Fiber optic temperature sensor, Intelligent monitoring system, Distributed fiber optic manufacturer in China
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Fiber optic grating sensors can measure temperature or strain, with advantages such as small size, high sensitivity, intrinsic safety, anti electromagnetic interference, quasi distributed measurement, mass production, and easy networking. They have been widely used in fields such as fire monitoring, structural health monitoring, and petrochemical safety monitoring.
The working principle of fiber optic grating demodulator
It is also known as a fiber Bragg grating instrument or fiber Bragg grating signal processor within the company. Its working principle is roughly as follows: the instrument outputs a specific optical signal to the optical path with sensors. When there is a certain change in the detected amount (such as temperature) outside the sensor (such as a certain degree of temperature increase), the optical characteristics of the corresponding sensor will also change, causing certain parameters of the optical signal reflected back from the sensor to the instrument to change accordingly. At this time, the instrument will process the received optical signal and compare it with the pre-set threshold. Once it exceeds the set range, the instrument will immediately respond or activate the alarm. Or upload data, etc.
The spatial distribution period of the refractive index of fiber Bragg gratings varies with external factors such as temperature and strain, causing the center wavelength of reflected light to shift. Therefore, wavelength demodulation method is mainly used for demodulation of fiber Bragg gratings. At present, the main demodulation methods for fiber optic grating sensors include: unbalanced Mach Zehnder interferometry demodulation, spectral analyzer demodulation, tunable filter demodulation, and scanning laser demodulation. The unbalanced Mach Zehnder interferometer demodulation method uses Mach Zehnder interferometers with different arm lengths to convert the wavelength change of the reflected light from the fiber optic grating sensor into the phase difference change between the output light of the reference arm and the output light of the measurement arm. By measuring the phase difference, the wavelength drift of the fiber optic grating can be determined. This demodulation method has high sensitivity and resolution, but the interferometer itself is easily affected by external factors such as temperature and vibration, resulting in significant errors. The essence of spectral analyzer demodulation method, tunable filter demodulation method, and scanning laser demodulation method is to obtain the spectrum of grating reflected light through dispersion spectroscopy or wavelength scanning, calculate the corresponding wavelength of the peak through peak finding algorithm, and then demodulate the temperature or strain based on the calibrated linear equation. These wavelength demodulation methods based on spectral measurement have advantages such as high demodulation accuracy, unaffected by changes in light source power and optical path loss, and the ability to achieve quasi distributed multiplexing measurement. They are currently the mainstream demodulation technology for fiber optic grating sensors in engineering applications.
The internal light source module of the fiber optic grating demodulation host sends optical signals to the fiber optic grating sensor through an optical cable. The fiber optic grating sensor then reflects the real-time information collected to the fiber optic grating demodulation host and performs demodulation processing to obtain the temperature and strain information collected by the sensor. The fiber optic grating demodulation host can display and store monitoring data. When the monitored value exceeds the limit, the host can output over temperature alarm and over strain alarm signals to inform relevant maintenance personnel to go to the fault location for timely repair and handling.
The main functions of the fiber optic grating tunnel monitoring system are:
(1) Tunnel temperature monitoring, fast, accurate, and real-time measurement of temperature changes inside the tunnel, and alarm in case of abnormalities;
(2) Tunnel structure monitoring, real-time measurement of the compression and deformation of the tunnel inner wall, and alarm in case of abnormalities;
(3) Analysis of changes in track structure to prevent safety accidents from occurring;
(4) Alarm function, based on the set temperature, strain (pressure) alarm threshold values of each monitoring point, to make real-time judgments and alarms;
(5) Display function for graphical annotation display;
(6) The data storage and playback function allows for playback and analysis of recorded data when historical information tracing is required;
(7) Support multiple data upload methods.
The tunnel monitoring system using fiber optic gratings has the following characteristics:
(1) High sensitivity, and due to the characteristics of the optical fiber itself, there is basically no loss in the transmission process of the measured signal, and it is also basically not affected by external signal interference, thus achieving high sensitivity.
(2) There are multiple sensing parameters, and sensors can be made on a single optical fiber to sense different physical quantities.
(3) Strong adaptability, using optical fiber as the medium and sensing element for signal transmission, it can resist electromagnetic interference, lightning strike, waterproof and moisture-proof, and has stable chemical properties such as high and low temperature resistance, water and fire resistance, high pressure resistance, and corrosion resistance. Suitable for measurement in harsh environments such as prolonged humidity, high temperature, flammability, perishability, explosiveness, and strong electromagnetic interference.
(4) Good safety, fiber optic sensors have inherent safety characteristics. Therefore, when used in measurement, there are no safety hazards such as leakage and electric shock.
(5) It has a long service life and stronger durability compared to traditional sensors.
