FED-STD-228A
4.1.3 When an apparatus with a scale in the eyepiece is used, the ruled glass disc shall be placed in the
ocular and calibrated. The specimen shall be placed on the state so as to expose the full thickness of the
insulation. The microscope shall be focused on the specimen and the thickness of the insulation
determined by counting the divisions of the ruled disc in the eyepiece which cover the distance from the
inner edge to the outer edge of the insulation and the value recorded.
4.1.4 One set of measurements on each specimen shall be made. Each set of measurements shall
consist of the maximum and minimum thickness.
4.2 Minimum thickness.
4.2.1 The inspection unit shall be examined for thin places in the insulation. A specimen shall be cut
perpendicular to the axis of the wire or cable so as to expose for measurement the point where the
insulation is considered the thinnest. The thickness of the thinnest point of the insulation shall then be
measured as described in 4.1.
4.2.2 If no thinnest point is located in the insulation of the inspection unit, the procedure shall be as
described in 4.1.
5. RESULTS
5.1 Average thickness.
5.1.1 Unless otherwise specified in the detail specification, five specimens from each inspection unit shall
be tested.
5.1.2 The average thickness of the insulation of the inspection unit shall be the average of the results
obtained from the specimens tested.
5.2 Minimum thickness.
5.2.1 If a thinnest point is found in the insulation of the inspection unit, 4.2, the minimum thickness of the
insulation of the inspection unit shall be the thickness of the insulation obtained at that point.
5.2.2 If no thinnest point is found in the insulation of the inspection unit, 4.2, the minimum thickness of
the insulation of the inspection unit shall be the smallest of all values averaged in determining the
average thickness, 5.1.2.
5.3 The average thickness and minimum thickness of the insulation of the inspection unit shall be
recorded to the nearest mil of 0.0001 inch.
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