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Measurement accuracy and spatial resolution of a distributed temperature sensor based on a two-pulse differential coherent reflectometer
We present a model and numerical simulation of a distributed temperature sensor based on a two-pulse differential coherent optical time-domain reflectometer (COTDR). The differential phase measured using a phase-sensitive Rayleigh reflectometer is shown to have a regular component, which is a linear function of temperature, and a random component, which is related to a random distribution of scattering centres in the fibre and restricts the accuracy of measurements of variations in temperature. Measurement accuracy can be improved by reducing the relative contribution of the random component via a decrease in pulse duration and/or an increase in the time delay between pulses. The spatial resolution of a differential two-pulse phase-sensitive reflectometer is shown to be determined by the time delay between pulses and to vary little with pulse duration. At a typical pulse duration (200 ns) and delay time (300 ns), the accuracy in measurements of variations in temperature in the 0.1-K range is 2 % and the spatial resolution is about 30 m. (fibre-optic sensors)
High-Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors
The goal of this work was to investigate the in-core performance of sapphire optical fiber temperature sensors and to develop clad sapphire optical fibers for in-core instrumentation. We fabricated clad sapphire optical fibers and evaluated the distributed sensing performance of these sensors via optical backscatter reflectometry under high fluence and combined radiation and temperature effects. A series of irradiations was completed to evaluate the effect of irradiation on sapphire optical fiber temperature sensors and to determine the operational limits of these sensors. (1) Objective 1: Fabricate sapphire optical fiber sensors. (2) Objective 2: Evaluate the clad sapphire fiber to verify single-mode behavior and determine and characterize the light modes supported by optical fibers. (3) Objective 3: Characterize the in-core temperature sensing of sapphire optical fiber, as well as the combined temperature and irradiation effects. (4) Objective 4: Evaluate the lifetime and performance of the sensor under irradiation to high neutron fluence. Objectives 1, 2, and 3 were completed during the first 2 years of the project. Due to the Covid pandemic, Objective 4, a high-fluence irradiation performed at the Massachusetts Institute of Technology Research Reactor (MITR), was delayed, as partner facilities were subject to mandatory shutdowns and required a 1 year, no-cost extension. This irradiation was eventually completed on December 12, 2022. This work indicates that sapphire optical fiber sensors may be a solution for ultra-high-temperature applications in which traditional silica optical fibers are prone to fail. Sapphire sensors are potentially suitable for experiments featuring temperatures above 700°C for long periods of time, or for any length of time above 1000°C. Experiments featuring a low total fluence, such as irradiations conducted in the Transient Reactor Test (TREAT) facility, also represent good applications for sapphire optical sensors. Additional work is required to characterize the sapphire fiber cladding performance, which falls outside the scope of this project, as well as the effects of high temperatures on the response of the fiber. A comprehensive material study is recommended as future work to evaluate the attenuation in sapphire under irradiation, and how that attenuation changes with irradiation temperature. The drift and attenuation in the fiber at temperatures of up to 1600°C and a total fluence of up to 2.9 x 10 17 n/cm 2 was minimal, and the fibers returned to baseline after being heated to 1600°C under irradiation. This is promising for the future use of sapphire optical fibers in advanced reactors.
High Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors
Investigate the in-pile performance of sapphire optical fiber temperature sensors and to develop clad sapphire optical fibers for in-pile instrumentation. Evaluate the distributed sensing performance of the sensors through optical backscatter reflectometry under combined radiation and temperature effects, and high fluence.
Low-Cost Distributed Temperature Sensor Using Electrical TDR DOE SBIR Phase 1 Final Technical Report
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Calibration of Distributed Temperature Sensors Using Commercially Available SMF-28 Optical Fiber From 22 °C to 1000 °C
Optical frequency domain reflectometry (OFDR) is a family of optical techniques which can be used to produce distributed temperature measurements from the spectral shift of an interference pattern based on the Rayleigh backscatter signature of an optical fiber. Adaptive signal processing techniques have recently been used with OFDR to record meaningful spectral shift data from commercially available SMF-28 optical fibers heated beyond 950 °C. Furthermore, a correlation between the measured spectral shift and temperature has not yet been developed at these high temperatures. To extend the measurable temperature range of OFDR in SMF-28, this work describes the development of such a correlation from room temperature (22 °C) to 1000 °C. The relationship between spectral shift and temperature change over this range was found to be best characterized by the fourth-order polynomial ΔT=(-4.241 * 10 -11 )S 4 + (-2.017 * 10 -7 )S 3 + (-3.677 * 10 -4 )S 2 + (-0.8057)S, where ΔT represents the temperature difference compared to the reference temperature, and S represents the spectral shift measured by the fibers. The calibration developed in this work assumes that the fiber has been fully annealed by heating the fiber to 1000 °C for a few hours. This paper is the first to demonstrate the calibration and use of SMF-28 distributed optical fiber sensors up to 1000 °C, enabled using adaptive OFDR-based signal processing.
