Q25 sensors – ac-voltage series, Color sensitivity – Banner Q25 Series User Manual
Page 3
P/N 121517
3
Q25 Sensors – ac-Voltage Series
Banner Engineering Corp.
•
Minneapolis, MN U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
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 20 mm (0.8") for the
25 mm (1") cutoff model for example; thus 20 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.
1&&
%
2
2
2
2
&IXED
3ENSING
&IELD
3TRONG
$IRECT
2EFLECTION
TO
"EAM
#UTOFF
$ISTANCE
2EFLECTIVE
"ACKGROUND
2
2
%
%
2
2
2EFLECTIVE
"ACKGROUND
OR
-OVING
&IXED
3ENSING
&IELD
#UTOFF
$ISTANCE
1&&
Figure 3. Reflective background – problem
Figure 4. Reflective background – solution
Figure 5. Object beyond cutoff – problem
Figure 6. Object beyond cutoff – solution
2
2
2
%
1&&
&IXED
3ENSING
&IELD
#UTOFF
$ISTANCE
2EFLECTIVE
"ACKGROUND
OR
-OVING
%
2
2
1&&
2
2
&IXED
3TRONG
2EFLECTION
!WAY
&ROM
#ORE
%MITTED
"EAM
#UTOFF
$ISTANCE
2EFLECTIVE
"ACKGROUND
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.