Page 181 - Sensors and Control Systems in Manufacturing

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T h ree
Cha p te r

Cladding
Plastic or glass fiber
LED Emitted
Light
Light energy
Plastic or glass
fiber end view
FIGURE 3.14 Total internal refl ection.

electronics, they can operate in much higher temperatures—as high
as 400°F—and in areas of high vibration. They are limited by sensing
distances, which typically are 80 mm in the proximity mode and 400
mm in the through-beam mode. Also, because of their small sensing
area, optical fibers can be fooled by a small drop of water or dirt over
the sensing area.
Fiber optics is used to transmit data in the communication field
and to transmit images or light in medicine and industry. Photoelec-
tric controls use fiber optics to bend the light from the LED source
and return it to the detector so sensors can be placed in locations
where common photoelectric sensors cannot be applied.
Fiber optics used with photoelectric controls consists of a large
number of individual glass or plastic fibers that are sheathed in
suitable material for protection. The optical fibers used with photo-
electric controls are usually covered by either PVC or stainless-steel
jackets. Both protect the fibers from excessive flexing and the envi-
ronment (Fig. 3.15).
Optical fibers are transparent fibers of glass or plastic used for
conducting and guiding light energy. They are used in photoelectric
sensors as “light pipes” to conduct sensing light into and out of a
sensing area.
Glass optical-fiber assemblies consist of a bundle of 0.05-mm-
diameter discrete glass optical fibers housed within a flexible sheath.
Glass optical fibers are also able to withstand hostile sensing environ-
ments. Plastic optical-fiber assemblies consist of one or two acrylic
monofilaments in a flexible sheath.

FIGURE 3.15 Jacketed glass fi bers.