Como você mede a temperatura do cabo?-INNO

The distributed fiber optic temperature measurement system measures the intensity ratio of anti Stokes light and Stokes light through the Raman scattering effect of laser pulses in the fiber optic cable, thereby determining the temperature at each point of the cable.

1、 O princípio de distributed fiber optic cable temperature measurement

Distributed fiber optic cable temperature measurement is based on spontaneous Raman scattering effect and optical time domain reflectometry (OTDR) tecnologia.
Efeito de dispersão Raman: When a high-power narrow pulse laser LD is incident on a sensing fiber, the interaction between the laser and fiber molecules produces extremely weak backscattered light, which includes three wavelengths: Rayleigh, anti Stokes, and Stokes light. Entre eles, anti Stokes light is temperature sensitive and can be used as signal light; A luz de Stokes é insensível à temperatura e pode ser usada como luz de referência. A vibração térmica das moléculas de fibra gera espalhamento Raman, resultando na formação de luz Stokes e luz anti Stokes. A intensidade do sinal de luz anti-Stokes depende da temperatura, e a temperatura de qualquer ponto no guia de ondas óptico pode ser determinada pela razão entre o sinal de luz anti-Stokes e a intensidade do sinal de luz de Stokes. Por exemplo, quando a temperatura de um cabo aumenta em um determinado ponto, a intensidade da luz anti-Stokes nesse ponto mudará de acordo. Comparando e calculando com a intensidade da luz de Stokes, o valor da temperatura pode ser obtido. This method of measuring temperature using Raman scattering effect has the characteristic of high accuracy and can meet the needs of cable temperature monitoring.
OTDR technology: The determination of position is based on OTDR technology. When light is transmitted in optical fibers, scattering occurs due to the microscopic non-uniformity of refractive index in the fibers. By using high-speed data acquisition to measure the echo time of scattered signals, the position of the fiber corresponding to the scattered signal can be determined. Because the transmission speed of light in optical fibers is fixed, by measuring the time from emission to reception of light pulses, the location where scattering occurs can be accurately calculated, thereby achieving the positioning of temperature measurement points along the optical fiber. Por exemplo, if a temperature anomaly occurs at a certain location on a 10 kilometer long fiber optic cable, OTDR technology can accurately locate the specific coordinates of that location on the fiber optic cable. This technology enables fibra óptica distribuída temperature measurement systems to not only measure temperature, mas também localizar com precisão a localização das anomalias de temperatura, which is crucial for cable temperature monitoring because it can detect local hotspots on the cable in a timely manner, making it easier to take corresponding measures.

Monitoramento distribuído de fibra óptica

2、 Method for Distributed Fiber Optic Measurement of Cable Temperature

Fiber optic laying: Primeiramente, the fiber optic cable should be laid around or inside the cable. If the cable has a multi-layer structure, such as a conductor layer, insulation layer, buffer layer, waterproof layer, e bainha externa dispostas em sequência de dentro para fora, o impacto da posição de colocação da fibra na precisão da medição de temperatura precisa ser considerado. De um modo geral, quanto mais próxima a fibra óptica estiver de uma possível fonte de calor (such as a conductor layer), mais sensível é às mudanças de temperatura. No entanto, também é necessário evitar danos à fibra óptica por fatores físicos durante a operação do cabo (como dobrar cabos, alongamento, etc.). Em algumas aplicações práticas, como em túneis de cabos, as fibras ópticas podem ser colocadas ao longo de bandejas de cabos ou paralelamente aos cabos em valas de cabos para garantir que as fibras ópticas possam entrar em contato total com o campo de temperatura ao redor dos cabos.
Aquisição e processamento de sinal: Pulsos de laser de pulso estreito de alta potência LD incidem na fibra de detecção, gerando luz retroespalhada. The anti Stokes and Stokes light pass through the splitter module WF, isolating the Rayleigh scattered light, and are received by the same detector (DPA). Obtain temperature information by measuring and calculating the ratio of these two light intensities. This process requires high-precision detection equipment and signal processing algorithms to accurately distinguish and process weak scattered light signals. Em termos de coleta de dados, it is necessary to ensure that the frequency and accuracy of data collection meet the requirements of cable temperature monitoring. Por exemplo, in cable environments with rapid temperature changes, a higher collection frequency is required to capture the dynamic changes in temperature in a timely manner.
Temperature calculation and positioning: Based on the ratio of the received anti Stokes and Stokes light intensities, use a predetermined mathematical model to calculate the temperature value. Ao mesmo tempo, the optical time domain reflectometry (OTDR) technology is used to determine the position of the temperature measurement point on the optical fiber, thereby achieving a one-to-one correspondence between temperature and position. When calculating temperature, it is necessary to consider the optical properties of optical fibers, parameters of laser pulses, and environmental factors that affect the measurement results. Por exemplo, losses in optical fibers, power fluctuations in laser pulses, and other factors can all affect the accuracy of the light intensity ratio, thereby affecting the accuracy of temperature calculations. In terms of positioning, é necessário garantir a precisão do posicionamento para que a posição correspondente possa ser encontrada com precisão quando o cabo apresentar anormalidades de temperatura.

