Civil Engineering Reference
In-Depth Information
for a smaller surface
Enhance internal stresses
and strains
Cross-
polarization
Place two sheets of linear polarizer at 90° to each
other, one on each side of the transparent product to
be inspected; detect changes in color or pattern with
defects
Enhance thickness changes Cross-
polarization
Use in combination with dichroic materials
Diffuse reflection Reduce contrast of brightness patterns by reflecting a
white diffuse surface on a flat specular product;
produces an iridescent rainbow of colors that will be
caused by defects in a thin transparent coating
Moiré patterns
See “Enhance surface projections or indentations”
above
Enhance nonspecular
defects in a specular
surface, such as a mar on a
product
Polarized light
A specular non-metallic surface acts, under certain
conditions, like a horizontal polarizer and reflects
light; non-specular portions such as a mar will
depolarize it; project a horizontally polarized light at
an angle of 35° to the horizontal
Desired
Enhancement in
Inspection Task
Special-Purpose
Lighting or Other
Aids
Technique
Enhance opacity
lights changes
Transillumination
For transparent products, such as bottles, adjust to
give uniform lighting to the entire surface; use
opalized glass as a diffuser over fluorescent tubes
for sheet inspection; double transmission
transillumination can also be used
Enhance color
changes, as in color
matching in textiles
Spectrum-balanced
lights
Choose lighting type to match the spectrum of
lighting conditions expected when the product is
used; use 3000 K lights if the product is used
indoors, 7000 K lights if it is used outdoors
Negative filters, as in
inspecting layers of
color film for defects
These filters transmit light mainly from the end of
the spectrum opposite to that from which the
product ordinarily transmits or reflects; this reversal
makes the product surface appear dark, except for
blemishes of a different hue, which are then brighter
and more apparent
Enhance fluorescing
defects
Black light
Use ultraviolet light to detect cutting oils and other
impurities; may be used in clothing industry for
pattern marking; fluorescing ink is invisible under
white light, but very visible under black light
Enhance hairline of
breaks in castings
Use of ultraviolet light inspection will detect pools
of oil in the cracks
Adapted from Eastman Kodak Co. (1983), with permission.
Coat with fluorescing
oils
