Bolt tshuaj xyuas yog dav categorized rau hauv ob txoj kev: phau ntawv thiab automated. Cov txheej txheem phau ntawv yog ib txwm siv ntau tshaj plaws thiab siv dav rau kev txheeb xyuas qhov sib xws. Txhawm rau txo qhov kev tso tawm ntawm cov khoom tsis zoo, cov neeg ua haujlwm tsim khoom feem ntau ua qhov kev kuaj pom ntawm cov khoom ua ntej ntim lossis xa khoom xa tuaj, txhawm rau txheeb xyuas thiab cais cov khoom tsis raug (tsis xws li xov puas, cov khoom sib xyaw tsis raug, xeb, thiab lwm yam).
Lwm txoj hauv kev yog kev siv lub tshuab kuaj xyuas tag nrho, feem ntau yog siv cov khoom sib nqus sib nqus. Cov txheej txheem no leverages kev sib cuam tshuam ntawm magnetic particles thiab magnetic flux to generated ntawm bolt defects. Nws siv qhov sib txawv ntawm qhov sib nqus permeability ntawm qhov tsis xws luag -xws li cov kab nrib pleb, slag inclusions, lossis cov khoom sib xyaw ua yuam kev- thiab cov hlau nyob ib puag ncig. Thaum lub bolt yog magnetized, lub magnetic teb ntawm cov khoom discontinuities yuav distorted; Qhov no distortion ua rau ib feem ntawm cov magnetic flux tawm mus rau lub workpiece nto, yog li attracting magnetic hais. Qhov kev nyiam no ua rau muaj qhov sib txuam ntawm cov khoom ntawm qhov chaw tsis zoo-paub tias yog "magnetic indication"- uas, nyob rau hauv cov teeb pom kev zoo, qhia qhov tseeb qhov chaw thiab geometry ntawm qhov tsis xws luag. Los ntawm kev soj ntsuam thiab txhais cov khoom sib xyaw ua ke no, lub hom phiaj ntawm kev txheeb xyuas thiab tshem tawm cov khoom puas tau tiav.