Brochure

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Fiber optics Technical information
Fiber optics
Item
Principle of operation Fiber optic photoelectric sensors comprise two parts, the amplifier and the
sensing head. The amplifier contains the emitter (the light source) and receiver
(detector) along with their associated electronics. The fiber optic cable is the
means used to transfer the light to the sensing head.
The light source (an LED) transmits the light beam down the fiber optic cable
by repeatedly reflecting the light off the boundary between the fiber core and
its sheath. When it reaches the end of the fiber the light is dispersed at the end.
When the light is dispersed it spreads out and forms a beam much like that
of other sensors, but on a smaller scale. With smaller light sources and lens
areas the sensing ranges are on the whole much shorter.
Types of fiber Fiber optic heads mainly split into two types, through-beam and diffuse
(although there are a few retro-reflective types). The principle of operation
of both types is exactly that of standard photoelectric sensors.
Construction Standard fiber: Most fiber optic sensing heads use this configuration of fiber
(i.e. a single fiber covered by a protective sheath). The fibers are usually plastic,
0.5 to 1 mm in diameter and covered in a plastic protective sheath.
Coaxial fiber: This gives greater accuracy. The core is used as the transmitter
and the surrounding fibers are bundled together to form the receiver. This gives
better accuracy, the target can enter the detecting area from any direction.
Multicore: These consist of large numbers of small fibers. This results in a more
flexible cable (E32-R types) which can literally be tied in a knot.
Robotic: In robotic fibers the multicore fibers are manufactured without fixa-
tion. This allows them to move freely reducing mechanical stress when the fiber
is bent.
LED
approx. 60°
Light
Sheath
Core
Matchstick
Fiber
Sheath
Receivers
Transmitter
Fibers
Sheath