Fibre optic strain gauges, known as Fibre-Bragg-Grating Sensors, measure changes in strain caused either by external stresses or temperature-related issues depending on the configuration selected.
The FBG Sensors are special structures constructed in a short segment of optical fibre which, depending on their linear expansion, block and therefore filter certain wavelengths of light. A special coating gives the optical fibre robust characteristics so it is particularly suited for use in extreme environments.
The base unit of measurement of an FBG is 1cm. In one optical fibre there can be several FGBs in series or radial arrangement. The sensors are pre-assembled in special mouldings and/or sensor housings and so can be glued or welded onto the object to be measured or be embedded into a structure (e.g. concrete, geogrid, back-fill material).
The non-sensitive area of the supply line can vary in length between 100 metres up to a few kilometres. Only one signal fibre per measuring channel is needed.
The measurement system consists of the FBG sensors, the data analyser, components for power supply (plug, fibre splicing socket, power supply cable) as well as a computer for controlling and interpreting of data.
FBG – Sensors
- are well suited for use in extreme environments
- are unaffected by electromagnetic fields and high voltage
- are explosion-proof
- have a considerably longer life span than standard strain gauges
- because of their small size can be employed in confined spaces and in structures which are not accessible at a later time
- have the capability to detect strains as small as the µm range (micrometeres) and can therefore be used as an early warning system
- need only one supply fibre per measuring channel
Parameters of the Measurement Technology:
|Measurement cycle:||1/100/1000 readings per second (device specific)|
|Max. No. of FBGs per channel:||generally 10-13 (load dependent)|
|Deformation range:||+/– 0.5% accuracy over 10 million load cycles|
|Range per channel:||100 m up to 2 km|
|Number of channels:||1 or 4|
|Multiplexer:||from 1 to 4 (a total of max. 16 channels)|
|Interface:||Ethernet (for set-up and data transfer)|
Configurable software modules allow customer specific methods for collection, recording, visualisation, remote transmission and processing of data.
The measurement technology can be used as a temporary installation or as a permanent online monitoring service, which can also be integrated into operational control systems and data logging systems.