classic | mobile


SA Instrumentation & Control Buyers' Guide


Fibre optic sensing technology
March 2018, Sensors & Transducers

Fiber optics is used to transmit light energy over long distances. Optical fibres are thin, transparent strands of optical quality glass or plastic that can be as thin as a strand of hair. In photoelectric sensing, these fibres are used to transmit or receive light from the LED of a sensor.

The fibre consists of a glass or plastic core surrounded by a layer of cladding material and, for plastic fibres, jacketing. Glass fibres are arranged in bundles, and plastic fibres are usually packaged as monofilaments. Glass fibres do not have jacketing. Instead, the bundles are packaged in sheathing that is usually stainless steel flexible conduit, but may be PVC or some other type of flexible plastic tubing. A protective steel coil can also be used beneath the sheath to protect the fibre bundle.

Types of fibres

Glass fibre optics

Glass fibre optics is made up of a bundle of very small (usually about 50 micron diameter) glass fibre strands. A typical assembly consists

of several hundred fibres, protected by a sheathing material, usually a flexible armoured cable, which are mostly used in challenging environments, such as applications with high temperature, corrosive substances, or moisture.

Plastic fibre optics

Plastic fibre optics usually have a larger, monofilament core. It is not always bundled, and comes in a single strand of material typically 0,25 to 1,5 mm in diameter. Plastic fibres are typically used for more general purpose applications where they can tolerate extreme bending and be cut to length to fit in setups where space is limited.

How a fibre optic system works

How optical fibres transport light rays can be explained using the principle of total internal reflection. This states that any ray of light hitting the boundary between the core and the cladding (which have different densities) will be totally reflected, provided that the angle of incidence is less than a certain critical value. The light beam is transported all the way through the tiny fibre by reflection, exiting at the same approximate angle as it entered the fibre.

There is, however, a tendency for the signal to degrade over distance. Attenuation of the signal will occur, depending on the purity of the core material.

Fibre optic assemblies

A fibre optic assembly determines the sensing mode. Therefore, the type of fibre that is chosen determines the assembly required by the application.

Individual fibre optic assemblies

Individual fibre optic assemblies simply guide light from an emitter to a sensing location or from the sensing location back to a receiver. The configuration determines the sensing mode and individual assemblies are usually used in pairs for opposed-mode applications.

Bifurcated fibre optic assemblies

Bifurcated optics conducts the emitted light together with the received light via two branches, consisting of different fibres, within one fibre optic assembly. This allows a single sensor to both illuminate and view an object through the same optic assembly.

If an object appears in front of the sensing end of a bifurcated assembly, light from one branch will be reflected off the object and back to the receiver through the other branch. Bifurcated assemblies are typically used in diffuse mode sensing and can also be used in retro-reflective sensing applications.

Typical applications for fibre optics

Because of the inherent attributes, fibre optics are ideal in the following applications:

• Vibratory feeders

• Conveyors

• Pill counting

• Small object detection

• Ovens

• Robotic arms and moving machines

For more information contact Brandon Topham, RET Automation, +27 (0)11 453 2468,,

Supplied By: RET Automation Controls
Tel: +27 11 453 2468
Fax: +27 11 453 2406
Share via email     Share via LinkedIn   Print this page

Further reading:

  • Fibre optic sensors for detecting hot rollers on conveyors
    March 2018, Spero Sensors & Instrumentation, Sensors & Transducers
    The use of modern fibre optic sensors based on DTS (distributed temperature sensing) technology has established itself as a proven method for fire detection and temperature measurement.
  • SICK launches a new generation of photoelectric sensors
    March 2018, SICK Automation Southern Africa, Sensors & Transducers
    By focusing on the essentials, SICK has made its photoelectric sensors fit to face future challenges.
  • Telco sensors for elevator ­management
    March 2018, Gail Norton Instrumentation, Sensors & Transducers
    The Space Motion Series SMM 01 from Telco Sensors operate on the Doppler radar principle to detect motion in a defined area by means of microwaves using the latest sensor technologies. With its compact ...
  • Turck adds IO-Link to ultrasonic sensors
    March 2018, RET Automation Controls, Sensors & Transducers
    Turck has added a variant with an IO-Link output to its basic Compact series of ultrasonic sensors. Users can use IO-Link for the process values or continue to use the switching output of the sensor. ...
  • Ready for any application – the W16 and W26 photoelectric sensors
    March 2018, SICK Automation Southern Africa, Sensors & Transducers
    SICK Automation’s W16 and W26 photoelectric sensor product families represent a new generation of photoelectric sensors. The company has streamlined its portfolio of object detection sensors and improved ...
  • Stainless steel sensors offer ­optimum protection
    March 2018, ifm Electronic RSA, Sensors & Transducers
    The new full-metal sensor ranges from ifm are used wherever an application presents particular challenges to the mechanical design. In the food industry, for example, not only rapid changes of temperature ...
  • Telco sensors for refrigeration and storage
    February 2018, Gail Norton Instrumentation, Sensors & Transducers
    Mobile racking enables compact storage while keeping the stored pallets individually accessible. Where storage space is expensive, for example in cold stores, mobile racking is the perfect solution. Telco ...
  • Product quality, verification and package inspection
    February 2018, Westplex, Sensors & Transducers
    In addition to improving material handling, logistics efficiency, product quality and package safety and integrity, machine vision can also be implemented on the processing side to reduce scrap, improve ...
  • Sensor solutions for packaging applications
    February 2018, Countapulse Controls, Sensors & Transducers
    Modern packaging plays an important role in preserving, protecting and selling a host of products, from items small enough to need tweezers to be picked up to those that need a forklift to be moved. Packaging ...
  • Hygienic biofilm monitoring sensor
    February 2018, Instek Control, Sensors & Transducers
    Bacteria settles among any structure (pipelines, tanks, machinery) in contact with water in a very short time, if appropriate preventative measurements are not applied. The term biofilm refers to the ...
  • Early fire warning prevents losses at waste to energy facility
    February 2018, FLIR Systems, Sensors & Transducers
    For companies involved in waste management, spontaneous fires are a fact of life and the critical issue is, therefore, to detect an outbreak as efficiently as possible and prevent it from spreading. For ...
  • New vibration switch protects critical assets
    February 2018, R&C Instrumentation, Sensors & Transducers
    As part of the recently introduced RC range of vibration sensors, R&C Instrumentation has launched a new compact vibration switch, designed to protect machinery against unexpected shutdown and repair costs. ...

Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Terms & conditions of use, including privacy policy
PAIA Manual


    classic | mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.