How to use fiber optic temperature measurement? What does fiber optic temperature measurement include

Światłowodowy czujnik temperatury, Inteligentny system monitorowania, Rozproszony producent światłowodów w Chinach

1、 The principle of światłowodowy pomiar temperatury

Fiber optic temperature measurement is based on the various optical properties of optical fibers that vary with temperature.

Principle of optical amplitude variation: In component type fiber optic temperature sensors, there is a situation where the optical amplitude varies with temperature. When the temperature changes, the core diameter and refractive index of the optical fiber will change, causing the light propagating in the fiber to scatter outwards due to uneven paths, ultimately resulting in changes in the amplitude of the light. Na przykład, in some high-precision laboratory measurement scenarios, this subtle change in light amplitude can be captured by special detection equipment, thereby obtaining the temperature change situation.
Principle of polarization plane rotation: The polarization plane of a single-mode fiber rotates with temperature, and the amplitude change can be obtained through a polarizer. Sensors based on this principle are of great significance in specific optical research or measurement scenarios sensitive to polarization rotation. Na przykład, when studying the relationship between certain optical materials and temperature, this sensor can be used to accurately obtain the effect of temperature on the rotation of the polarization surface.
Principle of optical phase change: When the length, refractive index, and core diameter of a single-mode fiber change with temperature, the light propagating in the fiber will undergo a phase change. This phase change can be obtained by an interferometer to measure the amplitude change. Na przykład, in a Mach Zehnder interferometer, light from a signal fiber is mixed with a stable reference beam. Due to the influence of temperature on the signal fiber, the phase of the propagating optical signal changes, causing interference between the two light columns. Więc, the change in phase can be detected to reflect the temperature change. In some environments that require extremely high temperature measurement accuracy, such as temperature monitoring in some precision instruments in aerospace, this measurement principle based on optical phase change can play an important role.
Based on the principle of spectral variation: the absorption spectrum of some substances changes with temperature, and real-time temperature can be understood by analyzing the spectrum transmitted by optical fibers. This principle is widely used in fiber optic temperature sensors, na przykład, in fiber optic fluorescence temperature sensors, the emitted fluorescence parameters have a one-to-one correspondence with temperature, and the required temperature can be obtained by detecting its fluorescence intensity or fluorescence lifetime. Some new types of fiber optic temperature sensors also utilize the thermal sensitivity and Bragg grating effect of optical fibers. Based on the principle that the reflected wavelength of Bragg fiber Bragg grating will shift with temperature, fiber optic grating temperature sensors are made. The sensing signal is wavelength modulated, and the measurement signal is not affected by factors such as light source fluctuations, fiber bending losses, connection losses, and detector aging.
Based on the principle of radiation energy conduction: For radiation (infrared) światłowodowe czujniki temperatury, it mainly utilizes the coupling and transmission characteristics of optical fibers to conduct the surface radiation energy of the measured object (which is related to the surface temperature of the measured object) to the photodetector and convert it into electrical output. This type of sensor is very practical in some non-contact temperature measurement scenarios, such as measuring the temperature outside a high-temperature furnace, and can obtain surface temperature information without direct contact with high-temperature objects.
Based on the principle of semiconductor absorption characteristics: In a semiconductor absorption type fiber optic temperature sensor, a cut optical fiber is installed in a thin steel pipe, and a semiconductor temperature sensing thin film (such as GaAs or InP) is sandwiched between the two ends of the fiber. The transmitted light intensity of this semiconductor temperature sensing thin film varies with the measured temperature. When a constant light intensity is input at one end of the optical fiber, the transmission ability of the semiconductor temperature sensing thin film changes with temperature, and the light intensity received by the receiving element at the other end of the optical fiber also changes with the measured temperature. Więc, by measuring the voltage output of the receiving element, the temperature at the sensor position can be remotely measured. In some scenarios where temperature monitoring is required for small devices or specific areas, this sensor can leverage its advantages of being compact and accurate in measurement.

