Page 175 - Sensors and Control Systems in Manufacturing
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Cha p te r
T h ree
In recent years, visible LEDs have been introduced as light sources
in photoelectric controls. Because the beam is visible to the naked eye,
the principle advantage of visible LEDs is ease of alignment. Visible
beam photoelectric controls usually have lower optical performance
than IR LEDs.
The modes of detection for optical sensors are (1) through-beam
and (2) reflection (diffuse reflection and reflex detection).
3.1.2 Through-Beam Sensors
Through-beam sensors have separate source and detector elements
aligned opposite each other, with the beam of light crossing the path
that an object must cross (Fig. 3.5). The effective beam area is that of
the column of light that travels straight between the lenses (Fig. 3.6).
FIGURE 3.5 Through-beam sensor.
Detector
Effective Beam
Field of View Field of View
Source
FIGURE 3.6 Effective beam area.
