FOT

Optical fiber temperature sensor is applied in the production of hot working

by:FOT     2020-07-06
Based

1 theory temperature sensor system including high temperature end doping sapphire single crystal probe, Y type quartz tracts, super bright light emitting diode ( 领导) And the drive circuit, photoelectric detector, the fluorescent signal processing system and radiation signal processing system. As shown in figure 1. In the high temperature ( More than 400 ℃) , temperature sensor based on fiber caused by heating to the principle of thermal radiation. Thermal radiation effect light emphasizes system belongs to passive temperature sensor system, it does not require additional light source, and direct black body cavity made of sapphire fiber collecting thermal radiation, and then sent to the photodiode by detection and data processing. Thermal radiation intensity and wavelength is a function of temperature. Using the black body cavity of high temperature single crystal sapphire ( α 氧化铝) Optical fiber ( Its melting point temperature of 2050 ℃) , when the black body cavity and the thermal equilibrium temperature area under test, launch and black body cavity is according to the blackbody radiation theorem under test temperature T corresponding electromagnetic radiation, the power spectrum density of emergence rate can be expressed in Plank formula for them & epsilon; λ As the spectral emissivity of the black body cavity; C1=3.74× 108 W· μ The m4 / m2 * radiation constant; C2 = 1. 44报; 102μ m· K for the second radiation constant; λ For the spectral radiant wavelength; T for the blackbody radiation temperature. This power via high temperature fiber direct coupling into the low temperature , and then into the photodiode photosensitive surface. 1 & mu; M, at the same time, in order to make the black body cavity emissivity of stability, control of the black body cavity length to diameter ratio is more than 3, so the black body cavity of spectral emissivity & epsilon; λ ≈ 1, the incident to the photodiode blackbody photosensitive surface total radiation energy for the n1, n2, respectively high temperature and at low temperature, low temperature and power between the photoelectric diode photosensitive surface coupling efficiency; 年代,l撇; α; Respectively, the high temperature fiber cross-sectional area, length, loss coefficient. In low temperature area ( Below 400 ℃) , the radiation signal is weak, the system open the light emitting diode ( 领导) , make the fluorescence test system, light emitting diode modulation of excitation light, the condenser is coupled to a branch of the Y type end, from a Y type and coupler to sapphire probe. fiber optic equipment probe end motivated excitation and emission fluorescent light, signal derived from sapphire fiber, and through the coupler from another branch of Y type end, consists of photoelectric detector. The light of the photodetector output signal after amplification by fluorescent signal processing system for processing, calculate the fluorescence lifetime get measured temperature value. 2 signal processing photodiode sensing optical radiation signal by photoelectric conversion, signal amplification, linearization, A/D conversion, the microcomputer processing temperature under test are presented. To join the multi-channel switch, in order to realize multipoint measurement through the microcomputer control, select the measuring point. As shown in figure 2. Due to is given output signal intensity is nonlinear index, the nonlinear relationship, in the digital temperature measurement, added into linear compensation device of linearization. Here choose simulate linearization, the broken line approximation scheme, which is continuous limited line instead of the curve linearization method. Characterized by simple technology, precision depends on how many line segments. 1 the probe set in the process of smelting in the process of smelting, remain the state of flow of liquid metal; Can be thought of in the temperature field, temperature in all parts of the metal liquid are basically identical. Place the probe in the solution about 10 cm below the surface, through the thermal radiation to measure temperature of the solution. 2 in the probe set in heating furnace, heat treatment furnace system of processed workpiece on the furnace wall heat transfer. Radiation heat exchange is expressed as & epsilon; 1、ε 2 the blackness of artifacts and furnace wall, respectively, & phi; 21 for Angle coefficient. When thermal equilibrium, T1 = T2, Q12 = 0. Did not have the heat exchange between, at that time the temperature of the workpiece can be measured. Put the probe in the furnace wall, external optical measure the heating temperature of workpiece. 3 temperature measurement in the process of casting solidification in the process of solidification, its temperature field for unstable temperature field. Some one in the casting section, different time, the temperature is different; At the same instant, the temperature of each point on the casting section is different also. The temperature field is coordinates ( x, y, z) And a function of time t t = ( x, y, z, t) The casting solidification process in order to measure the temperature field, temperature field and the isothermal surface change, further simulation, improve product quality and yield, it is necessary to the solidification process of multi-point measurement. fiber optic equipment temperature sensor can be fast response


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