2、 Technical methods for fiber optic temperature measurement

Point temperature measurement
Principle and operation: Deploy a single temperature probe in certain key areas of the system for measurement. This method is suitable for precise temperature measurement of specific points, such as temperature monitoring of a key chip in electronic devices, or temperature measurement of a specific point in a cell culture environment in biomedical research. It can provide very accurate local temperature information by placing the fiber optic probe at the target location and utilizing the optical properties of the fiber optic to obtain temperature data at that point.
Application scenario characteristics: In some devices or experimental scenarios that are highly sensitive to local temperature changes, point temperature measurement is essential. Na przykład, in ultra precision optical instruments, temperature changes in a small component may have a significant impact on the overall performance of the instrument. Point temperature measurement can accurately monitor the temperature of this component, providing a guarantee for the stable operation of the instrument. Ponadto, this measurement method is relatively simple and cost-effective, making it very practical for situations where only a few specific temperature points need to be monitored.
Quasi distributed measurement
Principle and operation: Connecting single point temperature measurements in series along the direction of fiber propagation can form a quasi distributed measurement that covers multi-point temperature detection. In the production of power systems, it is necessary to measure the temperature gradient field distribution in the airspace, and this technology can be effective. It can achieve temperature measurement at multiple points by connecting multiple measurement points in series on a single optical fiber, utilizing the transmission and temperature sensitivity characteristics of the fiber. Each measurement point can independently reflect temperature changes and transmit this temperature information to monitoring equipment for centralized processing through optical fibers.
Application scenario characteristics: In large power facilities such as substations, high-voltage transmission lines, itd., temperature monitoring of multiple key parts is required. Quasi distributed measurement can achieve temperature monitoring of multiple points on a single optical fiber, reducing the complexity and cost of wiring. W tym samym czasie, in some large industrial equipment or building structures, such as large boilers, bridges, itd., quasi distributed measurement technology can also be used to monitor the temperature at different locations, in order to timely detect potential temperature anomalies and prevent accidents.
Fully distributed measurement
Principle and operation: Fiber optics can serve as both a channel for optical signal transmission and a temperature sensitive material for conducting temperature changes. The distributed fiber optic temperature measurement system can be achieved by deploying a monitoring device and a sensing fiber. The monitoring cost per unit fiber length decreases with the increase of sensing distance, which is currently a highly promising engineering temperature measurement solution. It is based on the principle of optical time domain reflectometry (OTDR) of optical fibers and the Raman scattering effect of optical fibers. By analyzing the backward Raman scattering light in the optical fiber, it obtains temperature distribution information along the fiber. Laser pulses interact with fiber molecules, resulting in various scattering phenomena such as Rayleigh scattering, Rozpraszanie Brillouina, i rozpraszanie Ramana. The intensity of Raman scattering light is temperature dependent, and the temperature distribution along the fiber can be obtained by measuring the intensity changes of Raman scattering light.
Application scenario characteristics: In some scenarios that require temperature monitoring of a large area, such as long-distance oil pipelines, large storage facilities, itd., fully distributed measurement can use one optical fiber to achieve temperature monitoring of the entire area. It can provide accurate and continuous temperature data in real time, detect small temperature changes, and achieve real-time and fast multi-point measurement of spatial temperature distribution over a large range and long distance. This is of great significance for ensuring the safe operation of pipelines, preventing fires, and greatly reducing monitoring costs and complexity.
Fiber optic temperature sensing technology based on fluorescent radiation
Principle and Operation: The working mechanism of fluorescence temperature measurement is based on the fundamental physical phenomenon of photoluminescence. The so-called photoluminescence is a phenomenon of light emission, which refers to the emission of light when a material is excited by ultraviolet, visible, or infrared light. In fiber optic temperature sensors, the fluorescence characteristics of certain substances are utilized, and the intensity or lifetime of fluorescence changes when the temperature changes. Measure temperature by detecting changes in these fluorescence parameters. Na przykład, Mississippi State University in the United States uses a commercial epoxy adhesive as a temperature indicator (PAHs). PAHs emit fluorescence when excited by ultraviolet light, and the intensity of fluorescence decreases as the temperature around the epoxy adhesive increases. By detecting changes in fluorescence intensity, temperatures within the range of 20 ℃ to 100 ℃ can be measured.
Application scenario characteristics: This technology is more suitable in some scenarios where high temperature measurement accuracy is required and the environment is relatively stable. Na przykład, temperature monitoring in cell culture environments in the biomedical field, or temperature measurement in the study of heat dissipation performance of some small electronic devices. Due to the sensitivity of fluorescence characteristics to temperature changes and the ability to adapt to different temperature measurement ranges by selecting appropriate fluorescent materials, accurate temperature measurement results can be provided in these scenarios. Meanwhile, compared to other technologies, fluorescence radiation fiber optic temperature sensing technology may have a smaller device size, making it easier to use in environments with limited space.

