Large-measurement-range temperature absolute value measurement method and large-measurement-range temperature absolute value measurement device

Abstract

The invention relates to the field of optical fiber temperature sensing technology, and particularly to a large-measurement-range temperature absolute value measurement method and a large-measurement-range temperature absolute value measurement device. An existing optical fiber interferometric temperature sensor has defects of incapability of measuring a temperature absolute value and small temperature measurement range. For settling the defects above, the invention discloses a large-measurement-range temperature absolute value measurement method, wherein a relationship among birefraction and length of a high-birefraction optical fiber and external temperature is utilized for establishing a relational expression T=a[phi]T+b, wherein T represents the external temperature, a and b represent undetermined coefficients, [phi]T represents a phase difference of a certain reference wavelength [lambda]0 between the fast axis and the slow axis of the high-birefraction optical fiber and furthermore satisfy a relational expression which is shown in the description, wherein B presents birefraction of the high-birefraction optical fiber, L represents the length of the high-birefraction optical fiber, [lambda]N represents a random extreme wavelength, N represents an interference grade which corresponds with the random extreme wavelength [lambda]N. In manufacture of the measurement device or before first measurement of the measurement device, interference spectrums at different temperatures are acquired for calibrating the a and b. In actual measurement, the interference spectrum in a random wavelength range is acquired, and the temperature absolute value to be measured can be calculated by means of the relational expression T=a[phi]T+b.

Description

technical field [0001] The invention relates to the technical field of optical fiber temperature sensing, in particular to a large-range temperature absolute value measurement method and a measurement device. Background technique [0002] Optical fiber temperature sensing is an important development direction in the field of sensing. It has a very wide range of applications and has unique advantages in high electromagnetic fields, high corrosion, flammable, explosive and other areas. From the perspective of temperature sensing principle, fiber optic temperature sensors include fiber grating type, fiber intensity type and fiber interference type, etc. Among them, the temperature sensitivity of fiber optic interference temperature sensor based on the principle of interference between high birefringence fiber orthogonal polarization modes can reach 1nm / °C, much higher than the fiber grating type temperature sensor, showing a very broad application prospect. [0003] The inven...

AI Technical Summary

Problems solved by technology

This method has the following disadvantages: (1) The traditional SAGNAC interferometer phase demodulation method is used for demodulation. Although this method can detect the variation of the phase difference, it cannot detect the absolute value of the phase difference, so it can only establish the phase difference The relationship between the amount of change and the amount of temperature change, so only the amount of change in temperature can be measured

(2) A long polarization-maintaining optical fiber ring is required (100-500m mentioned in the embodiment), and the cost is relatively high. The equivalent closed area surrounded by the optical fiber ring during winding is zero, and the production is difficult

This method has the following disadvantages: (1) Using the extreme wavelength detection method, the selection of the extreme wavelength is random at the initial temperature, and the interference series of different extreme wavelengths are different, so the expression The coefficient of the coefficient will also change. For each measurement, you need to select the extreme wavelength at the known calibration temperature, and then measure the temperature change through the change of the extreme wavelength. It is impossible to directly measure the absolute value of the unknown temperature value.

(2) The extremum wavelength cannot be changed arbitrarily (the coefficients corresponding to different extremum wavelengths are different), so the measurement range of this method is limited by the spectral width of the light source. When the selected extremum wavelength exceeds the spectral width of the light source, it cannot continue to monitor , which limits the temperature measurement range

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