3、 Instrumento e equipamento para medição distribuída de temperatura de cabos em fibra óptica

Host de medição de temperatura de fibra óptica distribuída:
Este é o equipamento principal do sistema distribuído de medição de temperatura de fibra óptica. Ele pode gerar pulsos de laser de pulso estreito de alta potência e acoplá-los em fibras de detecção. Por exemplo, o host de medição DTS8000 pode usar pulsos de laser semicondutores de pulso estreito de alta velocidade acoplados a fibras de detecção. Filtrando, detecção, e aquisição de dados em alta velocidade e análise de sinais de retroespalhamento fracos na fibra, pode obter sinais anti-Stokes sensíveis à temperatura e sinais de Stokes insensíveis à temperatura, thereby obtaining accurate temperature information distributed along the fiber in real time.
It has diversified functions such as signal processing, análise de sinal, aviso de alta temperatura, e transmissão de dados. It is possible to process and analyze the collected optical signals, calculate the temperature value based on pre-set algorithms, and determine whether there are temperature anomalies. Uma vez detectada uma situação anormal, the relay output can quickly drive the external sound and light alarm equipment and other linkage devices to ensure timely and effective handling of the abnormal situation.
Different models of temperature measurement hosts have differences in measurement distance, precisão de medição, measurement time, number of channels, e outros aspectos. Por exemplo, some hosts can measure distances of up to 30KM or even longer, com uma precisão de medição de ± 1 ℃, a measurement time of about 3-15s, e 1-8 canais de medição.
Thermal fiber optic cable:
It is both a carrier for signal transmission and a temperature sensing element. Its characteristics directly affect the accuracy and reliability of temperature measurement. Por exemplo, temperature sensing optical cables with mining armor, retardador de chama, and central bundle tube have good compressive strength (short-term 3000, longo prazo 1500) and tensile strength, suitable for cable temperature monitoring in special environments such as coal mines.
Different types of optical fibers (such as single-mode and multi-mode) can be used for different measurement scenarios. Single mode fiber is suitable for long-distance and high-precision temperature measurement; Multimode fiber has advantages in some short distance and cost sensitive application scenarios.
The length of the temperature sensing optical cable is determined according to the measurement requirements, and can be as long as several kilometers or even tens of kilometers, enabling continuous temperature monitoring of longer cable lines.
Other supporting equipment:
Spectral module WF: used to isolate Rayleigh scattered light, so that temperature sensitive anti Stokes signal light and temperature insensitive Stokes reference light can be received by the same detector (DPA), providing accurate light intensity signals for subsequent temperature calculations.
Detector (DPA): responsible for receiving anti Stokes signal light and Stokes reference light processed by the splitting module, converting the optical signal into an electrical signal for subsequent signal processing and temperature calculation.