3、 Application scenarios of fiber optic temperature measurement

Industrial sector
Power system: In power stations, fiber optic temperature sensors can be used to monitor the temperature of power generation equipment such as generators, Transformatory, itd. Na przykład, in transformers, fiber optic temperature sensors can monitor the oil temperature inside the transformer and the temperature of key components in real time, which helps to detect potential overheating problems in a timely manner and prevent serious accidents such as equipment damage or even fires caused by overheating. Ponadto, fiber optic sensors have the characteristic of resisting electromagnetic interference and can work stably in strong electromagnetic environments such as power systems. In high-voltage transmission lines, fiber optic temperature sensors can monitor the temperature of the line in real time. When the line experiences abnormal temperature rise due to overload or other reasons, they can provide timely warnings to ensure the safe operation of the transmission line.
Petrochemical industry: Fiber optic temperature sensors play an important role in the extraction, transport, and storage of petroleum. In oil wells, it can be used to monitor downhole temperature, understand the distribution of reservoir temperature, and provide data support for oil extraction. In terms of oil pipelines, fiber optic temperature sensors can be installed along the pipeline to monitor the temperature in real time. Once abnormal temperature is detected due to leaks or external environmental factors (such as the impact of permafrost melting on the pipeline), measures can be taken in a timely manner to prevent accidents such as oil spills. Monitoring the oil temperature inside the oil tank during storage helps ensure the quality and safe storage of the oil.
Manufacturing industry: In the manufacturing process of large machinery, such as automobile engines, aviation engines, itd., fiber optic temperature sensors can be used to monitor the temperature during the production process. Na przykład, monitoring the mold temperature during the engine casting process can optimize the casting process and improve product quality. Monitoring tool temperature during mechanical processing can adjust cutting parameters in a timely manner and extend tool life. W dodatku, temperature monitoring of key components can help ensure assembly accuracy in some high-precision mechanical assembly processes.
Medical field
Internal temperature monitoring of the human body: Fiber optic temperature sensors can be made into tiny probes for measuring the internal temperature of the human body. Na przykład, in some minimally invasive surgeries, fiber optic temperature sensors can be inserted into the human body through a catheter to monitor the temperature around the surgical site in real time, avoiding tissue damage caused by thermal damage during the surgery. During the process of tumor hyperthermia, fiber optic temperature sensors can accurately measure the temperature inside the tumor tissue, ensuring that the temperature of the hyperthermia is within the effective treatment range while avoiding overheating damage to surrounding normal tissues.
Medical equipment temperature monitoring: In some medical devices, such as magnetic resonance imaging (MRI) equipment, X-ray machines, itd., fiber optic temperature sensors can be used to monitor the temperature of key components inside the equipment. Due to the large amount of heat generated by these devices during operation, if the temperature of the components is too high, it may affect the performance of the equipment or even cause equipment failure. Through real-time monitoring by fiber optic temperature sensors, timely heat dissipation measures can be taken to ensure the normal operation of the equipment.
Environmental protection field
Atmospheric temperature monitoring: In meteorological research, fiber optic temperature sensors can be used for measuring atmospheric temperature. Compared with traditional meteorological temperature measurement equipment, fiber optic temperature sensors have the characteristics of anti electromagnetic interference and high accuracy. Fiber optic sensors can be installed on meteorological towers or balloons to measure atmospheric temperature at different heights, providing more accurate data for meteorological research, weather forecasting, i inne aplikacje.
Water temperature monitoring: In water environment monitoring, fiber optic temperature sensors can be used to measure the temperature of water bodies such as rivers, lakes, and oceans. Through long-term monitoring of water temperature, changes in the thermal environment of water bodies can be understood, which is of great significance for studying the impact of water ecosystems and climate change on water bodies. Na przykład, in some large lakes, by arranging fiber optic temperature sensors at different depths and locations, a water temperature distribution map of the entire lake can be drawn to analyze the impact of water temperature stratification on the lake ecosystem.
Soil temperature monitoring: In agricultural and ecological research, fiber optic temperature sensors can be used to monitor soil temperature. Soil temperature has a significant impact on the growth and development of plants. By monitoring soil temperature, guidance can be provided for agricultural production, such as determining the optimal sowing time, irrigation time, itd. In ecological research, changes in soil temperature can also affect the activity of soil microorganisms and the conversion of nutrients in the soil. Fiber optic temperature sensors can provide accurate temperature data for these studies.
Other special fields
In the aerospace field, fiber optic temperature sensors can be used to monitor the temperature of high-temperature components inside aircraft engines during testing and operation, ensuring the safe operation of the engine under extreme conditions such as high temperature and high pressure. In spacecraft, fiber optic temperature sensors can be used to monitor temperature changes outside the spacecraft, which is crucial for protecting internal equipment and instruments from extreme temperature fluctuations. Meanwhile, in the development process of aerospace materials, fiber optic temperature sensors can also be used to test the performance of materials under different temperature conditions.
Military field: In military equipment such as tanks, missiles, itd., fiber optic temperature sensors can be used to monitor the temperature of key components inside the equipment. During the launch process of missiles, fiber optic temperature sensors can monitor the temperature of missile engines and other components in real time, ensuring the normal launch and flight of missiles. In the construction and maintenance of military facilities, fiber optic temperature sensors can be used to monitor environmental temperature, ensuring the safety and stability of military facilities.

