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Fiber Bragg grating strain measurement technology for transmission towers

The safety monitoring technology of major power facilities such as transmission towers has been highly valued, and the deformation status of key parts in harsh environments such as typhoons and icing has been a concern for researchers. The traditional electrical measurement technology has obvious limitations in application due to its susceptibility to electromagnetic interference in the transmission environment, natural lightning strikes, and other practical problems. Fiber optic sensing, which uses light as a signal and is not affected by electromagnetic interference, provides excellent technical support for sensing, detection, and monitoring in the power environment. Distributed fiber optic and fiber optic grating technologies are gradually being applied in power facility safety monitoring. Among all monitoring parameters, strain is the most fundamental and important. It is the most fundamental reflection of various deformations such as bending, torsion, and displacement. Therefore, effective strain sensing and detection technology based on fiber optic principles has always been a focus of attention for researchers. Fiber Bragg grating, as a type of fiber optic sensing, adopts wavelength encoding, and the wavelength signal is not affected by power fluctuations of the light source. Different wavelengths of gratings can be reused on a single fiber, which is very sensitive to axial strain and plays an important role in strain measurement of major power facilities.

At present, there are mainly two types of strain measurement technologies based on fiber Bragg gratings: one is to directly paste or embed the bare grating onto the surface or inside of the tested object using adhesive. This method appears to have simple and convenient operation steps on the surface, but in engineering practice, due to the fragility of the bare grating, it is difficult to accurately control the straightness and direction of the grating layout when pasting in the field or other fields, and the bare grating is prone to breakage. Therefore, this method is more suitable for conducting scientific research testing in laboratories, and has poor adaptability in engineering sites. Secondly, encapsulating fiber Bragg gratings in specially designed elastomers or substrates provides protection for the gratings and improves operability when installed on the tested object. When using this method to package gratings, there are mainly two ways to fix the gratings – pasting and fixing all the grating areas and fixing the fibers on both sides of the pre stretched grating area. There are three main types of packaging substrates – tubular structure, surface elastic structure, and substrate structure. Fiber Bragg Grating is packaged into a tubular strain gauge body and is generally used for embedding in the measured object to measure concrete strain, bridge deformation, etc. During surface strain testing, fiber Bragg gratings are often encapsulated in specially designed surface mounted elastic structures, and flexible hinge structures are often used to achieve flexible design of strain sensitivity for fiber Bragg gratings.

In the above two structures, fiber Bragg gratings are generally packaged using pre stretched fiber fixed on both sides of the grating area. Although it can ensure that the grating is not prone to chirping, the measurement range of negative strain of the tested object is easily limited due to the limited pre stretching amount. In addition, during installation, it is often necessary to drill holes on the tested object, which can easily damage the structural strength of the body. Another method is to encapsulate the fiber optic grating in the substrate by pasting and fixing it through the grating area. The fiber optic grating can be stretched or compressed as the measured object is as a whole, and the strain measurement range is larger. It can be directly pasted on the measured object without changing the structure of the measured body.



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