3. Operation
3.4.3 Dimensional measurement using a scale
Place the scale on the screen and measure the enlarged image.
Divide the measurements by the magnification of the projection lens to determine the
actual dimensions.
[Example]
Measured value on the screen: 150mm
Projection lens magnification: 10X
150/10=15
Actual dimension of the workpiece: 15mm
Work
ection screen
Scale
Magnified
dimension
y The optional reading scale is ideal for this type of measurement because the graduated
surface of the scale fits on the screen glass, providing parallax-free measurement.
3.4.4 Comparison with an overlay chart
Measurement and inspection are performed by comparing the workpiece image with the
standard overlay chart which is custom-made for the selected magnification. Use this
method for measurement of shapes, multiple points and dimensions.
This method of measurement is suitable for checking a complicated part feature which
cannot be inspected in a simple one-dimensional measurement.
Adding tolerance lines onto the standard overlay chart will improve inspection efficiency,
since workpieces can be inspected with reference to these lines.
Standard charts can be made from the workpiece blue print, or the master workpiece
image projected on the screen. Use transparent or semi-transparent tracing sheets(or
film) to make them. For close inspection or for long-term storage, plastic tracing sheets
are recommended because of their greater dimensional stability.
Tolerance lines
No.99MBA043A 3 - 15
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