The design and usage of the addressed combined fiber-optic sensors (ACFOSs) and the multisensory control systems of the greenhouse gas concentration on their basis are investigated herein. The main development trend of the combined fiber-optic sensors (CFOSs), which consists of the fiber Bragg grating (FBG) and the Fabry–Perot resonator (FPR), which are successively formed at the optical fiber end, is highlighted. The use of the addressed fiber Bragg structures (AFBSs) instead of the FBG in the CFOSs not only leads to the significant cheapening of the sensor system due to microwave photonics interrogating methods, but also increasing its metrological characteristics. The structural scheme of the multisensory gas concentration monitoring system is suggested. The suggested scheme allows detecting four types of greenhouse gases (СО2, NO2, CH4 and OX) depending on the material and thickness of the polymer film, which is the FPR sensitive element. The usage of the Karhunen–Loève transform (KLT), which allows separating each component contribution to the reflected spectrum according to its efficiency, is proposed. In the future, this allows determining the gas concentration at the AFBS address frequencies. The estimations show that the ACFOS design in the multisensory system allows measuring the environment temperature in the range of −60…+300 °C with an accuracy of 0.1–0.01 °C, and the gas concentration in the range of 10…90% with an accuracy of 0.1–0.5%.
Nonlinear spectrum distortions are caused by the peculiarities of the operation of charge-coupled device elements (CCD), in which the signal exposition time (Time of INTegration–TINT) is one of the significant parameters. A change of TINT on a CCD leads to a nonlinear distortion of the resulting spectrum. A nonlinear distortion of the spectrum, in turn, leads to errors in determining the central wavelength of fiber Bragg gratings (FBGs) and spectrally sensitive sensors, which, in general, negatively affects the accuracy of the measuring systems. This paper proposes an algorithm for correcting the nonlinear distortions of the spectrum obtained on a spectrum analyzer using CCD as a receiver. It is shown that preliminary calibration of the optical spectrum analyzer with subsequent mathematical processing of the signal makes it possible to make corrections in the resulting spectrum, thereby leveling the errors caused by measurements at different TINT.
A number of governing documents and by-laws of the Russian Federation, branch ministries, departments and companies have introduced the use of measuring relative air humidity, elements insulation, and SF6 into operation and maintenance process of complete switchgear. A wide range of high-precision laboratory instruments has been developed to implement these measurements. However, as a rule, these are scheduled measurements to be carried out once or twice a quarter, although the constant on-line monitoring of humidity is concerned in both the production and scientific circles of the energy industry. The possibility of on-line monitoring appeared with the advent of fiber-optic object-based passive networks for collecting information and the possibility of forming interrogation channels in them, which is provided for by the development of the Smart Grid Plus concept. Fiber optic sensors, single in their physical layer structure with passive optical networks, are highly robust and resistant to high electromagnetic fields, typical of those generated in a switchgear, and are designed to operate in harsh environments. Among their broad class, fiber optic sensors on Bragg gratings, which differ from others by direct measurement methods, have significant advantages. In particular, an increase or decrease in relative humidity will lead to a corresponding change in the wavelength of the sensing source reflected from the grating, which can be measured with an accuracy of sixth place from its absolute value.This paper proposes to consider a two-element sensor of relative humidity of a parallel structure, which differs from the existing ones by using address fiber Bragg gratings made in SMF-28 fiber. One of the gratings has a polyimide-replaced quartz shell, synthesized using a reductant fiber coating, and a completely multiplicative response to temperature and deformation caused by humidity. The second grating is recorded in a standard fiber and responds only to temperature. It is possible to include an additional third grating with a partially etched cladding, which can be used for refract metric measurements of the amount of condensed moisture on the elements of a complete switchgear. All the gratings are identical, have, as a rule, the same Bragg wavelength after manipulating their claddings, but they have differing unique addresses, which are formed by recording two transparency windows in each of the gratings with different difference frequency space. The transparency windows correspond to phase p-shifts symmetrically located at the same distance from the center of each grating. The structure obtained makes it possible to record information of the measurement conversion at the said difference frequencies in the radio range, which significantly increases the speed of relative humidity measurements and their accuracy by an order of magnitude more. In addition to what has been said, it is possible to note the capability for building a network of these sensors in series arranged in switchgear devices, with a different radiofrequency address group being used in each of them.
The article presents the solution of the actual problem of complex monitoring of external influence parameters for urban infrastructure facilities of a “smart” city. The main characteristics of fiber-optic sensors and their sensing systems are shown. Their advantages over traditional technologies for the development of monitoring directions in “smart” cities are indicated. Solutions using fiber-optic sensor networks based on quasi-distributed systems are presented.
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