Optical Fiber Temperature Sensor System Research Articles

Dual-mode optical thermometers via the thermochromic Bi3+, Eu3+ co-doped La2LiSbO6 phosphors for real-time chip temperature monitoring

In recent years, with the increasing demand for non-contact temperature measurement, it is urgent to develop a new type of phosphor with double emission centers, high sensitivity and good reliability. A series of Bi3+and Eu3+ co-doped La2LiSbO6 double emission center phosphors were successfully prepared. The response characteristics of Bi3+and Eu3+ at different temperatures in the range of 293–473k were calculated by fluorescence intensity ratio (FIR) technique. The optimal relative sensitivity Sr and absolute sensitivity Sa were 1.13 % K−1 and 1.27 % K−1, respectively. Hence, La2LiSbO6:Bi3+, Eu3+ phosphors have the capability of non-contact optical temperature measurement and are a promising material for application. The phosphor is combined with the optical fiber temperature sensor to monitor the real-time temperature of the computer central processing unit. The optical fiber temperature sensor system breaks through the limitations of traditional temperature measurement, and can be used in special environments such as small size and strong electromagnetic interference. It has become an ideal choice to replace the traditional temperature sensor.

Fiber Optic Temperature Sensor System Using Air-Filled Fabry-Pérot Cavity with Variable Pressure.

We report a high-resolution fiber optic temperature sensor system based on an air-filled Fabry-Pérot (FP) cavity, whose spectral fringes shift due to a precise pressure variation in the cavity. The absolute temperature can be deduced from the spectral shift and the pressure variation. For fabrication, a fused-silica tube is spliced with a single-mode fiber at one end and a side-hole fiber at the other to form the FP cavity. The pressure in the cavity can be changed by passing air through the side-hole fiber, causing the spectral shift. We analyzed the effect of sensor wavelength resolution and pressure fluctuation on the temperature measurement resolution. A computer-controlled pressure system and sensor interrogation system were developed with miniaturized instruments for the system operation. Experimental results show that the sensor had a high wavelength resolution (<0.2 pm) with minimal pressure fluctuation (~0.015 kPa), resulting in high-resolution (±0.32 ℃) temperature measurement. It shows good stability from the thermal cycle testing with the maximum testing temperature reaching 800 ℃.

A Photon-Counting Optical Time-Domain Reflectometry Based Optical Fiber Temperature Sensor System

A photon-counting optical time-domain reflectometry (PC-OTDR) based optical fiber temperature sensor system is proposed and demonstrated experimentally in this work. In the system, a high speed photon-counting module is developed for fast measurement and a cascade SMF (single- mode fiber)-COF (capillary optical fiber)-SMF fiber structure is designed for the temperature sensing. Thanks to the newly developed active quench and reset integrated circuits, the photon-counting module achieves a maximum counting rate of nearly 35 Mcounts/s that allows the PC-OTDR based optical fiber sensor system achieving the OTDR trace of a 20 m fiber-under-test (FUT) within 0.2 ms and a 6 km FUT within 20 s. The spatial resolution measured is about 3.8 cm and 60 cm for the FUT of 20 m and 6 km respectively. To test the system's optical sensing usefulness, a SMF-COF-SMF is developed and connected to the FUT of the system to form a temperature sensor. The COF is filled by UV glue whose refractive index is sensitive to the temperature. Experimental results show that this system is capable of measuring the temperature in the range from 20 °C (room temperature) to 220 °C, which can also locate the sensing position accurately.

