Fiber Bragg gratings are affected by strain and temperature changes at the same time, so both factors should be considered and analyzed separately when calculating the change in reflected wavelength. When making temperature measurements, fiber Bragg gratings must remain completely unaffected by strain. You can use an fbg temperature sensor packaged specifically for this purpose, which ensures that the properties of the fiber Bragg grating inside the package are not coupled to any external bending, tensile, compressive or torsional strain. In this case, the thermal expansion coefficient αΛ of the glass is usually negligible in practice; therefore, the change in reflected wavelength due to temperature changes can be mainly determined by the temperature optical sensitivity coefficient αn of the fiber. Fiber Bragg grating strain sensors are somewhat procedurally more complex because both temperature and strain affect the reflected wavelength of the sensor. In order to make a correct measurement, it is necessary to compensate for the effect of temperature on the fiber Bragg grating during the test. To achieve this compensation, it can be done using an fbg temperature sensor in good thermal contact with the fbg strain sensor. After obtaining the test results, the second expression to the right of the plus sign can be eliminated from equation (2) by simply subtracting the wavelength change measured by the fbg temperature sensor from the wavelength change measured by the fbg strain sensor, so that This compensates for the effects of temperature changes during strain testing. The process of installing fiber Bragg grating strain sensors is similar to the process of installing traditional electrical strain sensors, and fbg strain sensors are available in many different types and installation methods, including epoxy type, weldable type, bolt-on type and Embedded type.

A typical fbg sensor will have an operating wavelength range of a few nanometers, so the optical interrogator must be able to make measurements with a resolution of a few picometers or less – a rather small order of magnitude. There are several ways to interrogate the fbg grating sensor. Interferometers are commonly used laboratory equipment that can provide fairly high resolution spectral analysis. However, these instruments are generally very expensive, bulky and not strong enough, so in some applications involving field monitoring of various structures, such as wind turbine blades, bridges, water pipes, and dams, these instruments are not used. Be applicable. A more robust approach is the introduction of charge-coupled devices (CCDs) and fixed dispersive cells, generally referred to as wavelength position switching. In this method, the fbg sensor (or series of fbg sensors) is illuminated with a broad-spectrum light source. These reflected beams will pass through a dispersive unit, and the dispersive unit will distribute the reflected beams of different wavelengths to different positions on the surface of the charge-coupled device (CCD).

By using light waves instead of electrical currents and standard optical fibers instead of copper wires as the transmission medium, fbg optical sensing addresses many of the challenges and difficulties of using electrical sensing. Both fiber optics and fbg optical sensors are insulators, have passive electrical properties, and are immune to electromagnetically induced noise. Interrogators with high optical power tunable laser sources can perform measurements over long distances with very low data loss rates or even zero loss. At the same time, unlike the electrical sensor system, one optical channel can complete the test of multiple fbg sensors at the same time, which greatly reduces the size, weight and complexity of the test system. In some applications with harsh external environmental conditions, when some commonly used electrical sensors, such as foil strain gauges, thermocouples, and vibrating wire sensors are difficult to use or even fail, optical sensors are an ideal solution. . Because optical sensors are used and mounted similarly to these traditional electrical sensors, transitioning from an electrical to an optical test solution is relatively straightforward. Having a good understanding of how fiber optics and fbg work will help you better embrace optical testing techniques and harness all the advantages this new technology has to offer.