Fiber Sensing

What are FOS and FOSS?

• FOS stands for Fiber Optic Sensing
• FOSS stands for ‘Fiber Optic Sensing Systems

How does fiber optic (or distributed) sensing work?

Sensuron’s distributed sensing technology uses 200-micron diameter glass fibers that have been continuously inscribed with Fiber Bragg Gratings (FBG). FBGs are the unique optical sensing element that turns ordinary telecom grade optical fiber into a powerful and robust sensing tool. These sensors act as embedded mirrors inside the fiber that reflect a specific wavelength. When an FBG fiber is bonded to a material and interrogated with light, the FBGs will reflect different wavelengths as the fiber is strained. This enables real-time monitoring of applications for precise measurement and unparalleled performance.

The following white papers provide a more in-depth description of Fiber Optics Sensing:

• Introduction to Fiber Optic Sensing
• Fiber Optics Sensing Fundamentals

What are the main differences between Strain Gauges and Fiber Optic Sensing?

Foil Strain Gauges (SG) are built based on the principle that the electrical resistance of the foil material changes due to mechanical elongation. The strain gauge technology is quite mature as they have been in use for decades. SGs come in different sizes, shapes, and accuracy. But SG technology has a few fundamental shortcomings in comparison to FOS technology.

The first important shortcoming is that every single SG needs its own 2/3-conductor wire from the gauge all the way to the signal conditioner or DAQ unit. The problems related to cable management makes establishing high-density distributed strain gauge systems impractical. This issue is totally absent in FOS which uses an optical fiber not only to measure strain but also to transfer measurement data to the DAQ unit. The weight savings achieved by the application of FOS is substantial when a high-density network of strain measurements is required for larger structures e.g., airplane wings, long-span beam-type structures, and pipes.

Second, SGs require tedious surface preparation and installation techniques which generally can only be performed by trained technicians to ensure consistency. Also high quality soldering is needed to ensure a reliable connection between wires and a gauge, otherwise the measurement may suffer from high noise and mediocre repeatability. The equivalent of soldering in FOS is splicing. However, splicing only needs to be performed once for each fiber supporting thousands of strain measurement points.

Third main shortcoming of SG technology is its intrinsic sensitivity to electromagnetic interference (EMI). According to a major SG manufacturer: “Virtually every electrical device that generates, consumes, or transmits power is a potential source for causing noise in SG circuits. The higher the voltage or current level, and the closer the SG circuit to the electrical device, the greater will be the induced noise.” A FOS system has no electrical conductor beyond the interrogator because optical fibers are made of glass and plastic protective jacket. Consequently, all measurements performed by optical fibers are completely immune to EMI.

What do Sensuron’s distributed strain and temperature sensing systems do?

Our technology makes the task of measuring multiple sensing points over large intricate surfaces easier by combining thousands of sensors on a single fiber. Beyond aerospace, medical, automotive, civil, and energy applications, Sensuron’s distributed strain and temperature sensing technology has the ability to:

Increase public safety: Sensuron’s technology monitors the structural health of aircrafts, buildings, nuclear equipment, dams, automobiles, trains, etc.

Save resources: Sensuron’s compact distributed sensing solutions lead to improved efficiency of wind turbines

Detect structural instabilities: Sensuron’s RTS125+ system monitors components and structures within tunnels, chemicals, or nuclear power plants

Enhance sensitivities: Sensuron’s technology improves the precision of medical instruments and industrial tools

Improve accuracy: Sensuron’s distributed sensing systems precisely measure liquid levels in vats of chemicals, cryogenic liquids, fuel, water, oil, etc.

The following white paper provides details on Distributed Strain and Temperature Measurements

How is it different from other fiber optic technologies?

There are many differences between our platforms and other FOS technologies; however, our technology is industry leading when considering the combination of spatial resolution, refresh rate, and sensing length. For more details, please visit our page on fiber sensing basics.

Sensuron’s distributed sensing technology combines the functions of a number of technologies, offering one solution that helps engineers solve problems across the aerospace, energy, automotive, civil, and medical industries. By improving the effectiveness of operations, our solution enables engineers to enhance their problem-solving capabilities.

By analyzing changes in real-time, Sensuron’s technology increases the reliability of measurement and improves the safety of applications in demanding environments. This enables engineers to focus their energy on innovating beyond the problems of today and focus on the future. To see how Sensuron can enhance your applications, visit our Applications page.

Technology

Is it fragile?