Distributed fiber optic temperature sensor based on dynamic calibration of Raman Stokes backscattering light intensity

In a distributed fiber optic temperature sensing system, the intensity of Raman Stokes backscattering light serving as reference light increases with the increase of temperature, leading to measurement errors in the system. A novel method of dynamically calibrating Raman Stokes backscattering light intensity is proposed to improve temperature accuracy for distributed fiber optic temperature sensors. According to the real-time Stokes intensity distribution in the reference fiber, Stokes intensity curve of the whole fiber at a reference temperature is simulated, and the temperature response of Stokes light is corrected. The ratio of Raman anti-Stokes light intensity to the calculated Stokes light intensity is used to demodulate temperature along the fiber. The experimental results indicate that the temperature accuracy of the distributed optical fiber temperature sensor system after making the Stokes optical dynamic calibration is increased up to 4.3 ℃ compared with that from the conventional method. And the accuracy of temperature measurement is improved by 8.9 ℃ when combined with Rayleigh noise suppression method. This study provides a new solution for a distributed fiber optic temperature sensor system to monitor high temperature environment temperature.

Multi-channel fiber-optic temperature sensor system using an optical time-domain reflectometer

Abstract In this study, we developed a multi-channel fiber-optic temperature sensor system (FTSS) using an optical time-domain reflectometer (OTDR). The developed FTSS consists of fiber-optic temperature-sensing probes, a fiber-optic coupler, a transmitting optical fiber, and an OTDR. The fiber-optic temperature-sensing probes comprise silicon oil, a nickel-plated brass cap, a fiber channel (FC) terminator, and a single-mode optical fiber. The developed FTSS has four channels, which have fiber-optic temperature-sensing probes, connected using single-mode optical fibers of different lengths. Silicon oil is employed as a temperature-sensing material, as its refractive index changes with the temperature variations. We measured the optical powers of the reflected light signals (Fresnel reflection), which are generated at the interface between the silicon oil and core of the single-mode optical fiber in the distal ends of the sensing probes. The optical powers of the four channels of the FTSS were measured to simultaneously determine individual temperatures at four different points using an OTDR.

Experimental study on distributed optical fiber heated-based seepage behavior identification in hydraulic engineering

The theoretical analysis and physical experiment on seepage behavior identification with distributed optical fiber temperature sensor system (DTS) are implemented. The distributed optical fiber-based approaches monitoring the seepage velocity and phreatic line in embankment dam or dike engineering are proposed. Firstly, the physical heat transfer process between optical fiber and porous material is analyzed. The basic principle identifying seepage behavior according to optical fiber temperature is presented. Secondly, a DTS-based test platform identifying seepage behavior in embankment dam or dike engineering is developed. Thirdly, the heat transfer coefficient in heat transfer theory is adopted to describe the heat transfer between optical fiber and saturated porous material. The experimental analysis for the relationship between overall heat transfer coefficient (i.e., the ratio of heating power and temperature rise) and seepage velocity is implemented. The mathematical model representing above relationship is built and an empirical method is given to monitor the seepage velocity in hydraulic engineering. Fourthly, the effect of moisture content on optical fiber temperature rise is analyzed by the experiment. The optical fiber arrangement plan is designed to monitor the phreatic line in embankment dam or dike engineering, the method is proposed to determine the position of phreatic line.

Experimental study on distributed optical fiber-based approach monitoring saturation line in levee engineering

Seepage is one of key factors which affect the levee engineering safety. The seepage danger without timely detection and rapid response may likely lead to severe accidents such as seepage failure, slope instability, and even levee break. More than 90 percent of levee break events are caused by the seepage. It is very important for seepage behavior identification to determine accurately saturation line in levee engineering. Furthermore, the location of saturation line has a major impact on slope stability in levee engineering. Considering the structure characteristics and service condition of levee engineering, the distributed optical fiber sensing technology is introduced to implement the real-time observation of saturation line in levee engineering. The distributed optical fiber temperature sensor system (DTS)-based monitoring principle of saturation line in levee engineering is investigated. An experimental platform, which consists of DTS, heating system, water-supply system, auxiliary analysis system and levee model, is designed and constructed. The monitoring experiment of saturation line in levee model is implemented on this platform. According to the experimental results, the numerical relationship between moisture content and thermal conductivity in porous medium is identified. A line heat source-based distributed optical fiber method obtaining the thermal conductivity in porous medium is developed. A DTS-based approach is proposed to monitor the saturation line in levee engineering. The embedment pattern of optical fiber for monitoring saturation line is presented.