4、 Factors affecting the accuracy of fiber optic temperature measurement

Factors related to the inherent characteristics of optical fibers
Fiber optic materials: Different fiber optic materials have different coefficients of thermal expansion and optical properties, which can affect the accuracy of temperature measurement. Na przykład, certain special fiber optic materials may experience significant refractive index changes when subjected to temperature fluctuations, while others remain relatively stable. If inappropriate fiber optic materials are selected in high-precision temperature measurement scenarios, it may lead to significant deviations in measurement results.
Długość włókna: Temperature changes can cause changes in fiber length. According to the principle of thermal expansion and contraction, when the temperature changes by 1 °C, the change in length of single-mode fiber per kilometer may not differ significantly. Jednak, in long-distance fiber temperature measurement, the accumulation of these small length changes may affect measurement accuracy. Na przykład, in long-distance distributed fiber optic temperature measurement systems, if the changes in fiber length due to temperature variations cannot be accurately compensated for, it may lead to misjudgment of temperature.
The refractive index variation of optical fibers: The refractive index of optical fibers varies with temperature, which affects the propagation characteristics of light in optical fibers, such as the phase and propagation speed of light. When the refractive index of optical fibers changes due to temperature fluctuations, fiber optic sensors that measure temperature based on phase changes or light propagation time will be affected, thereby reducing measurement accuracy.
External environmental factors
The complexity of environmental temperature changes: The environmental temperature itself may be uneven, with temperature gradients or rapid temperature fluctuations. In such a complex temperature environment, fiber optic sensors may not accurately reflect the true temperature situation. Na przykład, in outdoor environments, there is a large temperature difference between day and night, and direct sunlight during the day may cause the local temperature of the fiber optic cable to rise, while at night it will rapidly decrease. This frequent temperature change will pose a challenge to measurement. Ponadto, the environmental temperature may also be affected by factors such as airflow and humidity, further increasing the complexity of temperature measurement.
External interference sources: In some special application scenarios, the presence of external interference sources may affect the accuracy of fiber optic temperature measurement. Na przykład, in industrial environments, there are factors such as strong electromagnetic fields, vibration, and chemical corrosion. Strong electromagnetic fields may interfere with the transmission of optical signals in fiber optic sensors, leading to measurement errors; Vibration may cause slight bending or displacement of optical fibers, affecting the propagation path of light and thus affecting measurement accuracy; Chemical corrosion may damage the surface of optical fibers or alter their optical properties, reducing the performance of sensors.
Factors related to sensor devices
Light source stability: For fiber optic temperature sensors, the stability of the light source is crucial. If the intensity or wavelength of the light source fluctuates, it will affect the accuracy of sensors that measure temperature based on changes in light intensity or wavelength. Na przykład, in fiber Bragg grating temperature sensors, the fluctuation of the light source may lead to inaccurate measurement signals because the sensing signal is wavelength modulated, and the instability of the light source can cause wavelength measurement deviations.
