When the coil is used to establish a longitudinal Magnetic field within the part is placed on the inside surface of the coil. Just as done with a head shot, the bath is then flowed over the surface of the part. A magnetizing current is applied to the part for a short duration, typically 0.5 to 1.5 seconds, just after coverage with the bath is interrupted. (Precautions should be taken to prevent burning or overheating of the part) Leakage fields from defects attract the particles to form visible indications.
Theoretical horizontal unit can also be used to establish a circular magnetic field using a central conductor. This type of a setup is used to inspect parts that have an open centre, such as gears, tubes, and other ring - shaped objects. A central conductor is an electrically conductive bar that is usually made of copper or aluminium. The bar is inserted through the opening and the bar is then clamped between the contact pads When current is passed through the central conductor, a circular magnetic field flows around the bar and enters into the part or parts being inspected.