Manual

P/N 121516 3
Q40 Sensors – dc-Voltage Series
Banner Engineering Corp. • Minneapolis, MN U.S.A.
www.bannerengineering.com • Tel: [phone]
Color Sensitivity
The effects of object reflectivity on cutoff distance, though small, may be important for
some applications. It is expected that at any given cutoff setting, the actual cutoff distance
for lower reflectance targets will be slightly shorter than for higher reflectance targets (see
Figure-of-Merit information on page 5). This behavior is known as color sensitivity.
For example, an excess gain of 1 (see page 5) for an object that reflects 1/10 as much light
as the 90% white card is represented by the horizontal graph line at excess gain = 10. An
object of this reflectivity results in a far limit cutoff of approximately 190 mm (7.5") for the
200 mm cutoff model for example; thus 190 mm represents the cutoff for this sensor and
target.
These excess gain curves were generated using a white test card of 90% reflectance.
Objects with reflectivity of less than 90% reflect less light back to the sensor, and thus
require proportionately more excess gain in order to be sensed with the same reliability as
more reflective objects. When sensing an object of very low reflectivity, it may be especially
important to sense it at or near the distance of maximum excess gain.
E
R2
R1
Q40 sensor
E = Emitter
R1 = Near Detector
R2 = Far Detector
Fixed Sensing Field
Strong
Direct
Reflection
to R1
Core of
Emitted
Beam
Cutoff
Distance
Reflective
Background
E = Emitter
R1 = Near Detector
R2 = Far Detector
Reflective
Background
or
Moving Object
E
R2
R1
Q40 sensor
Fixed
Sensing
Field
Cutoff
Distance
Figure 3. Reflective background – problem Figure 4. Reflective background – solution
Figure 5. Object beyond cutoff – problem Figure 6. Object beyond cutoff – solution
E = Emitter
R2 = Far Detector
R1 = Near Detector
E, R2, R1
Q40 sensor
Fixed
Sensing
Field
Cutoff
Distance
Reflective
Background
or
Moving Object
E
R2
R1
Q40 sensor
E = Emitter
R1 = Near Detector
R2 = Far Detector
Fixed Sensing Field
Strong Direct
Reflection
Away
From Sensor
Core of
Emitted
Beam
Cutoff
Distance
Reflective
Background
A reflective background object in this position or
moving across the sensor face in this axis and
direction may cause false sensor response.
A reflective background object in this position or
moving across the sensor face in this axis will be
ignored.