3
Design and Function
26/198 CCD CAM 100 – Installation and Operating Manual
3.5 Function
Measuring range
Material
Illumination
Video curve
Bright
level
Dark
level
Bright/dark
transition
(edge 1)
Dark/bright
transition
(edge 2)
Fig.8: Function principle (transmitted light method)
With the transmitted light method, the web of material is radiated
from an external illumination (light box) that is arranged behind
the web as viewed from the CCD camera.
The light sensitive elements of the CCD line sensor of the camera
convert the incident light into electric voltage. Contrast transitions
(bright/dark, dark/bright) that result from the partial covering of
the illumination with the web of material lead to changes in the
voltage. The voltage level determined from the light-sensitive
elements are shown in the display of the CCD camera as a video
curve.
The CCD camera can detect several contrast transitions in its
measuring range. In doing so, the zoom lens of the camera must
be set in such a manner that all contrast transitions that should be
detected are located within the measuring range. The contrast
transitions can be caused by one or several webs of material.
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