Delta CS24D - Manual (Page 31)

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closest to the sensor is 3/4 by 2 1/2 inches and tapers down to about 1/2 x 1 inches.
(Figures 1 and 3 show the critical sensing and light areas).
Q. Can I use the CS24D pointing up?
A. The CS24D can be mounted in any orientation. With the sensor pointing up, it is
important to watch dust build-up on the sensing window. Also sunlight should not be
allowed to enter directly into the sensor window.
Q. How often should the CS24D be re-taught?
A. As with all similar sensors, re-teaching is required periodically. The CS24D has
compensation to greatly reduce the time and temperature drift inherent with the LEDs.
The required frequency of Teaching depends on the required precision, and could be as
often as once a week, or as infrequent as once a quarter or more.
Q. What are the limitations to the detection of colors?
A. The measurement consistency varies from application to application. Here is a list of
some of the error sources associated with any color sensor, including the CS24D.
Sample color variations: Often colors vary from sample to sample. Dark objects tend to
display the largest amount of variations. If possible, check multiple samples over time to
verify consistency before setting up the thresholds. The ability to Teach the CS24D with
eight readings per output can greatly improve performance with sample variations.
Presentation variations: The largest variation in multiple readings of the same object is
typically differences in the orientation of the object to the sensor. Not only does the
distance from the object to the sensor affect the readings, but so does the angle of the
object. The least sensitive objects are those with a matte or other non-glossy finish and
with a flat to slightly convex surface. The most difficult objects have a gloss finish and a
concave surface. The CS24D handles these types of variation better than most color
sensors, in fact spectrophotometers often require contact measurements which eliminate
distance variations but also make them unsuitable for most on-line applications. Small
sensor-to-object variations (~1/8") typically can be handled. The ability to Teach the
CS24D with eight readings per output can significantly help performance with
presentation variations.
Environment: Dust collecting on the CS24D's window reduces signal strength. Use of
ratios eliminates errors from uniformly distributed dust, but eventually the loss of signal
strength will impact performance.
Noise: Electrical and optical noise is typically the next largest variation from reading-to-
reading of the same object. Noise is greater for green and blue since the green and blue
LEDs are less intense, and less for the Intensity and red values. Optical noise is primarily
caused by changing ambient light conditions. Extraneous light in the sensing area is an
error signal and should be eliminated as much as possible. Moderate levels of ambient
light may be tolerable, while sunlight is almost never tolerable. If response time
requirements allow it, most noise can be effectively eliminated in many applications
simply by increasing the averaging (using Delta’s ColorSense setup program) to as high
as the allowed by the application’s response time requirements.
Temperature: The intensity of all LEDs diminished as temperature is increased. This
effect is compensated for in the CS24D. The LED color also drifts slightly with
temperature, but this is insignificant in most applications.