e. If a magnet was used to remove fine magnetic particles from suspension in the centrifuge tube, the
suspension SHALL be demagnetized prior to being poured back into the magnetic particle machine.
f. The inside of the centrifuge tube SHALL be cleaned to eliminate any residual fluorescence remaining
after each use.
Figure 3-34. Drawing Fine Magnetic Particles from Vehicle with Horseshoe Magnet
The removal of surface oil and grease becomes very important in the cleaning of part prior to wet fluorescent magnetic
particle inspection. Most petroleum distillates, lubricating oils, and greases fluoresce. Such materials must be kept out
of the testing bath because of the increase in background fluorescence that they produce.
Application of Suspension.
Application of the suspension using fluorescent magnetic particles is identical with the procedure described in detail for
the wet visible method.
Blacklight Information (See Penetrant Chapter).
Ambient Light Requirements.
Inspection booths of a stationary fluorescent magnetic particle system SHALL NOT exceed 2 lumens per square foot
(lm/ft2; 1 lumen per square foot equals 1 foot-candle) of ambient light. For portable applications it is not always
possible to achieve ambient light levels as low as this. As the ambient light level is increased, the intensity of black
light must also be increased. When performing portable fluorescent magnetic particle inspections, a dark colored
canvas or photographers black cloth SHALL be used to darken the area of interest to the lowest possible ambient light
levels during the inspection.
The measurement of visible light intensity is easily accomplished by using solid-state photometers. Measurements of
visible light are keyed to the response of the visual system of a standard human observer. The unit of energy for visible
light is the lumen-hour and represents the amount of energy in the visible light spectrum distributed in a specific way
that is related to the response of the standard human eye. The energy flux, that is the energy per unit of time, then is