tailieunhanh - Volume 17 - Nondestructive Evaluation and Quality Control Part 13

Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | suited to specific applications. The vidicons offer the highest frame rates in formats of 10242 and more the line scanners have excellent resolution at moderate prices and the micro-densitometers are the most precise with regard to photometric and geometric quantities. Most microdensitometers will digitize to 12 bits which limits their dynamic range to about in film density. As noted in Table 2 the standard scanning microdensitometer row one will take longer up to several hours to scan film if the film density is over 2. The laser scanners are faster depending on the make because of the more intense laser light source and the fact that one axis is scanned with the light beam rather than mechanically. Table 2 Typical characteristics of image digitization devices Type Image quality Pixel size or pixel number resolution Acquisition time per 10242 by 8-bit image Interscene dynamic range Image area mm X mm in. X in. Face plate illumination lx ftc Point source and detector Microdensitometer Excellent 5-75 Pm 200 p in. a 15 min 4096 500 X 500 20 X 20 . . Laser scanner Excellent 35 or 75 m or in. 1 min 4096 430 X 350 17 X 14 . . Linear detector Linear CCD array Good 4096 500 ms 1500 . . . Photodiode array Good 1024 5 s 1000 . . . Solid-state cameras CCD Fair 1320 X 1035 140 ms 500 . CID Fair 776 X 512 33 ms b 200 . Tube type cameras vidicon family Vidicon Sb2S3 Fair 1500 33 ms lag 20 80-200 . 5 Newvicon ZnSe Fair 800 33 ms lag 10-20 50-200 . Pasecon Chalnicon CdSe Fair 1600 33 ms lag 510 30-60 . 1 Saticon Se Te As Fair 1200 33 ms lag 3 50-160 . 6 Plumbicon PbO Fair 1200 33 ms lag 4 80-160 . SIT Silicon Fair 750 33 ms lag 7 60 . a Aperture. b 776 X 512 Linear CCD or photodiode arrays are good choices for film digitization and can have even better dynamic ranges than those listed in Table 2. When these devices are cooled each 7 C 13 F reduction in temperature reduces the root mean .