What's up

An optical fiber is built to carry light from one point to another. Change the glass in the right way and it starts doing something else. It measures what happens to it along the way.

A demonstrator built on that principle has just been installed in our building, and here is what it does.

Where electrical sensors stop

Most industrial measurement still runs on thermocouples, strain gauges and other electrical sensors. They are cheap, well understood and perfectly adequate until the environment turns against them, which in industry it regularly does. Heat degrades them. Electromagnetic fields around high-power equipment disturb their signal or force expensive shielding. Corrosive atmospheres eat them, and every additional measurement point means another cable run back to the cabinet.

Those limits come from the way the sensors work, so no amount of engineering removes them. A fiber optic sensor gets around them by measuring in a completely different way.

Measurement happens inside the glass

An optical fiber is a strand of glass about as thin as a human hair. To turn a short length of it into a sensor, a laser modifies the glass from the inside, changing how strongly it bends the light passing through, and repeating that same change at very regular intervals. Nothing is added to the fiber and nothing is cut into it. The glass simply comes out slightly different, and stays that way for good.

That repeating modification is called a Fiber Bragg Grating, or FBG. It works as a very selective mirror. One precise wavelength bounces straight back, everything else carries on down the fiber.

Heat the fiber or deform it and the spacing between those modified zones changes ever so slightly. The wavelength coming back shifts with it. Measure that shift and you know what happened at that exact point.

The relationship is linear, which is what makes it usable in the field. A given shift means a given temperature or a given strain, every time. Since each grating reflects its own wavelength, several dozen measurement points can share a single fiber, each reporting independently, with several fibers running in parallel into the same instrument.

The fiber carries light and not current, so electromagnetic interference has nothing to act on. Glass does not corrode. With the right packaging, the sensor survives the temperatures found inside an industrial furnace. That is how the technology ends up in metallurgy, glassmaking and cement, in aerospace and defense composites, in energy, construction and geothermal installations.

Three measurements on one board

Our demonstrator puts three systems side by side, each standing in for a real application.

• A small electric train runs over an instrumented track. Every axle that passes presses down on the fiber underneath and the system counts it. That is axle counting, how rail operators know a train is on a section and how long it is
  
  
• A heating lamp sits inside a cylinder, deliberately off center, standing in for an industrial furnace. The fiber reads temperature along its whole length and draws the gradient that off-center source creates. A single point probe would report one number and miss the hot spot entirely.
  
  
• A composite plate is pressed, and the fiber bonded to it turns that deformation into a force reading. This is the basis of structural health monitoring, where the sensor is embedded in the composite during manufacturing and keeps reporting for the rest of the part's life, including on internal damage that no external inspection would reveal.

Where the gains show up

On a furnace, a continuous thermal map means drifts and hot spots are seen as they appear rather than after the damage is done. Firing becomes more even, unplanned stoppages become rarer, and maintenance moves off a fixed calendar and onto the actual state of the equipment.

On a composite part, sensors embedded during manufacturing report on the curing cycle itself, which cuts rework and scrap before the part ever leaves the shop. Once it is in service the same fiber keeps reporting, so inspection can be planned on evidence rather than on a schedule, and the part spends less time immobilized for checks that find nothing.

One gain applies everywhere. Dozens of measurement points travel on a single fiber and a single cable run, where a conventional installation needs one run per sensor. B-SENS has put numbers on all of this for furnaces and for critical composite structures, and we are happy to pass them on to anyone who asks.

Sensor with nothing to attack

There is a second reason this demonstrator sits in our building.

An FBG sensor holds no firmware, runs no software and exposes no network port. Nobody can update it remotely, and nobody can compromise it remotely either. At a moment when connected industrial equipment has become a security question, and European law is about to require a cybersecurity case for machines, a fully passive measurement chain deserves a look.

The whole measurement chain comes from Mons

The system was designed and installed by B-SENS, a Walloon company based in Mons and born out of University of Mons research on fiber optic sensing.

The sensors, the interrogator that reads them and the software that displays the measurements all come from that same company. For anyone who cares where their measurement chain is designed and supported, that counts for as much as the specification.

That is what a demonstrator is for, connecting companies like this with those facing real measurement challenges.

Come and see it work

The demonstrator is now up and running. Come see how a fiber can measure a train, a furnace and a composite plate, then bring us your toughest measurement challenge and let’s see if we can crack it together.