High-Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors - ASI Project Summary
The goal of this work is to investigate the performance of sapphire optical fiber temperature sensors and develop clad sapphire optical fibers for in-pile instrumentation. This work tests the distributed sensing performance of sapphire sensors by using optical backscatter reflectometry methods under combined radiation/temperature effects and high fluence. A series of irradiations will be completed to evaluate the effect of irradiation on sapphire optical fiber temperature sensors and to determine an operational limit for the sensors.
High Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors [Slides]
All objectives have been completed. Heated irradiation indicates potential for sapphire fiber-based sensors to be used in extreme environments beyond silica fiber temperature limits. Sapphire optical fiber may not be appropriate for high fluence applications. Clad sapphire optical fibers have a temperature-dependent attenuation that has not been observed in unclad sapphire. With the appropriate pre-treatments and data post-processing, sapphire optical fiber has the potential to serve as a distributed sensor up to 1700ºC.
Fiber optic distributed temperature sensor mapping of a jet-mixing flow field
Not Available
High Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors
No Abstract, slides Only
High Fluence Active Irradiation and Combined Effects Testing of Sapphire Optical Fiber Distributed Temperature Sensors
NA: This is a yearly progress summary presentation describing progress to date on an NSUF funded irradiation test series meant to evaluate the performance of sapphire optical fiber sensors.
High-resolution wall temperature measurements with distributed fiber optic sensors
Conventional approaches of surface temperature measurement are often unreliable, and other methods may not be practical in closed, high-temperature spaces. In this study, surface temperature measurements of the cooling panel of a natural circulation facility were performed with fiber optic distributed temperature sensors (DTS). High resolution surface temperature profiles of the cooling panel were acquired under two steady experimental conditions, and compared with measurements performed with nearby thermocouples. The total measurement error of the DTS results presented has been estimated to be ±4.4 °C. The findings reflected herein show that these DTS can reasonably measure surface temperature when installed with the methods developed in this study. Through the analysis of the DTS data collected, the interesting behavior of the cooling panel was revealed, providing new insights on the system's behavior that may be beneficial to the design and optimization of such heat transfer devices. These sensors can also provide the measurement density necessary for validation efforts with highly-resolved prediction methods such as finite element analysis (FEA) or computational fluid dynamics (CFD).
Distributed Temperature Monitoring of Tundish Refractory Lining Using Optical Fiber Sensors
Distributed temperature monitoring can provide useful insights into the thermal conditions in the continuous caster tundish that can affect operating stability and cast quality, such as preheat conditions, superheat uniformity, fill height, and refractory wear. In the current study, fiber optic sensors were embedded into the refractory lining of a lab-scale tundish to record the temperature profiles during dry-out, preheating, and direct molten steel exposure to demonstrate sensor performance. Additional trials were performed with fiber optic sensors embedded in an industrial tundish used in production. Furthermore, the results demonstrate that fiber optic sensors using Rayleigh technology can provide accurate distributed temperature measurements in refractory lined vessels and provide useful information about the process.
Evaluation of Fiber Bragg Grating and Distributed Optical Fiber Temperature Sensors
Fiber optic temperature sensors were evaluated in the High Temperature Test Lab (HTTL) to determine the accuracy of the measurements at various temperatures. A distributed temperature sensor was evaluated up to 550C and a fiber Bragg grating sensor was evaluated up to 750C. HTTL measurements indicate that there is a drift in fiber Bragg sensor over time of approximately -10C with higher accuracy at temperatures above 300C. The distributed sensor produced some bad data points at and above 500C but produced measurements with less than 2% error at increasing temperatures up to 400C
Experimental study on the startup of the annular wick type heat pipe using fiber optical temperature measurement technique
This study used optical fiber-distributed temperature sensors to measure the internal and external temperature distributions of a water-cooled heat pipe. The sensor technology used in this study is fiber optical distributed temperature sensing, a distributed sensing technique based on the naturally occurring Rayleigh backscatter in optical fibers. This measurement technique provides maximum spatial resolution for static and semi-static applications. Using this sensor, the temperature distribution of the heat pipe's internal, external, vapor core, and the wick was measured with a spatial resolution of 0.65 mm, a sampling frequency of 40 Hz, and a temperature resolution of 0.1 °C. Through the measured temperature distribution database, the starting phenomenon, the effective length trend, and the limitation onset were observed. From the results, it is found that a high-temperature peak appears at the evaporator if a high initial power (75 W) is imposed on the heat pipe, even after the heat pipe approaches the normal operating status. The peak is not observed in a slower startup (30 W initial power then slowly increased to 75 W). It is also found that the temperature distributions and effective condenser length of the heat pipe highly depend on the cooling conditions. There are variations in the temperature according to the radial direction of the horizontal heat pipe due to gravity. In conclusion, lead and lag of the temperature evolution were observed at the onset of the operating limitations.
