Detection based on “light”
What is a fibre optic sensor?

Outline

The fibre optic sensor has an optical fibre connected to a light source to allow for detection in tight spaces or where a small profile is beneficial.

Principle and major types

Optical fibre configuration

The optical fibre consists of the core and the cladding, which have different refractive indexes. The light beam travels through the core by repeatedly bouncing off the wall of the cladding. The light beam, having passed through the fibre without any loss in light quantity, is dispersed at an angle of approximately 60° and emitted to the target.

The cores are divided into the following types:

Plastic type

The core of the plastic-fibre consists of one or more acrylic-resin fibres 0.25 to 1 mm in diameter, encased in a polyethylene sheath. Plastic fibres are light, cost-effective, and flexible which is why they are the most common type of fibre sensor.

Glass type

The glass-fibre consists of 10 to 100 µm diameter glass fibres encased in stainless steel tubing. This allows it to be used at high operating temperatures (350°C max.).

The optical fibre sensors are divided into two categories: thrubeam and reflective. The thrubeam type comprises a transmitter and a receiver. The reflective type, which is a single unit, is available in 3 types: parallel, coaxial, and separate. The 3 are based on the shape of the crosssection of the optical fibre.

Type Description
Parallel
Parallel
Generally used for plastic fibres.
Coaxial
Coaxial
High-precision type, consisting of a core (transmitter) and surrounding area (receiver). The operating position can remain the same regardless of the direction from which the target enters the detecting area.
Separate
Separate
This type, containing several 10µm glass fibres in diameter, has separate areas for the transmitter and receiver.
Type Description
Parallel
Parallel
Generally used for plastic fibres.
Coaxial
Coaxial
High-precision type, consisting of a core (transmitter) and surrounding area (receiver). The operating position can remain the same regardless of the direction from which the target enters the detecting area.
Separate
Separate
This type, containing several 10µm glass fibres in diameter, has separate areas for the transmitter and receiver.

INDEX

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