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Thijs Haselhoff, New Business Development Manager at Altheris Sensors & Controls and Eric Préfontaine, Business Development Manager at OpSens Solutions, responsable for the Energy market, together tell PES about this new state-of-the-art technology and explain why fibre optic sensors are perfectly suited to the Renewable Energy market.

PES: Welcome to PES magazine. Thanks for talking with us. Would you like to begin by explaining a little about the background of your organisation and how you currently serve the offshore industry?

Thijs Haselhoff: Altheris is a specialised partner for sensors, instrumentation, measurement systems and industrial joysticks for OEM, Test & Measurement and Automation Control Applications. We turn every measurement challenge into a sensor solution and advise and help you every step of the way. Altheris and the Althen group have established a partnership with OpSens Solutions based in Canada for fibre optic sensors. Altheris is a member of the Althen Sensors & Controls group with its offices in the Netherlands, Germany, France and the USA.

PES: Fibre Optic Sensors that doesn’t sound new to me?

Eric Préfontaine: Measurement solutions based on fibre optics have indeed been present for quite some time. That’s why fibre optic sensors don’t sound innovative. But a few years ago a new fibre optic technology came on the market based on White Light Polarisation Interferometry (WLPI), which offers great benefits over its older competitors, who are using fibre optic technologies such as Fibre Bragg Grating (FBG).

PES: What is the difference between your technology and other optical technology? 

EP: In other technology such as FBG, the fibre optic is part of the sensing system. If stress is applied on the fibre optic, it changes the value you are trying to read and that is a major problem. FBG is also affected by temperature. The Altheris fibre optic sensors are not affected by sagging or bending the fibre optic, for example in the sagging of the blade. This is because the fibre is just a means to carry the signal. The sensor is located at the end of the fibre optic and won’t be affected by temperature either. Our strain sensors give a valid measurement, because transverse strain doesn’t affect them. This means precise measurement is possible in the direction where the strain needs to be measured.

PES: What differentiates the WLPI fibre optic solutions from the conventional sensors, and how can it be integrated in a wind turbine?

TH: This technology makes sensors immune to EMI- Lightning, temperature and  RF. It can be used over long distance, up to 3 kilometres. These fibre optic sensors are perfectly suited for use in very harsh environments, such as cryogenic applications and under water. Our sensors are very small and easy to embed in a composite, such as a wind turbine blade and they easily resist the curing process in the autoclaves. In some applications, where heavy mechanical protection of the fibre is required, stainless steel tubing can be used and put under water. These features make it perfect for wind turbine.

PES: Why would you want to integrate optical sensors within the composite?

TH: Integration during manufacturing allows sensing, without changing the aerodynamics of the blade. We have customers that have embedded strain sensors within the blades to optimise their pitch. Some others would like to monitor material fatigue. Just imagine the possible major damage when a blade ruptures. Our sensors allow customers to monitor and optimise their wind turbine. If fatigue or
deformation occurs, the customer can stop the turbine before there is more damage. These strain sensors are also able to detect ice on the blades. There are various applications for sensor integration in the blade.

PES: Who determines the location of the sensors?

EP: Depending on the measurement needs of the customers, we advise where the sensors should be installed for optimal results. An example: one of our customers wanted to calculate the effect of ice on their wind turbine blades and so the sensors were placed accordingly. Based on the output at these key locations, they know if and where there is ice and if there is any weight unbalance. This Information is crucial to them.

PES: Can you put optical sensors on existing wind turbines that are already installed?

EP: Yes, these sensors are extremely small and can be glued or taped on blades. We have strain sensors as small as 230um.

PES: Are there more reasons why customers should use optical sensors for wind turbines?

EP: For offshore wind farms, you want reliability and the least maintenance possible. Our patented WLPI technology allows a PLUG AND FORGET solution. This means that there is no recalibration needed.  One of our customers wanted to monitor different parameters and the most important requirement was: the need of a 15 year maintenance free sensing system. He chose our solution, because we alone could fulfil this requirement. Even other optical sensing systems, such as optical sensing with a laser source, cannot match this. This feature is very important for an offshore wind farm. Another reason: this technology also allows the optical sensing device to be as far as 3 km away from the signal conditioner (reading unit), without losing accuracy in the reading. If a wind turbine is hit by lightning, our sensors won’t be affected and the fibre optic won’t carry electricity. These sensors are also good for cryogenic applications, because the strain sensors aren’t affected by the coldest temperatures from the North.

PES: Besides strain sensors, are there any other type of sensors suited for wind farms? 

TH: Yes a variety of sensors for pressure, displacement, temperature, strain, torque,  extensometers, crack meter, etc. These sensors mean that we are able to offer sensor solutions for most applications. A popular application for the wind farm is monitoring strain on the structure under water. This is done with a special strain sensor that can be spot-welded in place and under water. The fibre is normally
covered with a stainless steel sheathing, under water, in order to protect it against the elements, as well as on the surface. We can also use pressure sensors to monitor the water level in the mast. We can measure critical lubricant levels’ or simply monitor temperature. Extensometers can be used to monitor the structural integrity of both the mast and the self-supporting structure. Sensor solutions are numerous.

PES: Aside from the renewable energy market, where else does Altheris use the fibre optic sensing solutions? 

TH: As stated, fibre optic technology has many benefits and is perfectly suited for hazardous environments. These fibre optic sensor solutions are used in different branches. Our sensors are installed on equipment that goes into space and near nuclear radiation. We developed a differential pressure sensor suitable for a high tesla environment. In the Oil and Gas industry these sensors are used for pressure and temperature monitoring inside a well (SAGD) and for downhole measurement in the mining industry. But these fibre optic sensors are also used in totally different environments such as laboratories and research centres worldwide and for structural health monitoring of complex public works.

PES: Besides standard products, does Altheris also develop customised fibre optic sensor solutions?

TH: Definitely!Most of our fibre optic sensor solutions are custom made, I think about 90%. If the standard solution is not suited to our customer, we develop a customised sensor, to suit the specific need. If you are looking for a measurement solution, please contact Altheris. We love to turn every measurement challenge into a sensor solution.