While Sensuron’s distributed sensing solutions are lightweight, embeddable and can be used in applications as delicate as minimally invasive surgery, they are among the most robust technologies on the market. Immune to EMI and chemically inert, Sensuron’s systems can operate effectively in hazardous and difficult physical environments. Impervious to temperatures ranging from -200 to 200°C, Sensuron’s technology will function effectively when legacy technologies would fail.

What can it withstand?

Unlike many legacy technologies, Sensuron’s solutions can withstand:

Temperatures between	-200 to 200°C
Operating fiber bend radius	.25 in
Fiber breaking point	.125 in

What is the size and weight of the interrogators?

• Summit: 330 x 305 x 115 mm (13 x 12 x 4.53 in), 6.6 Kg (14.6 lbs)
• RTS125+: 330 x 181 x 162 mm (13 x 7.13 x 6.38 in), 6.2 Kg (13.7 lbs)

What are the power requirements?

• Summit: 16 VDC, 65 W (laptop 110V AC adapter suffices, provided along with the instrument)
• RTS125+: 16 VDC, 80 W (laptop 110V AC adapter suffices, provided along with the instrument)

How do I interface with the device? Is software included?

All Sensuron devices contain an onboard Windows 10 PC. Users may interface with the device by connecting USB peripherals and using it as a standalone PC, or they may connect to and control it with an external Windows PC using an Ethernet connection. Software is included for control, data acquisition, data recording, and data visualization. Data visualization and real time post processing in third party software is possible using TCP/IP – Contact Sensuron for more details.

What is the acquisition rate?

The acquisition rate on the Summit ranges from 10 Hz to 60 Hz, and 10 Hz to 100 Hz on the RTS125+. The acquisition rate is an inverse function of the dynamic range. The larger the strain or change in temperature the user wants to sense, the slower the acquisition rate will be. The maximum rates for each device yield a range of approximately ±800 με, or a temperature range of -60 to +100 °C. The slowest acquisition rates for each device yield a range of approximately ±17,500 με, or a temperature range of -273 to 1600 °C. Standard sensor fiber will not operate above 200 °C. Please contact Sensuron for high temperature options.

Can you perform temperature compensation?

Yes, temperature compensated strain measurements are possible. This generally requires measuring the temperature or the thermal apparent strain directly. This is accomplished using either an unbonded portion of fiber, a second fiber, or a compensation tab. Please Contact Sensuron for more details.

Can you place the sensor far away from the interrogator?

The user has the option to add an arbitrary amount of standoff length between the data acquisition device and the sensor fiber up to a maximum length. The maximum lengths are 30 m and 50 m for the RTS125+ and Summit, respectively.Each channel may have a different standoff length. Lengths up to 2 km may be possible, Contact Sensuron for more details.

How do you install the fiber?

Fiber is installed using the same methods as traditional foil strain gauges. One must clean, abrade, and reclean the surface to which the fiber will be bonded along the entire intended path of the sensor. Then, the sensor is held in place along the path by “spot” gluing it in place. Finally, a thin layer of adhesive is applied continuously along the entire fiber length. The same adhesives used for installing foil strain gauges may be used for fiber sensors.

What installation materials are required?

Sensuron’s distributed sensing systems utilize similar installation tools used with strain gauges, including: abrasive (sandpaper), glue for tacking the fiber down along the route and optionally for the whole installation, epoxy as the alternative for the primary installation adhesive (cyanoacrylate glue for the tacking down), mixing tools, gloves, eye protection, fume protection, alcohol or other cleaning solvents, preferred installation tool for “smearing” the epoxy (a brush, a q-tip, your finger and a sheet of lint-free wipe), pencil, and measuring tools for marking the route.

What is the diameter of the fiber?

Sensuron’s sensing fiber comes in three configurations:

• 195 micron diameter
• 120 micron diameter
• 195 micron diameter fiber embedded within 500 micron or 1,000 micron diameter GFRP jacket (for concrete embedment)

What is the fiber coating?

Sensuron fiber is coated with a hybrid polymer material called ORMOCER. There are two types of ORMOCER coating available for use with Sensuron devices, which are optimized for certain application types. ORMOCER coated fiber is used for sensing strain, and ORMOCER-T fiber is used for sensing temperature.

What is it used for?

