Strain or temperature measurement

Measurement of strain or temperature in harsh environments often requires specialist equipment, preparations or processes, with the most common environmental challenges coming from:

• Very low or high temperature • Radioactive environments • Environments subject to high EMI • Applications subject to high fatigue • Measurements over complex forms or large areas • Multiple sensing points

Traditional electric technologies can sometimes only be used once sophisticated and expensive barriers, shielding methods or other protection is in place. As such it is rewarding to know that there is a new technology that can be used to address all the above challenging applications.

   ECN’s Fiber Optic Blade Monitoring (FOBM) strain sensor, that uses FBGS optical fiber as the measuring element. For monitoring of turbine blade root bending moments

FBGS uses draw tower technology to manufacture their fibre optic grating sensors. This results in a product that is not only mechanically stronger than traditional Fibre Bragg Gratings (>5% strain) making manual handling easier, but due to the unique composition of the glass it can be mounted on intricate structures requiring twists and turns not normally associated with optical fibre based measurement systems.

Furthermore, multiplexing many sensors on a single fibre is possible, thus reducing both the complexity and weight of the installation. As the fibre is immune to the effects of EMI, the range of possible applications where electric sensors are not suitable is vast. It has even been proven to work whilst bombarded with gamma and proton radiation and can operate effectively in temperatures from cryogenic to 200degC.

Perhaps most importantly and unlike electric strain gauged sensors, optical fibre based sensors do not require a recalibration once installed. It is possible to return to them after weeks, months or years and simply plug in an instrument to read the relative change of strain since the last visit.

Through the combination of their unique draw tower manufacturing process and the special coating material supplied exclusively by the Fraunhofer Institute for Silicate Research, FBGS optical fibre is highly suited to industrial sensing applications. The opportunities for manufacturers of sensors and transducers in industries as diverse as medical, composite, metal processing, oil & gas, weighing and wind turbines are now starting to take advantage of this.