An object beyond the cutoff distance, either stationary (and when positioned as shown in

Figure 5 on page 4), or moving past

the face of the sensor in a direction perpendicular to the sensing axis, may cause unwanted triggering of the sensor if more light is

reflected to the near detector than to the far detector. Correct the problem by rotating the sensor 90° (

Figure 6 on page 4). The

object then reflects the R1 and R2 fields equally, resulting in no false triggering. A better solution, if possible, may be to reposition

the object or the sensor.

E = Emitter

R1 = Near Detector

R2 = Far Detector

R2

R1

E

Fixed

Sensing

Field

Strong

Direct

Reflection

to R1

Core of

Emitted

Beam

Cutoff

Distance

Reflective

Background

T30FF

Figure 3. Reflective Background - Problem

E = Emitter

R1 = Near Detector

R2 = Far Detector

R2

R1

E

Fixed Sensing Field

Strong Direct

Reflection

Away

From Sensor

Core of

Emitted

Beam

Cutoff

Distance

Reflective

Background

T30FF

Figure 4. Reflective Background - Solution

Fixed

Sensing

Field

Cutoff

Distance

R1 = Near Detector

R2 = Far Detector

E = Emitter

T30FF

R1

E

R2

Reflective

Background

or

Moving Object

A reflective background object in this position or moving across the sensor

face in this axis and direction may cause a false sensor response.

Figure 5. Object Beyond Cutoff - Problem

E

= Emitter

R2 = Far Detector

R1 = Near Detector

T30FF

E, R2, R1

Fixed

Sensing

Field

Cutoff

Distance

Reflective

Background

or

Moving Object

A reflective background object in this position or moving across the sensor

face in this axis is ignored.

Figure 6. Object Beyond Cutoff - Solution

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 is slightly shorter than for higher reflectance targets.

This behavior is known as color sensitivity.

For example, an excess gain of 1 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 130 mm (5.1 in)

cutoff model, for example; and 130 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.

T30AD9 NAMUR Series Fixed-Field Sensor

4

www.bannerengineering.com - Tel: +1-763-544-3164

P/N 41685 Rev. F