Monitoring water seepage velocity in dikes using distributed optical fiber temperature sensors

Abstract Seepage in dike engineering, especially its soil-concrete joint, is one of influencing factors of dike safety. Most of disastrous accidents of dike engineering are induced directly or indirectly by seepage. The reliable observation and reasonable identification of seepage behavior play an important role in ensuring the service safety of dike engineering. In this paper, a distributed optical fiber temperature sensor system (DTS)-based approach is presented to monitor the seepage velocity in soil-concrete joint between dike structure and other constructions across it such as culvert and sluice. The theoretical investigation and laboratory test are carried out. Firstly, the DTS-based monitoring principle of seepage velocity is introduced. The theoretical model identifying seepage velocity is established. Secondly, a DTS-based test platform of soil-concrete joint, which can simulate the structural feature and service environment of dike engineering, is designed and constructed. It consists of DTS, heating system, water-supply system, data processing system and dike model. Thirdly, the monitoring experiments on seepage velocity under the conditions of different mediums and optical fibers are implemented using the test platform. The correlations between seepage velocity and heating power, temperature change of optical fiber are analyzed. The practical model monitoring seepage velocity of soil-concrete joint in dike engineering is built. Lastly, considering the seepage features of dike engineering, the embedment mode and procedure of optical fiber are proposed to promote the application of DTS-based approach to real-time observation of seepage velocity in actual dike engineering.

Design of distributed Raman temperature sensing system based on single-mode optical fiber

The distributed optical fiber temperature sensor system based on Raman scattering has developed rapidly since it was invented in 1970s. The optical wavelengths used in most of the distributed temperature optical fiber sensor system based on the Raman scattering are around from 840 to 1330 nm, and the system operates with multimode optical fibers. However, this wavelength range is not suitable for long-distance transmission due to the high attenuation and dispersion of the transmission optical fiber. A novel distributed optical fiber Raman temperature sensor system based on standard single-mode optical fiber is proposed. The system employs the wavelength of 1550 nm as the probe light and the standard communication optical fiber as the sensing medium to increase the sensing distance. This system mainly includes three modules: the probe light transmitting module, the light magnifying and transmission module, and the signal acquisition module.

Fabry-Perot ITU 필터의 기준파장을 이용한 분배형 광섬유 격자 온도센서의 선형복조

15개의 광섬유 격자를 이용하여 전력설비의 온도변화를 상시 감시하는 분배형 광섬유 온도센서 시스템을 제작하였다. MEMS 파장가변 필터를 사용하는 복조시스템의 비선형 동작특성에 의한 측정오차를 보상하기 위하여 Fabry-Perot ITU 필터의 투과파장을 기준으로 하는 다항식 피팅 알고리즘을 사용하였다. 실험을 통하여 보상알고리즘이 구동주파수와 무관하게 센서시스템의 정밀도를 유지하는 것을 확인하였으며 기준 온도계로 사용한 써모커플과의 선형화 오차는 약 0.18[%]로 측정되었다.

전력설비 보호를 위한 분배형 광섬유 온도센서

전력설비의 비정상적인 온도변화를 감시할 목적으로 10개의 광섬유격자를 이용하여 1[℃] 이내의 온도분해능을 가지는 준분배형 광섬유 온도센서를 제작하였다. 파장가변 FP 필터를 스캔하여 얻어지는 PD 출력파형의 피크위치를 검색하여 광섬유격자 센서의 출력변화를 읽어내었고, 가우시안 line-fitting 알고리즘으로 광섬유격자의 반사스펙트럼 왜곡에 의한 영향을 보상하고 정밀도를 향상시켰다. 제작한 센서시스템과 기준 온도계로 사용한 thermocouple 간의 측정값 오차는 1[%] 이내이며, 선형화 오차는 약 0.37[%]으로 측정되었다.

