How to use fiber optic to monitor temperature? Σύστημα μέτρησης θερμοκρασίας οπτικών ινών, εφαρμογή, complete guide, 2025

Αισθητήρας θερμοκρασίας οπτικών ινών, Έξυπνο σύστημα παρακολούθησης, Κατανεμημένος κατασκευαστής οπτικών ινών στην Κίνα

1. Principle of Fiber Optic Temperature Monitoring

Fiber optic temperature sensor is an advanced sensor that measures temperature changes by utilizing optical effects. It utilizes the unique properties of optical fibers, such as their thermal sensitivity and Bragg grating effect. The basic principle is to use the optical properties of optical fibers to reflect changes in environmental temperature by measuring the optical signal parameters (such as light intensity, phase, κλπ.) in the fiber. The following are several common fiber optic temperature monitoring methods based on different principles:

1.1: Based on the principle of light amplitude variation:

 

In component type fiber optic temperature sensors, the core diameter and refractive index of the fiber change with temperature, causing the light propagating in the fiber to scatter outward due to uneven paths, resulting in changes in light amplitude. Για παράδειγμα, in some special fiber structures, changes in temperature can cause changes in the material distribution or structural characteristics inside the fiber, resulting in changes in the scattering of light during propagation, and thus causing changes in the amplitude of light. By detecting these amplitude changes, temperature information can be obtained.
Based on the principle of interference: In the instrument, light from the signal fiber is mixed with a stable reference beam. Due to the influence of the measured parameters (such as temperature) on the signal fiber, the phase of the propagating optical signal changes, resulting in interference between the two light beams. In principle, a suitable phase detector can detect small changes, while a stripe counter can detect large changes. This utilizes the interference characteristics of light, converting the influence of temperature on the phase of optical signals in optical fibers into detectable interference phenomena, thereby achieving temperature monitoring.

1.2: Based on the principle of Raman scattering effect:

The basic principle of distributed fiber optic temperature sensing system (DTS) is based on the optical time domain reflectometry (OTDR) principle of fiber optic and the Raman scattering effect of fiber optic. Laser pulses interact with fiber molecules, resulting in various scattering phenomena such as Rayleigh scattering, Brillouin scattering, and Raman scattering. Select the Raman scattering that is most sensitive to temperature changes when selecting the system reference signal. The mechanism of fiber optic temperature measurement is based on the backward Raman scattering effect, which obtains temperature information by analyzing the Raman scattering light signal. Because the intensity of Raman scattering light has a specific relationship with temperature, temperature changes can cause changes in Raman scattering intensity. By measuring the changes in Raman scattering intensity, the temperature value can be determined.

1.3: Based on the principle of Bragg fiber Bragg grating:

In quasi distributed fiber optic temperature measurement technology, a representative solution is a temperature measurement system with multiple fiber Bragg gratings connected in series. Several Bragg fiber gratings with different center wavelengths are formed by exposure and etching along the longitudinal direction of the optical fiber through ultraviolet radiation. Each Bragg fiber grating is power total reflection for a specific wavelength of light. When the ambient temperature of the fiber Bragg grating changes, the wavelength of the reflected signal from the grating will also change. Inject a beam of broad-spectrum light containing multiple wavelengths into an optical fiber, and the beam passes through a series of fiber Bragg gratings. Each grating reflects a monochromatic light signal corresponding to its wavelength, and temperature changes are reflected by detecting changes in the reflected light wavelength.

1.4: Based on the principle of fluorescence radiation:

In fluorescence radiation fiber temperature sensing technology, a fluorescent substance is coated on the end of the fiber, and the temperature value of the measured point can be obtained by measuring the decay time of fluorescence energy and utilizing the temperature correlation of the intrinsic afterglow time of the fluorescent substance. The afterglow time of fluorescent substances changes with temperature, and this characteristic is used for temperature measurement. Its applicable temperature range is -50~200 ℃, with an accuracy of about ± 1 °C, and it is commonly used for temperature measurement inside electrical equipment.

1.5: Principle of Light Absorption/Transmission Characteristics Based on Gallium Arsenide Crystals:

Gallium Arsenide Fiber Temperature Measurement Technology embeds gallium arsenide crystal material into the far end of the fiber as a temperature probe, and injects incident light into the near end device of the fiber. When the sensor light source emits multi wavelength incident light and radiates onto the gallium arsenide crystal, the gallium arsenide crystal material will absorb different wavelengths of incident light at different temperatures, and the unabsorbed wavelengths of light will be reflected back to the device. By analyzing the spectrum of reflected light, the temperature parameters at the probe can be obtained. The advantage of this sensor is that it obtains the probe temperature through absolute spectral measurement rather than temperature change measurement, so it does not involve on-site calibration. The probe has good universality, and the sensing distance can exceed 500m. The light source life and long-term stability of online detection can exceed 30 years. Όμως, the cost of gallium arsenide fiber is relatively high.

