B5WC Built- In Color Sensor User's Manual ( E612- E1- 01) 10
■If the sensing object is a liquid
So far, we have described the case where the sensor's light is irradiated on the surface of the sensing
object as a general reflective optical sensor, but it can also be used to distinguish differences in the color
of liquids in transparent containers. Example schematic diagrams are shown below. As in the diagram,
install a reflector on the opposite side of the color sensor and place a transparent container containing the
liquid to be detected between them. It is difficult to judge the color of the liquid by irradiating light directly
on the surface of the liquid in the container from a color sensor.
The following chart shows the results (informative) of liquid color measurements using the above
measurement method.
As an example here, a liquid reagent with known color information called ASTM color is used.
With this measurement method, the color of a liquid in a transparent container can be detected by the color
sensor as received RGB light intensity. In this case, however, the RGB output values of the color sensor
will vary depending on the installation environment, mainly as described below.
Condition (1) Container size
As shown in the receiver output - sensing distance characteristics of the color sensor, the receiver output
also fluctuates when the "container size"(i.e. "distance between the sensor and the reflector") changes.
In particular, if the distance is too close (approx. 0 to 20mm) or too far (approx. 50mm or more), it will be
difficult to ensure the receiver output. It is recommended that the distance between the sensor and the
reflector be within the range of 20 to 50mm.
Condition (2) Reflector material and surface condition
Select the reflector with as uniform a surface condition as possible. For reference, OMRON uses a
reflector of "SUS430/surface polished (#240 or #320 equivalent)" in its measurements.
Thus, the RGB output values of the color sensor will fluctuate when either of the above conditions (1) or
(2) is changed. Since these conditions vary depending on the customer's application, it is ideal in actual
use to conduct a thorough evaluation to determine the optimal combination that will produce the desired
RGB output values.
Example of liquid color measurement
RGB output voltage ratio to petroleum product color standard sample*
dia.=7 mm
Reflective plate: Stainless steel 430
Detected object: ASTM reagent
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