Delta CS24D User Manual download pdf (Page 31)

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.

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Delta CS24D User Manual Page 31

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