Robust metal-ceramic coaxial cable sensors for distributed temperature monitoring in fossil energy power systems
The project aims to develop a new type of low cost, robust metal-ceramic coaxial cable (MCCC) Fabry-Pérot interferometer (FPI) sensor and demonstrate the capability of cascading a series of FPI sensing points in a single MCCC for real-time distributed monitoring of temperature up to 1000°C. The technical accomplishments of this project include: (i) development of metal and ceramic materials for fabricating the MCCC suitable for use in high temperature (up to 1000oC) fossil fuel, (ii) design, construction and test of single point MCCC-FPI sensors for high temperature measurement at deviation within ±2.7%, (iv) demonstration of the MCCC-FPI sensors for real-time distributed temperature measurement with desired sensitivity, spatial resolution, stability, and response speed that are important to practical applications, and (v) development of a novel MCCC-FPI sensor platform for measuring high frequency dielectric constants for solids and liquids as function of temperature. Single point MCCC-FPI sensors are fabricated based on the FPI parameters, including the relationship between reflector width and reflectance as well as the inter-reflector distance for a FPI, estimated by model calculations. MCCC-FPI sensors have been made using insulators of packed ceramic powders, ceramic tubes, and air or inert gases; outer conductors of various metal tubes; inner conductors of wires of the same metal materials as the tubes used; and reflectors of dense ceramic discs, casted ceramic discs and air gaps. The insulator, conductor and reflector materials are investigated for their thermal, chemical, and structural stabilities under temperatures up to 1000°C in simulated coal-derived syngas. Based on the experimental findings, alumina tube and discs, and stainless steel tube and wire are selected for reflector, insulator and outer and inner conductors, respectively. Air or inert gases are found to be useful for reflectors (in the form of narrow groves) or insulators (in the form of empty chamber cavity between ceramic discs) in construction of MCCC-FPI sensors. Single point MCCC-FPI sensors have been fabricated using stainless steel as conductors, dense α-alumina tubes as dielectric insulators, and two air gaps in the insulator as reflectors. The MCCC-FPI sensor with air gap reflectors has been demonstrated for measuring temperature between 200 and 500°C using microwave as sensing signal in a frequency range of 2 – 8 GHz. The temperature measurement is achieved by monitoring the frequency shift (Δƒ) of a selected resonant peak of the microwave interferogram reflected from the pair of air gap reflectors. The MCCC-FPI sensor exhibited excellent linear temperature-dependence for Δƒ, good accuracy (deviation ±2.7%), and reasonable response speed (<180 s for stabilization). Thermal drifting of the sensing signal was also rather minimal for the MCCC-FPI sensors after operating for more than one week at around 500oC. MCCC-FPI sensors with each containing 2 or 3 pairs of reflectors (i.e. 2 or 3 FPIs in a single cable) have been fabricated and demonstrated for distributed temperature measurement between 250 and 550°C in a microwave frequency range of 3-6 GHz. The measurement is achieved by monitoring the frequency shift of a selected resonant peak of the reflected microwave interferogram, which is obtained by the join-time-domain signal processing method. The results demonstrate that the FPI sensing points in both the three-point and two-point MCCC sensors can measure distributed high temperature with good reproducibility and consistency in multiple runs of measurement tests. The sensor signal displays excellent linear dependence between temperature and the corresponding frequency shift. The 2-point and 3-point MCCC-FPI sensors also exhibit fast response to environmental temperature changes. A three-point MCCC-FPI sensor has been further examined for temperature measurement up to 1000°C for multiple heating-cooling cycles and the results prove that the sensor is suitable for distributed temperature measurement up to 1000°C. MCCC-FPI sensors with more than 4 FPIs point in a single line are made in two structures: the first uses alumina tube as insulation and air gaps as reflectors; and the second uses air chamber as insulation and complete circular alumina discs (2 mm-thick) as reflectors. MCCC-FPIs in neither of the two structures are able to exceed four FPIs in a cable because the reflections from the FPIs are too strong for the microwave to transmit through >4 FPIs over a long distance. Specially shaped alumina discs made by removing parts of the circular discs are found