13
3.4 Minimum Clearance to Reflective Surfaces
If reflective surfaces are located within the aperture angle between the emitter and the receiver, reflection
may result which could cause an obstruction to go undetected. For this reason, a minimum clearance m
between reflective objects and the optical axis must be maintained.
Beam angles are taken from the IEC 61496-2 standard. They represent worst case values. Actual values
are lower.
Danger Zone
reflective object
Central Beam
Emitter
Receiver
Light Bundle
Interrupted
m = tan
a
× (Distance Emitter – Receiver)
a
= aperture angle of emitter and receiver optics
a
= ±2,5°
Minimum Clearance m in m
2
4
6
8
10
12
14
16
18
20
0,10
0,20
0,30
0,40
0,50
0,60
0,70
0,80
0,90
0,131
Range in m