2. Method of Fiber Optic Temperature Monitoring

According to different application scenarios, fiber optic temperature measurement technology can be divided into the following categories:

2.1: Point temperature measurement:

Fluorescence radiation fiber temperature sensing technology: a fluorescent substance is coated on the end of the fiber, and the temperature value of the measured point is obtained by measuring the decay time of fluorescence energy and utilizing the temperature correlation of the intrinsic afterglow time of the fluorescent substance. Suitable for temperature range of -50~200 ℃, with an accuracy of about ± 1 °C, currently mainly used for temperature measurement inside electrical equipment. It has the characteristics of small size, easy integration, reliable performance, αντιηλεκτρομαγνητικές παρεμβολές, good insulation performance, convenient installation, and flexible networking.

2.2 Gallium Arsenide Fiber Optic Temperature Measurement Technology:

Embedding gallium arsenide crystal material into the far end of the optical fiber as a temperature probe, injecting incident light into the near end device of the fiber. When the sensor light source emits multi wavelength incident light and radiates onto the gallium arsenide crystal, the gallium arsenide crystal material absorbs different wavelengths of incident light at different temperatures, and the unabsorbed wavelengths of light are reflected back to the device. The temperature parameters at the probe are obtained by analyzing the spectrum of the reflected light. Its advantages are that the probe temperature is obtained through absolute spectral measurement, without on-site calibration, the probe has good universality, the sensing distance can exceed 500m, the light source life and online detection long-term stability exceed 30 years, but the cost is relatively high.

2.3 Quasi distributed measurement:

Fiber Bragg Grating Series Temperature Measurement System: Through ultraviolet radiation along the longitudinal direction of the fiber, several Bragg fiber gratings with different center wavelengths are formed by exposure and etching. Each Bragg fiber grating is power total reflection for a specific wavelength of light. Multiple Bragg fiber gratings are sequentially connected in series in the direction of fiber propagation to form a spatially discrete quasi spatial distribution temperature measurement system. Injecting broadband light into an optical fiber, when the beam passes through a fiber Bragg grating, each grating reflects a monochromatic light signal corresponding to its wavelength. When the ambient temperature of the fiber Bragg grating changes, the wavelength of the grating reflected signal will change. Its probe has a small volume, the optical path can be appropriately bent, it is resistant to electromagnetic radiation, and easy to telemetry. Όμως, the mechanical strength of the fiber Bragg grating is low, and it is easily damaged under complex working conditions, which requires the reliability of the sensor. Επιπλέον, the sensitivity of wavelength demodulation is a problem, and the wavelength drift of reflected light caused by a temperature rise of tens of degrees does not exceed 1nm.

2.4 Fully distributed measurement:

Distributed Fiber Temperature Measurement System (DTS) Based on Raman Scattering Effect: Utilizing the Optical Time Domain Reflector (OTDR) principle of optical fibers and Raman scattering effect. Laser pulses interact with fiber molecules to generate various scattering phenomena such as Raman scattering, and temperature is measured based on the Raman scattering effect. This system can be implemented by deploying a monitoring device and a sensing fiber, and the monitoring cost per unit fiber length decreases with the increase of sensing distance. It is currently a highly promising engineering temperature measurement solution. It can achieve temperature measurement in single point, multi-point, and continuous areas, and can serve as a medium for temperature measurement and transmission simultaneously. It has anti electromagnetic interference ability, αντοχή στη διάβρωση, good insulation performance, flexible installation methods, can be linked with fire protection, alarm systems, κλπ. It can also remotely transmit data, view and control remotely, and has advantages such as data analysis and fault point troubleshooting.

3. Application case of fiber optic temperature monitoring

 

3.1 Application in Communication Power Building:

Problem solved: The communication room has dense equipment and high security requirements. Once a fire occurs, it will cause the entire communication network to be paralyzed, requiring real-time monitoring of the room temperature. And with the rapid development of 5G technology, communication rooms are rapidly being built and expanded, resulting in a sudden increase in the number and power of equipment in the rooms. Traditional electronic temperature measurement methods have disadvantages such as limited temperature measurement points, complex installation of transmission cables, and are not conducive to maintenance and management.
Specific implementation plan: Install a distributed fiber optic temperature monitoring system (such as FGT series) on the equipment and lines in the computer room to achieve real-time temperature monitoring, trend analysis, remote accurate detection of accidents, early warning, alarm and other functions. The core part of the system mainly consists of a local client, Οικοδεσπότης μέτρησης θερμοκρασίας οπτικών ινών, temperature sensing optical cable, and temperature measurement software. Για παράδειγμα, temperature sensing optical fibers enter each cabinet from below and measure the temperature inside the cabinet by circling around the front and back of the cabinet; The temperature measuring optical fiber is laid in an S-shape along the cable tray on the surface of the cable tray for temperature monitoring of the cable tray; The temperature measuring optical fiber is laid along the underground tunnel cable route on the surface of the cable for temperature monitoring of the tunnel cable; Upload to the local client and monitoring center client via TCP/IP protocol, and the client can display real-time temperature information of each cabinet through monitoring software. Based on the obtained real-time temperature, draw a temperature cloud map of the computer room; When an abnormal high temperature alarm occurs at a certain location in the computer room, the temperature measurement host transmits the alarm information to the alarm system through the RS485 serial protocol for corresponding fire extinguishing treatment.
Application value: In addition to regional alarms, early warning positioning can also locate and set the temperature of alarm points; Real time temperature display can accurately determine the development trend of fire accidents and provide data basis for firefighting; It has the advantages of safety and reliability (υψηλή ευαισθησία, no electromagnetic interference, passive real-time monitoring, good electrical insulation, αντιεκρηκτική προστασία, combined with fixed and differential temperature alarms, no false alarms), εύκολη εγκατάσταση (fiber optic anti tension, anti impact, small outer diameter, good flexibility, μικρός όγκος, light weight, can be wound and installed on the surface of the testing area in a straight or snake shape), efficient use (long-distance monitoring, detection and signal transmission can be completed by one optical cable, all set at the terminal, the entire system is simple and reliable, and the operation and maintenance workload is minimal), and ultra long service life (the built-in constant temperature circuit system and advanced microcomputer electro-optical switch greatly improve the service life of the equipment, with a service life of more than 15 years).