to decrease the microwave reflectance because of reduced reflection areas. However, the smallest reflectance (in terms of percentage of the incident signal) obtained in this work is as high as 7.5%, which is still too large to construct more than 10 FPIs in a single MCCC. Nevertheless, the feasibility of the proposed multipoint MCCC-FPI has been demonstrated using air insulation and 2 mm-thick low-ε r Teflon discs as reflectors on a 2 m-long cable containing 10 FPIs (with reflectance <5% on each FPI). These results indicate that the contrast of dielectric constant between the insulation and reflector has a more significant impact on the reflectance. Thus, future research efforts should also be directed to developing ceramic materials (dense or porous) with low dielectric constant values which, when used as insulation or reflector, can realize large numbers of FPIs in a single cable over a long distance. To assist the development of high temperature dielectric materials, a novel MCCC-FPI sensor platform is developed and successfully demonstrated for measuring high frequency dielectric constants for fluids, packed dielectric solids, and ceramic tube materials and determining ε r dependencies on temperature and chemical composition, etc..
Ultra-High Temperature Distributed Wireless Sensors
Research was conducted towards the development of a passive wireless sensor for measurement of temperature in coal gasifiers and coal-fired boiler plants. Approaches investigated included metamaterial sensors based on guided mode resonance filters, and temperature-sensitive antennas that modulate the frequency of incident radio waves as they are re-radiated by the antenna. In the guided mode resonant filter metamaterial approach, temperature is encoded as changes in the sharpness of the filter response, which changes with temperature because the dielectric loss of the guided mode resonance filter is temperature-dependent. In the mechanically modulated antenna approach, the resonant frequency of a vibrating cantilever beam attached to the antenna changes with temperature. The vibration of the beam perturbs the electrical impedance of the antenna, so that incident radio waves are phase modulated at a frequency equal to the resonant frequency of the vibrating beam. Since the beam resonant frequency depends on temperature, a Doppler radar can be used to remotely measure the temperature of the antenna. Laboratory testing of the guided mode resonance filter failed to produce the spectral response predicted by simulations. It was concluded that the spectral response was dominated by spectral reflections of radio waves incident on the filter. Laboratory testing of the mechanically modulated antenna demonstrated that the device frequency shifted incident radio waves, and that the frequency of the re-radiated waves varied linearly with temperature. Radio wave propagation tests in the convection pass of a small research boiler plant identified a spectral window between 10 and 13 GHz for low loss propagation of radio waves in the interior of the boiler.
Laboratory evaluation of distributed coaxial cable temperature sensors for application in CO 2 sequestration well characterization: Original Research Article: Laboratory evaluation of distributed coaxial cable temperature
Downhole monitoring plays a crucial part in a geological carbon dioxide (CO 2 ) sequestration project, especially in providing early warnings of failure. However, most downhole monitoring technologies are often low in spatial resolution and time-consuming, or expensive and have system longevity issues. To address this issue, a robust and cost-effective distributed coaxial cable Fabry-Perot interferometer-based temperature sensor is proposed for real-time downhole monitoring. The coaxial cable sensor (CCS) was made in house and tested using a high pressure high temperature (HPHT) testing apparatus to study the sensor accuracy, sensitivity, stability, and crosstalk effect in simulated downhole conditions. The laboratory test results indicate that the sensor can work under simulated downhole conditions of pressures up to 1000 psia and temperatures up to 110°C. At 1 ATM, the sensor has an accuracy of about 1%. At 1000 psia, the hysteresis phenomenon is observed, but it is reduced and tends to stabilize after repeated heating and cooling treatments. The pressure crosstalk effect was observed on the flexible cable sensor and minimized on the rigid cable sensor. The temperature and pressure range of the distributed CCS allows long-term in situ monitoring for a well depth up to 2500 feet, which would prove of great value in detecting temperature change associated with wellbore leakage that may lead to groundwater contamination.