Smart Sensors Flashcards
What are the advantages of fibre technology in smart sensing?
Can perform integrated, quasi-distributed and distributed measurements
What are different types of smart sensors (FOS)?
Point sensor (Fabry-Perot)
Quasi distributed/multiplexed (Fibre Bragg Grating)
Long-base (SOFO)
Distributed (Brillouin and Raman)
How do fibre optic sensors work?
Optical fibre (a transparent guiding medium/material, made of glass or plastic) guides the information-carrying light waves
Transmits light between the two ends of the fibre
What properties can fibre optic sensors monitor?
- Strains
- Vibrations
- Accelerations
- Linear and rotary positions
- Temperatures
- Pressures
- Chemical concentration
- Electrical fields/currents
What are the advantages of fibre optic sensors?
Better long-term stability and reduced noise
Non-conductivity
- immune to electromagnetic and radio frequency interference
Flexibility
- multiplexing and distributed sensing
- long-distance remote monitoring
Convenience
- light
- small diameter
- embeddable
Reliability
What are the disadvantages of fibre optic sensors?
Highly skilled staff required for maintenance
High-cost:
- the precise instruments are expensive
Only point-to-point working is possible
Joining of fibres is time-consuming
What is the difference between single-mode and multimode fibres?
In single-mode fibre, only the fundamental mode is propagated:
- travels through fibre without reflection at the core-cladding boundary
- higher bandwidth
- smaller core diameter
In multimode fibre, higher-order modes are propagated (in addition to the fundamental):
- different modes travel in curved, wavelike paths
- lower bandwidth
- higher core diameter
What do Fabre Perot sensors measure?
Give an example use
They are point sensors for strain, deformation, temperature, pressure
- commonly used for geotechnical projects (dams and slopes)
Used on the El-Mauro Tailings Dam
- measuring pressure and temperature
What are the advantages of Fabre Perot sensors?
High resolution and accuracy
Small size
Lowest cost (for geotechnical)
Temperature insensitive
What are the drawbacks of Fabre Perot sensors?
They are multiplexing
- complexity, signal interference*
Give an overview of quasi-distributed/Fibre Bragg Grating systems
Give an example case study
They are multiplexed strain and temperature monitoring systems:
- static and dynamic measurements
- replacing traditional strain gauges
Example - monitoring rockslide in the Alps (Switzerland)
- dynamic measurements for correlation of movements with micro-seismic activity
What are the advantages of Fibre Bragg Gratings?
In-line multiplexing
Well-suited for challenging environments (e.g. in oil and gas)
Small size
- can be embedded in composites
What are the drawbacks of Fibre Bragg Gratings?
Temperature compensation
Accurate and stable demodulation
Give an overview of SOFO systems
Give an example case study
SOFO systems are long-gauge fibre optics for measuring deformation
Case study - Luzzone Tunnel Excavation:
- measuring deformation at different excavation phases
- purpose was to optimise the shotcrete thickness
What are the advantages of SOFO systems?
Long gauge
High resolution
Accurate, insensitive to:
- temperature
- EM field
- corrosion
Embeddable or surface installable in new and existing systems
- easy installation
Automatic and remote operation
Give an overview of distributed sensing
Give an example use
Used for temperature and strain monitoring of numerous points:
- used for localisation (ie. reading unit locates where the problem(s) are)
Example use - tunnel monitoring:
- deformation monitoring
- crack detection and localisation
Give a case study example for distributed sensing
Penstock monitoring in Switzerland
