S18 sensors – ac-voltage series, Color sensitivity – Banner S18 Series User Manual

Page 3

P/N 121521

S18 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 (0.08"), 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.

3&&

Core of

Emitted

Beam

#UTOFF

$ISTANCE

2EFLECTIVE

"ACKGROUND

Strong

Direct

Reflection

to R1

&IXED

3ENSING

&IELD

Cutoff

Distance

R1 = Near Detector

R2 = Far Detector

E = Emitter

S18FF

Fixed

Sensing

Field

Reflective

Background

Moving Object

Figure 3. Reflective background – problem

Figure 4. Reflective background – solution

Figure 5. Object beyond cutoff – problem

Figure 6. Object beyond cutoff – solution