This article aims to help system integrators and engineers choose the right components for multi-physics optical monitoring solutions. This is crucial, as all major structures – such as bridges, buildings, pipelines, and tunnels – are exposed to factors that cause strain and degradation. Without reliable and accurate monitoring of strain, temperature and other physical parameters, malfunctions and structural issues might not be detected, resulting in disasters.
In the following, we’ll discuss structural health monitoring (SHM) as a discipline, and we’ll show you how a typical optical Fiber Bragg Grating (FBG) based measurement chain – hosting several sensors in one optical fiber, interrogators, and PC software – can easily be designed.
Since the 1940s, the resistive strain gauge has been the benchmark for structural strain monitoring [9]. But certain limits come along with resistive strain gauges and sometimes hinder easy and reliable measurement.
For example, the number of electrical cables needed can be a challenge. This is because long cables are costly, and lots of them can become difficult to manage when used in large scale structures with many measurement spots [10], despite the existence of technical solutions for measuring electrical strain over distances up to several hundred metres, and to both technologies [4].
Optical sensors that are based on Fiber Bragg Grating (FBG) technology offer an attractive alternative to conventional electrical measurement chains.
This is because FBG technology has advantages such as multi sensors in a single optical fiber, overall lightweight passive design, and low attenuation, which allows long distance installation. This technology is also immune to electromagnetic interference (EMI), and sensors are more environmentally stable than electrical strain gauges (so they can withstand harsh conditions). They’re also competitively priced when it comes to a medium to high channel count and total cost of ownership [12, 13].
Thanks to the fact that it can be easily used with your supplier’s software, and is also integrated into any individual PC, FBG technology has acquired a large market share over time. It’s now used in a wide range of sensing applications [13].
For instance, it’s used in different health monitoring applications in civil engineering, including road and railway infrastructure, but also in geo-structures, oil and gas, hull monitoring of vessels in the marine industry, aerospace structures, and automotive temperature validation.
For a complete optical measurement chain, having the right sensor is only one third of the solution. You also need the right optical interrogator, and the right software in place to get overall reliable results.
And these three parts – sensor, interrogator, and software – complete your optical measurement chain.
In short, the sensor is what measures or ‘senses’ strain, temperature, acceleration, force or even tilt. The optical interrogator (the second component in the chain) is also known as a data acquisition system. It’s an optoelectronic instrument which ‘reads’ the FBG sensors. And the software is what allows you to view, record and analyse your measurement data.
Optical sensors based on Fiber Bragg Grating technology have many advantages over conventional resistive strain gauges. Both sensor types can also complement each other in various applications, from civil infrastructure and aerospace, to lab testing and energy.
But to make use of these advantages, you need to choose the right sensors, interrogators and software for your optical measurement chain. Our hope is that this brief primer can help engineers and system integrators make the right decisions when it comes to accurate and reliable strain measurements.
Be the first to learn more about the new MXFS optical interrogator for structural health monitoring.
Engineers worldwide rely on accurate and reliable measurement data acquired using sensors, interrogators, and software from HBM.
For instance, our optical sensors from the newLight product line – based on FBG technology – allow large strain measurement ranges with long-term stability. These sensors are the best choice for SHM (Structural Health Monitoring) due to their fast and easy installation and suitability for harsh environments.
On the optical interrogator side, HBM instruments provide high-resolution static and dynamic measurements 24/7. For instance, we have developed the brand new MXFS model for structural health monitoring. Along with our optical sensors, this interrogator helps you ensure a seamless measurement chain.
Lastly, HBM’s software is the final link in your optical measurement chain. Our data acquisition software (such as catman) manages millions of datasets and helps you get your results quickly.
One key advantage of HBM products is the possibility to mix and match sensors, interrogators, and software to suit your needs. We offer a complete product portfolio for SHM, giving you everything you need for accurate and reliable strain measurements. Table 1 below shows the compatibility of HBM interrogators and software. For more information on these products and on how to choose the right components for your optical measurement chain, please contact us.
BraggMONITOR | catman | |
FS22SI | YES | YES |
FS22DI | YES | YES |
FS42PI | YES | NO |
MXFS | NO | YES |
[1] Engineering.com, “Italy’s Morandi Bridge Collapse—What Do We Know?”, 2018.
https://new.engineering.com/story/italys-morandi-bridge-collapsewhat-do-we-know
[2] Alampalli, S., Ettouney, M., “Role of Structural Health Monitoring In Bridge Security”. Bridge Structures 4(3,4), 143-154, 2008.
https://www.researchgate.net/publication/245494458_Role_of_structural_health_monitoring_in_bridge_security
[3] E.Cheilakou et al. “Strain Monitoring System For Steel And Concrete Structures” Procedia Structural Integrity 10, 25-32, 2018.
https://www.sciencedirect.com/science/article/pii/S2452321618300532
[4] Cristina Barbosa “Optical Fiber Sensors vs. Conventional Electrical Strain Gauges for Infrastructure Monitoring Applications”, HBM.
[5] U.S. Department of Transportation, Federal Highway Administration, “State of the Practice and Art for Structural Health Monitoring of Bridge Substructures” (No. FHWA-HRT-09-040)], 2014.
https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/09040/
[6] American Society of Civil Engineers, 2017 Infrastructure Report Card, 2017.
https://www.infrastructurereportcard.org/cat-item/bridges/
[7] National Research Council Canada (NRCC), Construction Innovation, “Critical Concrete Infrastructure: Extending The Life of Canada’s Bridge Network”.
https://www.nrc-cnrc.gc.ca/ci-ic/en/article/v18n1-5/
[8] Gastineau, A., Johnson, T., & Schult A. “Bridge Health Monitoring and Inspections–A Survey of Methods”, Minnesota Department of Transportation, 2009.
https://www.researchgate.net/publication/282912591_Bridge_Health_Monitoring_and_Inspection_-_A_Survey_of_Methods
[9] The Strain Gauge User’s Handbook, Chapman and Hall, 1992.
https://books.google.co.uk/books?id=YrNr00vhF_gC&printsec=frontcover&dq=resistive+strain+gauges&hl=en&sa=X&ved=0ahUKEwjBxdDgxMvjAhVJTsAKHWQlAroQ6AEIKjAA#v=onepage&q=resistive%20strain%20gauges&f=false
[10] Ramakrishnan et al. “Overview of Fiber Optic Sensor Technologies for Strain/Temperature Sensing Applications in Composite Materials”, Sensors, 16 (1), 99, 2016.
https://doi.org/10.3390/s16010099
[11] Vishay Precision Group, “Noise Control in Strain Gage Measurements” Tech Note TN-501-2.
[12] Sabri et al.“Fiber Optic Sensors: Short Review and Applications”, DOI: 10.1007/978-981-287-128-2_19, 2015.
https://www.researchgate.net/publication/278680033_Fiber_Optic_Sensors_Short_Review_and_Applications
[13] Campanella et al., “Fibre Bragg Grating Based Strain Sensors: Review of Technology and Applications”, Sensors, 18(9):3115, 2018.
https://www.researchgate.net/publication/327710750_Fibre_Bragg_Grating_Based_Strain_Sensors_Review_of_Technology_and_Applications
[14] Peters et al. “Fiber Optic Sensors For Assessing And Monitoring Civil Infrastructures”, Sensor Technologies for Civil Infrastructures, 1, 121-158, 2014.
https://doi.org/10.1533/9780857099136.121
[15] Ma et al. “Fiber Bragg Gratings Sensors for Aircraft Wing Shape Measurement: Recent Applications and Technical Analysis”, Sensors (Basel), 19(1): 55, 2019.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6339136/