GE XLG3 - Manual (Page 110)

User Manual Chapter 7 Measuring Features and Defects 101
Taking Shadow Measurements
For maximum accuracy in any type of shadow measurement, you begin by positioning the
shadow tip carefully.
To Position the Probe Tip for a Shadow Measurement Image
Before freezing a shadow measurement image, position the probe tip to meet these
criteria:
• Tip-to-target proximity. The tip is as close to the surface as possible while still
viewing the entire item to be measured. The shadow moves toward the left as the tip
approaches. Measurements can be made even if the tip is so close that the image is
somewhat out of focus, as long as the features are sharp enough to place the cursors
accurately.
For depth measurements, in particular, the tip needs to be close enough to noticeably
break the shadow so that the system can accurately differentiate between the raised
and recessed surfaces.
• Perpendicular surface. There are two criteria here. (1) The shadow is straight up
and down, indicating that the surface is vertically perpendicular to the probe view. (2)
Visual cues, such as illumination and perspective, indicate that the surface is
approximately perpendicular to the probe view horizontally as well.
• Shadow’s proximity to item. The shadow is near, and on the same plane as, the
item you want to measure.
Bad Example
• Shadow is on right side of screen.
(Optical tip needs to move closer to surface.)
• Shadow is not quite vertical, and surface appears skew.
(Surface is neither vertically nor horizontally perpendicular to
probe view.)
Note: Linear measurements can be taken on a skew surface, but
only if you select the “skew” measurement type.
Probe
Good Example
• Shadow is further left.
(Optical tip is very close to surface.)
• Shadow is vertical, and surface does not appear skew.
(Surface is perpendicular to probe view.)
• Shadow is on same plane as item to be measured.
Probe
Both images were captured for length
measurement across the slot.