Delta CS64A - Manual (Page 14)

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7.2 Edge Effects
The CS64A-00 sees an area of about 0.35 x 0.35 inches. When material is entering or
leaving the sensing area, the color can appear wrong for a variety of static and dynamic
conditions. For best results, read the analog outputs and compute the color only when the
CS64A sees the intended material over the entire viewing area.
7.3 Angle of CS64A to Material
The most consistent readings are obtained if the material is perpendicular to the CS64A
in both planes. If angle differences cannot be avoided, it is preferable to have the angle
the narrow way and the standoff at the longer end of the recommended range (2 inches
for CS64A-00). In some cases when dealing with shiny materials, angling the sensor
slightly with respect to the target may produce more consistent readings. Concave
surfaces should be avoided if possible.
7.4 Distance Performance
The amplitudes of the signals reach the maximum value close to the CS64A (about 1.5"
for CS64A-00) and then decrease with distance. The ratios of Red/NIR, Green/NIR and
Blue/NIR are adjusted to be constant within the specified tolerance over the specified
working range of the sensor. As the sample is moved further from the CS64A, the ratios
will gradually become less consistent. This effect, along with the decrease in signal
amplitude, limits the usable range of the CS64A. In applications where the differences in
samples are large, the CS64A-00 may work well out to 3" or more.
7.5 General Information
The term "color" actually implies visible light--wavelengths from about 400nm (violet) to
about 750nm (deep red), although in this document any wavelength that can be seen by
the CS64A is referred to as a color.
With high intensity blue LEDs (450nm) and several visible wavelengths up to 700nm
available, DELTA's sensors can be made to see practically the entire visible color
spectrum. But the capability does not stop there; the precision photodiode in the sensors
can see into the near infrared up to about 1,000nm, and LEDs are readily available in this
region as well.
NIR LEDs are used in the CS64A-00 and similar general purpose color sensors to
provide a baseline value that is relatively constant for a given type of material regardless
of color. This "divisor color" compensates for distance variations.
The NIR spectrum can be valuable in special applications. For example, the ratio of two
different NIR colors can be used to detect certain types of glue, while ignoring visible
color variations. Contact Delta for more information on these applications.