital signal by analog /digital converter chip ,At present ,there are two ways to collect picture:one is used widely CCD element;another is CMOS element。

4.1 CCD camera

CCD is abbreviation of Charge Coupled Device,it is a semiconductor imaging device so it has high sensitivity 、anti hard light 、little distortion、small volume、long life、anti-vibration and other advantages。

Working mode of CCD camera: the picture of being shot object is focused on CCD chip by camera lens,CCD according to the strength of the light accumulate corresponding proportion electric charge,the electric charge accumulated by each pixel is under the control of video sequence ，gradually move to outside,being  filtering magnifying dealing ,forming video signal output,video signal connects to the video input terminal of monitor or television and then the same video image as original image can be seen  。

4.2 CMOS digital imager

CMOS(Complementary metal-oxide semiconductor) ,as CCD,is a semiconductor that can record change of ray of light,the production technology of CMOS is the same as normal computer chip,mainly take advantage of semiconductor that made of silicon and germanium,and make it coexists with ,N and P level semiconductor on the CMOS,electricity produced by these two complementary effect can be recorded and read to video by processing chips.however, disadvantages of CMOS is easy to show  miscellaneous points ,this is mainly due to frequent electricity change and generates superheat phenomena。

4.3comparison

Under the same resolution ,the price of CMOS is lower than CCD, but the picture quality and speed produced by CMOS is lower than CCD。

5  x ray machine

Basic requirements on x ray machine:

1) Focus:for picture intensifier and imaging panel imager,it’s better to adopts small focus,for line array detector,the focus can be big;

2) Frequency :power frequency or frequency conversion (intermediate frequency or high frequency) ,suggest to adopt frequency conversion

3) Voltage and electricity :depend on the thickness of workpiece,choose rated tube voltage and tube current

4) High voltage stability:suggest to adopt constant voltage

5) Ray tube:suggest to adopt metal ceramic pavilion and adopt  forced cooling way so as to work for more hours continuously;

6) Mobile ways:depend on working style,fixed type、mobile type are fine;

7) Bundle of Rays :depend on different working style, orientation or circumferential are fine；

8) Others:depend on workpiece and working style

Computer and procedure

Computer configuration:high configuration computer and laptop sold on the market are okay,better choose industry control machine when under inferior working environment;

Procedure: 1.computer operating procedure,such as Windows XP 2.picture collecting procedure，3.picture handling procedure 4.picture auxiliary assessment program 

7. Picture quality

X ray digital real time imaging picture quality index is the same as photo negative film ,it is penetrameter sensitivity, using penetrameter to describe quality of picture ,it is affected by two factors: 1. Image resolution --using resolution to testing chart to test image resolution description (or definition)  2. Contrast ratio--using gray level difference to describe。

8  the quality of system

X ray real time imaging detecting system (device system) quality index is according to standard regulation or technological conditions in the contrast to stipulate ,using system resolution to describe；system resolution uses resolution testing chart do direct test on system。 

9  imaging technology features

X ray real time imaging detecting technique/technology and films photos detecting technology have same features on technology,films photo detecting technique/technology can basically guide X ray real time imaging detecting technology/technology ,but the both are different on imaging principle and detecting result carrier,so the X ray real time imaging detecting technique/technology has  its own special consideration。

Due to imager is a fixed mechanism , it is impossible to be soft like film ,there is no way to contact the surface of detected workpiece，there must be a distance between imager workpiece surface, from the principle of geometric projection can know that detecting picture must be amplified。In addition,the size and dimensions of pixel is actually bigger than film grain ,to improve sensitivity and definition of picture ,the detecting picture is need to be amplified too,this is the feature of X ray real time imaging detecting technique,Detecting pictures are saved in the computer, and can be transferred to CD and other preservative media。The pictures on the screen can be showed by positive way or negative way ,they are also can be showed by black way or colorful way。

