Rockwell Automation 5370-CVIM2 Module - Manual (Page 58)

5 Chapter Chapter 3
Image Acquisition Parameters
3–19
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Scale –– When the “ Computed ” calibration mode is selected, this field
will display the computed “scale” value, which is the ratio of the “world
units” dimension (such as inches) of the calibration object to the same
dimension in pixels (the
Nominal or “learned” value). When the
“ Absolute ” calibration mode is selected, you can enter a predetermined
scale value directly into this field.
•
P&P Gage –– The button activates the gage pick and place
function. You can change the length and position of the calibrate gages,
but you cannot rotate them from their X– or Y–axis orientation. For
details about this function, see Chapter 5, Pick and Place Functions.
•
Threshold –– The button accesses the threshold cursors. For
details about this function, see Chapter 8, Thresholds, Filters, and
Morphology.
•
Feature A, Feature B –– The and buttons accesses
the “feature,” or edge selection panels for the respective features.
•
Units –– When you pick this field, a “typewriter” keyboard appears on
the display, on which you can enter the appropriate name of the “world
units” (such as “
Inches ”).
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Done –– When you pick the button, the system exits back to the
Camera setup panel.
Calibrate Mode: Computed Mode vs Absolute Mode
The calibrate function provides two methods of calibration: the Computed
mode, and the Absolute mode.
Computed mode –– The calibrate function defaults to the Computed mode,
which is the appropriate mode when you want the CVIM2 system to compute
the calibration scale on the basis of you choice of “world units” (such as
inches) per pixel. Using this mode, you position the calibration gages and
perform a
Nominal (or “learn”) function to “learn” the calibration object
dimension in pixels, then enter that dimension in world units (such as inches)
to perform the scale computation.
Absolute mode –– The Absolute mode is appropriate when you already
know the scale values; that is, you know that each pixel in the image field
represents n world units (such as inches), or fractions thereof. Using this
mode, you simply enter the scale value, n. The calibration gages are not used.
Figure 3.12 (page 3–20) shows a Calibrate panel with the Computed mode
selected for the X calibration gage and the Absolute mode selected for the Y
calibration gage (normally, both calibration gages would use the same
Cal.Mode selection).