Performance of photodetector: The sensitivity, wavelength resolution, and other performance indicators of the photodetector will affect the measurement accuracy. If the sensitivity of the photodetector is insufficient, it may not be able to accurately detect weak changes in the light signal, thereby affecting temperature measurement. Na przykład, in fiber optic temperature sensors based on fluorescence radiation, it is necessary to detect small changes in fluorescence intensity or lifetime. If the sensitivity of the photodetector is not sufficient, these changes cannot be accurately obtained, leading to temperature measurement errors. Meanwhile, the wavelength resolution of the photodetector is not high, which can also reduce the measurement accuracy when measuring fiber optic temperature sensors based on wavelength changes.
Packaging and installation of sensors: The packaging material and structure of sensors can affect the conduction of heat and the response speed of sensors to temperature. If the thermal conductivity of the packaging material is poor, it will cause the sensor to lag in response to temperature changes, thereby affecting measurement accuracy. During the installation process, if there is poor contact between the sensor and the object being measured, or if the installation position is not reasonable, the measurement results may not accurately reflect the true temperature of the object being measured. Na przykład, when measuring the temperature of small electronic device chips, if the fiber optic temperature sensor is not installed in close contact with the chip, it may measure the temperature of the surrounding environment instead of the actual temperature of the chip.

5、 Equipment types for fiber optic temperature measurement

Component type fiber optic temperature sensor
Working principle and characteristics: Component based fiber optic temperature sensors use the characteristics of the fiber itself to sense temperature changes and measure them. Na przykład, using a sensor that changes the amplitude of light with temperature, the core diameter and refractive index of the optical fiber change with temperature, causing the light propagating in the fiber to scatter outward due to uneven paths, resulting in changes in light amplitude; Using a sensor that rotates the polarization surface of a single-mode fiber, the polarization surface of the fiber rotates with temperature, and the amplitude change is obtained through a polarizer; By using a sensor that detects changes in optical phase, the length, refractive index, and core diameter of a single-mode fiber vary with temperature, causing a phase change in the light propagating in the fiber. This phase change is then measured by an interferometer to obtain amplitude changes. The advantage of component type fiber optic temperature sensors is that they directly utilize the characteristics of the fiber itself and have high sensitivity. Jednak, its disadvantage is that it requires high quality and performance of the optical fiber, and requires more precise instruments and technology to ensure measurement accuracy during manufacturing and use.
Application scenario: It is more suitable for temperature monitoring scenarios in laboratory research or high-end precision instrument equipment that require extremely high temperature measurement accuracy and relatively stable measurement environments. Na przykład, temperature monitoring inside high-precision optical instruments, or precise measurement of small temperature changes in physical and chemical experiments.