Page 176 - Sensors and Control Systems in Manufacturing

Fiber Optics in Sensors and Contr ol Systems
Because the light from the source is transmitted directly to the 137
photodetector, through-beam sensors offer the following benefits:

• Longest range for sensing
• Highest possible signal strength
• Greatest light/dark contrast ratio
• Best trip point repeatability

The limitations of through-beam sensors are as follows:
• They require wiring of the two components across the detec-
tion zone.
• It may be difficult to align the source and the detector.
• If the object to be detected is smaller than the effective beam
diameter, an aperture over the lens may be required (Fig. 3.7).

3.1.3 Reflex Photoelectric Controls
Reflex photoelectric controls (Fig. 3.8) position the source and detec-
tor parallel to each other on the same side of the target. The light is

FIGURE 3.7 Sensor with aperture over lens for detecting small objects.

FIGURE 3.8 Refl ex photoelectric controls.