Sensuron’s compact FOS systems have a diverse array of applications. The technology can be used to test, monitor and control:

• Strain fields – By monitoring changes in strain fields in materials, Sensuron’s fiber sensing technology can help engineers evaluate durability and safety in structural health monitoring, validate finite element models, and verify structural designs.
• Temperature profiles – By streaming light through an optical fiber and observing the reflections, Sensuron’s technology can monitor minute changes in the temperature profile along the optical fiber. This provides an accurate picture of the integrity of materials in applications from oil wells to airplanes.
• 2d Deflection – Sensuron’s fiber sensing systems are able to determine the deflection of aircraft wings and other structures.
• 3d Shape – Sensuron’s shape sensing technology provides information readings along the entire length of the fiber. Immune to EMI and RFI, Sensuron’s solutions can be used in minimally invasive procedures to guide instruments like catheters and needles with precision in real-time.
• Distributed load – By monitoring the strain and stress characteristics of a distributed load throughout composite materials, Sensuron’s fiber sensing solutions can accurately reflect the integrity and health of a structure.
• Liquid level – Sensuron’s systems are capable of monitoring liquid level in cryogenic tanks which enables advancements in spaceflight and other applications.

For specific applications, of our technology, please visit the “Applications” page.

What other materials are required?

For installation, recommended materials include lint-free wipes, non-residue-leaving tapes (such as flash breaker tape), rulers, protractors, and any other helpful route-marking tools.

Can you have multiple connection points along a fiber line?

Yes, the Sensuron technology allows users to have multiple connection points along a single fiber line. This is accomplished by using multiple FC/APC patch cords (lead fibers) connected in series using FC/APC couplers, thus enabling modular installations and connections across bulkheads.

Does the system multiplex or do all channels operate simultaneously?

All eight channels are monitored simultaneously, in real time.

Can you protect it?

Yes, Sensuron’s fibers can be protected by a variety of sealants and tapes. To learn more, contact a Sensuron services engineer.

How does it adhere?

Sensuron’s distributed sensing systems adhere using the same materials as traditional foil strain gauge applications – typically a cyanoacrylate-based glue or a two-part epoxy for more critical and long-term installations. The substrate material is prepped by thoroughly cleaning the surface, abrading it, re-cleaning, tacking the fiber down to hold it along the desired route, and then applying the glue or epoxy. It is not unusual to install 2048 sensors in a single day.

How tightly can I bend the fiber?

Sensuron fiber may be bent to a radius of .25 inch during operation. Fibers will survive but not operate when subjected to bends as low as 1/8 inch.

Is it embeddable?

Sensuron technology can function independently or as an integrated component.

Is it easy to apply, maintain, use, and understand?

Sensuron provides all the necessary training on handling, installing, and maintaining our systems and fibers so that our customers will be successful. Most people find applying fiber comparable to the installation of strain gauges, however one fiber can act as thousands of strain gauges so the technology is much easier to install.

What ruggedized/environmental standards does the RTS125+ meet?

The unit has been ruggedized for general operation outside of a laboratory environment (full temperature range and vibration/shock profile subject to test). Sensuron invites customers to contact us so that we may investigate options for meeting specific environmental requirements.

How long will the technology last in demanding environments?

A well-done installation should last as long as it is needed. For example, NASA has aircraft with installations from eight years ago that have survived many hours of flight, technician abuse, as well as sitting out on the hot Edwards Air Force Base tarmac. In order to guarantee a well-done installation, Sensuron’s engineering services team is available to conduct onsite training and provide product integration services.

What happens if a sensor breaks?

If a sensor breaks, data may still be acquired up to the point of the break. Some users choose to connectorize the distal end of the broken segment, thus regaining the entire original sensing length at the expense of requiring an additional channel on the data acquisition device.

Working With Sensuron

How do I know what technical specifications I need?

At Sensuron, we recognize that your project may require custom packaging and tools to meet your size, weight and performance requirements. We will work with your team to ensure that your application can benefit from our distributed sensing solutions. Please contact us for more details.

What services do you offer?

The Sensuron engineering services team is comprised of experienced hardware, application, and design engineers whose mission is to ensure customers’ satisfaction and success. We provide technical services for customers or prospective customers interested in advanced onsite training, product integration, feasibility studies, technical research and many other requests. Training is provided so that customers can learn to operate distributed sensing equipment, apply fibers in their environment, determine how to achieve new testing standards, and evaluate data.

What tools are needed in addition to the distributed sensing system?

Sensuron will provide the fiber and any specialty sensors your application may require. See “what installation materials are required?” Q&A for information about tools needed to install our system with your application.