Fiber Optic Sensing vs Legacy Technology
Strain gauges and thermocouples have long been the standard for measuring strain and temperature during testing. While these technologies have been good enough for decades, they are not always able to effectively test and monitor the innovations of today. The limitations of legacy technology are not about accuracy, rather it is primarily about the level of insight provided by the data. Strain gauges and thermocouples only provide points of information, while some types of fiber optic sensors can provide spatially continuous data along the entire length of the fiber. As a result, engineers can measure strain fields and temperature distributions on a structure in order to better understand how the component behaves under different conditions. While point sensors only allow engineers to monitor critical points, distributed (spatially continuous data) sensors can measure what happens at critical points and everywhere in between. This level of insight is invaluable when it comes to designing with new composite materials. Additionally, fiber optic sensors can be embedded in materials in order to provide greater insight into the internal behavior of composite components and structures.
Fiber Optic Sensing Basics
Sensuron offers intrinsic fiber optic sensing technology, whereby the fiber optic cable itself is the sensor. Within the division of intrinsic sensors, there are, generally speaking, three generations of technologies: point fiber bragg grating (FBG) based sensors, scattering and spatially continuous FBG based. Scattering techniques take fully distributed measurements while FBG techniques can have a handful of sensing points or be fully distributed depending on how the system interprets the signal from the sensing element.
FBGs act as miniscule mirrors and are manufactured into the core of the fiber. As light travels down the fiber, each grating reflects a portion of the signal back to the system. The system recognizes changes in the returning signal and interprets this information to provide accurate strain and temperature measurements. Most FBG based systems have a handful of sensing points along each fiber. While this multiplexing capability was a step forward from legacy technology, it still cannot provide the sensor density required for monitoring between critical areas. Some strengths of point FBG sensors include precision, the ability to perform dynamic tests, and high speed data acquisition.
Scattering techniques do not use FBGs at all, but depend on imperfections in the fiber optic cable to attain readings. There are three different types of scattering technologies used in sensing systems today and each has different capabilities. Generally speaking, scattering based fiber optic sensing systems benefit from distributed data and long sensing lengths. They are, however, subject to low data fidelity, very slow data acquisition rates on the order of minutes, and are susceptible to vibration limiting them to static operation.
Sensuron applies a technique that incorporates the strengths of point FBG sensors and scattering based systems. Sensuron uses FBGs as the sensing element in our fiber, but inscribes them continuously along the entire length of the fiber. This, along with the technique used to interpret the signal, enables our platforms to take spatially continuous data while retaining the precision, dynamic testing, and high acquisition rates afforded by using FBGs. This allows engineers to obtain precise measurements of full strain fields, temperature gradients and other parameters in either static or dynamic environments. Using the distributed strain data provided by the fiber, Sensuron’s platforms can also measure internal and applied loads, deflection, 3D shape and liquid level.
At Sensuron, we see a sensing market at the cusp of a transition from point sensors to distributed sensors and smart data acquisition devices that can measure more than one parameter at a time. Existing data acquisition hardware is capable of supporting multiple sensor types, however, the weight of the cables and tedious installation of sensors make legacy solutions cumbersome to deploy. Multi-sensing platforms, simply put, are sensor technologies that can monitor multiple parameters (strain, temperature, deflection, etc.) simultaneously and are robust enough that they can be deployed in multiple applications across an organization and utilized throughout the product lifecycle. It’s not just about being able to monitor different parameters using the same data acquisition hardware. More than that, a multi-sensing platform can consolidate sensing technology so the same hardware, with minor changes in application techniques, can adapt to cover multiple testing and monitoring needs of an organization. In order to accomplish this, the sensing system must obtain spatially continuous information in real time, be capable of taking dynamic measurements, be able to easily integrate with a network and perform well in the lab or harsh environments. These features allow multi-sensing platforms to be deployed in lifecycle monitoring applications from design validation to providing operational data for critical components and equipment.
Download our Introduction to Fiber Optic Sensing white paper for more information about the technologies discussed here.