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The working principle of a distributed fiber Raman temperature measurement system demodulator

The existing temperature measurement instruments based on Raman scattering principle use the Raman scattering effect of light to measure the temperature value inside the fiber. The temperature measuring instrument emits laser signals that propagate through optical fibers and are reflected back to the temperature measuring instrument. The temperature value of the optical fiber can be determined by the Stokes signal and anti Stokes signal in the reflected back signal.

The working principle of fiber optic demodulator

Method and device for demodulating fiber optic temperature signals, and fiber optic temperature demodulator, debugging the waveform of the current signal corresponding to the Stokes signal and anti Stokes signal to eliminate the influence of the differences between the Stokes signal and anti Stokes signal on temperature; Calculate the temperature value based on the optical flux of the debugged Stokes signal and anti Stokes signal to improve the accuracy of temperature value calculation.

When measuring the temperature value of an optical fiber, a laser signal is first emitted into the fiber at the temperature to be measured, and the laser signal propagates in the fiber. Due to the uneven structure of the amorphous material in the microscopic space of the fiber, a small part of the light will scatter. Scattered light in optical fibers includes Rayleigh scattering, Brillouin scattering, and Raman scattering. Among them, Stokes photons in Raman scattering photons and non Stokes photons carry the temperature value of the optical fiber, which is the main factor affecting the temperature resolution of the optical fiber.

Due to the fact that the reflected signals received from the optical fiber include Rayleigh scattering photon signals, Brillouin scattering photon signals, and Raman scattering photon signals. Since the spectral range of Rayleigh scattering photon signals is different from that of Brillouin scattering photon signals and Raman scattering photon signals, the received time-domain reflection signal can be subjected to Fourier transform to obtain the frequency-domain reflection signal

The fiber optic temperature demodulator includes a memory and a processor. The memory can mainly include a storage program area and a storage data area, wherein the storage program area can store an operating system, at least one application program required for a function, etc; The storage data area can store data created based on usage, etc. In addition, the memory may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device. Used to run computer programs stored in the memory to enable the fiber optic temperature demodulator to perform fiber optic temperature signal demodulation methods or the functions of various modules in the fiber optic temperature signal demodulation device.

Distributed fiber optic sensing technology

In distributed fiber optic sensing technology, it can be divided into distributed fiber optic sensing systems based on Rayleigh scattering, distributed fiber optic sensing systems based on Brillouin scattering, and distributed fiber optic sensing systems based on Raman scattering according to the type of backscattering of the fiber optic. Distributed fiber optic sensing systems based on Rayleigh scattering are mostly used for fault point detection in optical fibers. The distributed fiber optic sensing technology based on Raman scattering is only applied to temperature monitoring along the fiber optic line.

Distributed Fiber Raman Temperature Measurement System

The distributed fiber Raman temperature measurement system utilizes the spontaneous Raman scattering effect in the fiber and combines optical time domain reflection technology, OTDR is a new type of sensing system that can be used for distributed, continuous, and real-time measurement of spatial temperature field distribution. Compared with traditional electronic temperature sensors, distributed fiber Raman temperature measurement systems have advantages such as resistance to electromagnetic interference, high voltage, high accuracy, and simple structure. Therefore, they are widely used in fields such as power cable temperature monitoring, structural health monitoring, and dam leakage monitoring. In the distributed fiber Raman temperature measurement system, temperature demodulation method is the most effective way for the system to detect temperature along the light path
Key technologies. The commonly used temperature demodulation method currently uses anti Stokes light as the signal channel and Stokes light as the reference channel. By demodulating the anti Stokes Raman scattering optical time-domain curve of the fiber through the fiber’s Stokes Raman scattering optical time-domain curve, the temperature information at any point along the fiber is demodulated.

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