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Tuesday, 8 November 2016

MAGNETIZING CURRENT IN MAGNETIC PARTICLE INSPECTION.

Half wave Alternative current (HWAC):- When single phase alternative current is passed through a rectifier, current is allowed to flow in only one direction. The reverse half of each cycle is blocked outsourcing that a one directional, pulsating current is produced. The current rises from zero to a maximum and then returns to zero. No current flows during the time when the reverse cycle is blocked out. The HAWC repeat at same rate as the unrectified current (60hertz typical). Since half of the current is blocked out, the amperage is halftone the unaltered AC.
This type of current is often referred to as half wave Dc or pulsating DC. The pulsation of the HWAC helps magnetic particle inspection form by vibrating the particles and giving them added mobility. This added mobility is especially important when using dry particles. The pulsation is reported to significantly improve inspection sensitivity. HAWC IS most often used to power Electromagnetic yokes.
Full Wave Rectified Alternating Current (FWAC):-Full wave rectification inverts the negative current to positive current rather than blocking it out. This produces a pulsating DC with no interval between the pulses. Filtering is usually performed to soften the sharp polarity switching in the rectified current. While particle mobility is not as good as half - wave AC due to the reduction in pulsation, the depth of the subsurface magnetic field is improved.
Three Phase Full Wave Rectified Alternating Current :- Three phase current is often used to power industrial equipment because it has more favorable power transmission and line loading characteristics. These type of electrical current is also highly desirable for magnetic particle testing because when it is rectified and filtered, the resulting current very closely resembles direct current.