3.2 Applications in the field of transportation:

In road tunnels, fiber optic sensors can be used to monitor parameters such as temperature and humidity inside the tunnel, detect dangerous situations such as fires and floods in a timely manner, and trigger alarm systems to ensure the safety of vehicles and passengers. Fiber optic sensors also have important application value in the construction of intelligent transportation systems and vehicle safety monitoring, such as monitoring the temperature of key parts of vehicles to ensure the safety and reliability of vehicle operation.

3.3 Application in power plants:

Compared with the traditional temperature sensing cable, the optical fiber temperature monitoring system is progressiveness. In power plants, fiber optic temperature sensors can monitor the temperature of equipment in real time during operation, such as temperature monitoring of large equipment such as generators and transformers. They can detect abnormal situations such as overheating in a timely manner, thereby avoiding equipment failures and ensuring the normal operation of power plants.

4. Recommended Fiber Optic Temperature Monitoring Equipment

FJINNO’s IF-C fluorescence fiber optic temperature measurement system:
Fluorescence anti-interference ability and measurement method: It has the characteristic of resisting electromagnetic interference, and optical fiber as a signal transmission medium is not affected by electromagnetic interference, ensuring accurate temperature monitoring near high-voltage power equipment. Support multi-point measurement, multiple measurement interfaces can be set on a fluorescent fiber optic temperature transmitter to achieve multi-point temperature monitoring.

5. How to choose a suitable fiber optic temperature monitoring solution

 

5.1: Consider the requirements of the measurement scenario:

Temperature range requirements: Different fiber optic temperature monitoring technologies are applicable to different temperature ranges. Για παράδειγμα, the fluorescence radiation fiber optic temperature sensing technology is suitable for a temperature range of -50~200 ℃. If the ambient temperature to be measured is low or high, a customized fiber optic temperature monitoring scheme that can cover this temperature range is required.

5.2: Measurement points and areas:

If it is a single point temperature measurement, such as measuring temperature at a key part inside an electrical equipment, point based temperature measurement methods such as fluorescence radiation fiber temperature sensing technology or gallium arsenide fiber temperature measurement technology are more suitable; If temperature monitoring is required for continuous areas or multiple points, such as cabinets, σχάρες καλωδίων, and underground tunnel cables in communication power buildings, distributed fiber optic temperature monitoring systems (DTS) are more suitable for temperature monitoring in multiple areas.

5.3: Consider the performance characteristics of the sensor:

Accuracy and stability: In some scenarios that require high temperature measurement accuracy, such as real-time temperature monitoring during surgical procedures in the medical field, high-precision fiber optic temperature sensors need to be selected.

5.4: Sensor response speed:

In some scenarios where rapid temperature changes are required, such as fire alarm systems, sensors need to have a fast response speed to detect abnormal temperature increases in a timely manner and issue alarms. The response speed of different fiber optic temperature sensors varies and needs to be selected according to specific application scenarios.

5.5: Consider cost factors:

Equipment cost: The manufacturing process of high-performance fiber optic temperature sensors is complex and costly, which limits their large-scale application. Για παράδειγμα, gallium arsenide fiber optic sensors have many advantages, but their cost is relatively high. In the case of limited budget, it is necessary to comprehensively consider equipment costs and choose a cost-effective fluorescent fiber temperature monitoring solution.

5.6: Installation and maintenance costs:

The complexity of installing different fiber optic temperature monitoring solutions varies, and installation costs may also differ. Για παράδειγμα, in the distributed fiber optic temperature monitoring system in the communication power building, the laying method of fiber optic cables, installation and commissioning of equipment will all affect the installation cost. Ταυτόχρονα, maintenance costs also need to be considered, such as the service life of the equipment, whether it is prone to malfunctions, and the difficulty of repairing after a malfunction. Some devices with self diagnosis and remote maintenance functions may have higher equipment costs, but in terms of long-term maintenance costs, they may be more cost-effective.