10 detecting equipment。

“ We must polish our tools so as to be easy and efficient to do our work ”。According to detecting object(workpiece) design and produce equipment, according to Different detecting orientation ,detecting equipment at least equipped with a free degree;for detecting equipment has higher running precision ,a equipment usually has 1～3 free degree; merely free degree is more,the cost of equipment production costs is high,equipment design and production level are always affect workpiece detecting quality and speed 。

11 standard 

Regarding to X ray real time imaging detecting methods, up to now our country has issued GB 17925-1999 《gas cylinder butt weld X ray real time imaging detection 》 and GB/T 19293-2003 《butt weld X ray real time imaging detecting methods》GB/T 19293-2003 is the standard about butt weld X ray real time imaging detecting ,GB 17925-1999 is a standard regarding to gas cylinder products butt weld X ray real time imaging detecting methods 。 These two standards released,marking our country X ray real time imaging nondestructive detecting technique has up to a new level,however,ray real time imaging nondestructive detecting standardization system has not built in our country，so we need to as soon as possible build our ray real time imaging nondestructive detecting standardization system。

12   application of X ray digital real time imaging technique 

X ray digitized real time imaging technique has been widely applied to every area in industry ,such as nondestructive on gas cylinder、boiler、pressure vessel、pressure tube、butt weld of oil and gas transmission pipe，automobile wheel hub、 automobile / aircraft tyre and so on ,mechanical accessories nondestructive。

12.1 gas cylinder butt weld X ray real time imaging detection

In the middle 1990s,X ray digitized real time imaging detecting has been officially applied to liquefied petroleum gas cylinder butt weld nondestructive detection。

1- X ray tube focus   2- gas cylinder  3- detected weld  4-picture intensifier  5-optical pixel  6-camera

picture collector mainly adopts picture intensifier technique ,namely the first generation technique of X ray real time imaging detecting system，based on this technique forming 17925-1999 standard。The equipment with this technique is low cost Although picture quality is lower than present line array detector technique，but passing decades of years actual application， proving the technique has been grown up and satisfying requirements of gas cylinder and pressure tube as well as relate to pressure vessel weld nondestructive 。So far it is still powerful 。Detecting  equipment is constituted of two free ， when detecting circumferential weld, axis of rotation on the gas cylinder shows 360 degree rotation，when detecting longitudinal weld ,gas cylinder will move along the horizontal direction, make sure detection on weld。

12.2  line array detector X ray real time imaging detecting technique

Line array detector X ray real time imaging detecting technique is present more popular X ray real time imaging detecting technique,it adopts line array detector as picture collector，it can be said the second generation X ray real time imaging detecting system technique。Due to line array detector itself has digitized collecting function，therefore optical lens、camera、and picture collecting card can be saved;although line array detector is more expensive than picture intensifier，but due to line array detector is adopts line scanning gradually imaging ， for X ray  source,it doesn’t emphasize adopt small focus,simultaneously save optical lens、camera and picture collecting card，therefore the whole cost is not more expensive than picture intensifier imaging system，Detecting quality of picture is better than picture intensifier，on the basis of this ,build standard of GB/T 19293-2003 《butt weld X ray real time imaging detecting method》   

Line array detector X ray real time imaging detecting technique has been widely applied to  gas cylinder 、boiler、pressure vessel 、pressure pipe、 oil and gas transmission pipe butt weld as well as mechanical accessories 、aerospace parts and so on areas

12.3 plane array detector X ray real time imaging detecting technique

Plane array detector can be thought as gather of multiple lines array detector;having larger capacity pixel，picture sensitivity is high ，high resolution and high definition，representing the latest technique of present picture collector, namely third generation X ray real time imaging detecting system ,but the production of plane array detector is mainly concentrate on few manufacturers in our country， forming technological monopoly,the price is high,at present ,it is mainly used for research project in laboratory,and not used for actual application ， believing in the nearly future，it must be widely used 。

13  conclusion 

Ray digital real time imaging technique as a emerging nondestructive detecting technique has very wide prospects, at the time of digital era coming , let’s hug ray digital real time imaging nondestructive detecting new technique like hugging the morning sun。