Yokes

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Yokes are the power tools for Magnetic Particle Inspection. These handheld electromagnets create a magnetic field in a Steel (Ferrous) work piece.

Particle Mobility, are the forces that effect the movement of Magnetic Particles on the surface of the work piece. The higher the Particle Mobility the faster, and more reliable, the particle will congregate to a defect or a change in surface profile. Let us outline the fields produced by Yokes to help you understand the right Yoke for you.

AC Yokes: These fields provide the greatest particle mobility as the frequency of the power simply causes the Particle to vibrate. The polarity at each pole (leg) alternates from positive to negative at the same frequency as the electrical input current of 50 to 60 Hertz (pulses per second).

AC / DC Yokes: The fields provide is identical to those outlined above. The DC Portion from Yokes is a Phase Controlled pulse or rectified AC. The inductance of the Yoke’s Coil and Iron Core is enough that the Field induced into the material is Straight DC, with a slight ‘ripple’ due to the AC input frequency of 50 or 60 Hertz.

Battery Operated Yokes: These yokes take the 12 Volts DC from the Battery and Chops the current, simply turning the field on and off at 125Hz. This Chopping of the electrical supply lowers the effective draw on the battery, thus extending the useful life of a charge. As the chopped current keeps re-energizing the coil, the flat level of the DC curve is interrupted creating a ripple effect that induces some particle mobility

Permanent Magnets: These yokes simply induce a magnetic field into the work piece, almost the equivalent of a full wave DC field. As a result there is no change in the strength or polarity (frequency) of the field, thus there is very low Particle Mobility.

To summarize the Particle Mobility of Magnetic Fields induced by Yokes, our AC Yokes provide the best Particle Mobility, with AC/DC Yokes being second best, next is the Battery Operated Yokes with Permanent Magnet Yokes last. However, let us be mindful that a DC Field will highlight both surface and subsurface defects while AC only highlights surface indications. So in conclusion, a DC Field with a more pronounced collapse, between pulses, would be beneficial for increased Particle Mobility. We have a Yoke to address various needs of any operator.