Fiber Optic Sensors: Temperature, Pressure, And Strain

By Author: ADVAN
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Fiber optic sensors

As the building of infrastructure has become more and more precise over the years, so have the tools for measuring its performance. Sensors are installed on large works to ensure that the structure conforms to the standards set out prior to construction. There are other uses for sensors, too, such as physical security and lighting systems.

In recent years, fiber optic sensor systems have become a leading form of sensors for these applications. They are small, lightweight, and very easy to install. They are also weatherproof, as they contain no moving parts, and they are impervious to electromagnetic interference. This makes them suitable for high temperature applications, as well as high voltage spaces and areas exposed to the elements.

Fiber optic sensors work by transmitting light via laser down a fiber optical cable. They detect mechanical strain, temperature, chemical changes, rotation, pressure, and vibrations. They do this by measuring the difference in light patterns that are recorded by systems called FBG Interrogators.

Fiber ...
... optic sensors are passive, require no electrical power, and emit no signal. Fiber optic sensors offer increased reliability over traditional electro-mechanical sensors due to their resistance to electromagnetic and radio frequency interference, lightning, and corrosion.

This post covers three fundamental types of sensors, how they work, and an example of their applications.

Fiber optic temperature sensors

Fiber optic temperature sensors are based on the absorption of photons into gallium arsenide crystals. Sensors made from these crystals shift the transmission spectrum to higher wavelengths. As the sensor detects higher temperatures, the real-time measurement occurs, and the data is transferred to an FBG Interrogator that collates the information and turns it into useful data.

Applications: Manufacturing, oil and gas, mining, hospitality, aviation

Fiber optic sensor for pressure measurement

In the most basic sense, fiber optic pressure sensors restrict the amount of light transferred down an optical fiber cable when pressure is applied to it. As more pressure is applied, more light is blocked, and the detector recognizes this drop in light as pressure. The increase or decrease in light is measured and turned into meaningful data in real time. Because they are immune to electromagnetic interference, optical sensors make an excellent choice in high voltage applications and can be useful in the medical field because they contain no toxic materials.

Applications: Physical security barriers, parking systems, manufacturing

Fiber optic strain sensor

Fiber optic cables contain hair-like strands of fiber that transmit photons. At the core of these sensors is a series of etchings called Fiber Bragg Gratings that reflect and absorb light in a certain pattern. As the material is stretched, the Fiber Bragg Gratings are deformed, and the difference in the reflections and absorption of the light inside the optical fiber is measured and translated into data on how far the material has stretched. Their slim profile allows them to be embedded in the structure itself, providing richer, more reliable data on strain.

Applications: Bridges, transport, reliability, manufacturing, aviation, wind turbines