Time- and frequency-domain analyses of fluorescence lifetime for temperature sensing

Fluorescence lifetime detection is widely used for sensing physical and chemical quantities. The measurement accuracy of fluorescence lifetime-based sensing systems, either in time or frequency domain relies on their capability of detection and analysis of low level signal superimposed to noise. In this work a quantitative assessment of several data processing and analysis methods for the estimation of the fluorescence lifetime was carried out by using an experimental arrangement based on a fiber optic temperature sensor system. A comparison between the various methods was performed using actual signals from an optical sensing medium. The basic principles of time- and frequency-domain lifetime measurements were also reviewed and discussed in order to point out the limit of the cw frequency-domain approach and to suggest a way to overcome it. The investigated lifetime interval was from 200 to about 2200μs, corresponding to a temperature span of the sensor of about 300 °C. The results showed that in time domain (such as with Marquardt, integration, and log-fit algorithms) a good agreement, with relative differences from 0.2% to 0.5%, can be reached. Frequency-domain results based on an N-point fast Fourier transform (FFT) compare favorably with the previous ones in the long lifetime region (resulting in relative differences lower than 0.2%) with larger differences for short lifetimes. For each data processing method, the uncertainty associated with lifetime estimation was evaluated. Sampling and harmonics effects on the estimation accuracy for N-point FFTs were also investigated to trade-off between speed and accuracy of the algorithm in view of its application in real-time detection systems.

An enhanced fiber-optic temperature sensor system for power transformer monitoring

The paper deals with a sensor for temperature measurements in fluids. The sensor is based on a fiber-optic sensing element and on microcontroller-based signal processing hardware. The physical principle behind its operation is briefly reviewed, and its application to power transformer hot-spot temperature measurement is reported. Laboratory experimental results are given for both sensor characterization and measurements carried out on a 25-kVA oil-cooled power transformer.

Erbium/ytterbium fluorescence based fiber optic temperature sensor system

Erbium/ytterbium co-doped fibers have been investigated in this work for the first time to determine their potential in thermometry applications based on the use of fluorescence decay. Several samples have been used and their performance characteristics determined. These have included studies of fiber annealing as well as thermal cycling tests and it was found that unlike other rare-earth ion doped fibers previously studied, such as Nd3+, Er3+, or Tm3+ doped fibers, the Er/Yb co-doped samples used here have shown a much smaller degree of thermal annealing when their thermal characteristics have been evaluated and compared. The response of the thermometer and the error in the measurement was found to be, at &amp;lt;±5 °C, within the stability of the oven used in the tests over a wide temperature range from 0 to 850 °C.

Quasidistributed fluorescence-based optical fiber temperature sensor system

The use of multiple material fluorescence-based sensors, where each is optimized to a particular temperature range yet is pumped by the same light source, emitting over the same spectral region, makes for a very simple, convenient and promising optical arrangement which can be applied in real-time, quasidistributed temperature sensor systems. The fluorescence lifetime approach, which is an important technique to enable fluorescence emission to be exploited for thermometry, is adopted in the system discussed. An analysis scheme using Prony’s method has been reported which enables exponential decays from either single-material or two material and quasidistributed sensors to be deconvolved and thus data and associated measurand information encoded in each individual signal to be recovered. In this work, in the development of quasidistributed temperature sensor algorithms based on Prony’s method are used for the estimation of exponential time constants of a convolved triple exponential fluorescence decay, each corresponding to a different-point temperature. Experimental results obtained are presented to justify their use in practical multiexponential fluorescence decay analysis and show a comparison of the Prony method to the Marquardt nonlinear least-squares approximation algorithm to achieve the deconvolution. The computational time for Prony’s approach is approximately one-thousandth that of the Marquardt technique while the accuracy achieved using Prony’s method is still high enough for practical use.