4、 Practical case of distributed fiber optic cable temperature measurement

Application in Fire Detection of Cable Tunnels:
There are a large number of cable tunnels in places such as power plants and steel plants, which are prone to fires due to cable heating and faults. Distributed fiber optic temperature measurement technology is based on the principles of optical time domain reflectometry (OTDR) and backward Raman scattering of optical fibers, which can accurately, oportuno, and continuously monitor the temperature inside cable tunnels. Por exemplo, by laying the detection fiber in a cable tunnel, the fiber optic host emits a laser beam into the detection fiber optic cable and collects real-time Raman scattering light with on-site real-time temperature information scattered back along the fiber optic cable. These light signals are analyzed and processed to obtain temperature distribution information on the entire fiber optic cable. When the temperature exceeds the preset alarm value, the fiber optic host emits a fire alarm sound and light indication, and can output alarm information to the fire alarm controller.
The composition of the distributed fiber optic temperature measurement system includes sensing optical cables laid on site, whose function is to obtain the temperature of the on-site cable tray and the ambient temperature; Each distributed fiber optic temperature measurement host is installed in the monitoring room or cable tray or tunnel according to the principle of proximity (if directly installed on site, outdoor equipment with a protection level of IP66 should be selected), responsible for collecting and calculating the temperature measured by the sensing fiber optic cable in real time; O servidor de monitoramento coleta dados de temperatura de vários hosts de medição de temperatura, lojas, exibições, gerencia, análises, exportações, e imprime os dados executando o software de monitoramento de temperatura. Ele também pode usar o protocolo Modbus para conectar-se ao controlador de alarme de incêndio e enviar sinais de alarme diretamente para o controlador de alarme de incêndio., alcançar a ligação.
Aplicação na construção de poder de comunicação:
O distribuído sistema de monitoramento de temperatura de fibra óptica é usado para monitoramento de temperatura na sala de informática do prédio de energia de comunicação, incluindo monitoramento de temperatura de gabinetes, cabos de ponte, e cabos de túneis subterrâneos. O sistema inclui um cliente local, host de medição de temperatura de fibra óptica, cabo óptico com detecção de temperatura, e software de medição de temperatura. Ao detectar a temperatura através de cabos ópticos com detecção de temperatura, o host de medição de temperatura de fibra óptica coleta e processa dados, transmite informações de temperatura para clientes locais e software de medição de temperatura, realizes real-time temperature monitoring, análise de tendências, and remote warning and alarm, ensuring safe and stable communication operation. Por exemplo, when the temperature of the cable tray in the computer room rises abnormally due to high load, o distributed fiber optic temperature monitoring system can detect the temperature change in a timely manner, analyze it through software to determine whether it has reached the alarm threshold, and if it has, issue an alarm signal to notify relevant personnel for inspection and handling, thereby avoiding communication failures or safety accidents such as fires caused by high cable temperature.

5、 Precautions for distributed fiber optic cable temperature measurement

Regarding fiber optic laying and installation:
The laying path of optical fibers should be planned reasonably to avoid being affected by external mechanical stress. If the optical fiber is excessively bent, stretched, or compressed during the laying process, it may increase fiber loss, affect the transmission of optical signals, and thus reduce the accuracy of temperature measurement. Por exemplo, when laying optical fibers in cable trenches, attention should be paid to the compression of the fibers by other equipment or debris in the trench to ensure that there is sufficient space for the fibers.
The coupling method between optical fibers and cables is also important. If the coupling is improper, it may not be possible to accurately sense the temperature changes of the cable. When installing optical fibers on cables, appropriate coupling methods should be selected based on the type, estrutura, and working environment of the cable, such as tying, pasting, or fixing with specialized fixtures, to ensure that the optical fibers are in close contact with the cable and can effectively conduct heat.
For long-distance fiber optic installation, the issue of fiber optic splicing should be considered. Fiber optic splice points may introduce losses and reflections, affecting temperature measurement. Portanto, high-quality splicing equipment and processes should be used during fiber optic splicing to ensure minimal loss at the splicing point.
In terms of calibration and maintenance of measurement systems:
Regular calibration of distributed fiber optic temperature measurement systems is key to ensuring measurement accuracy. Due to the potential impact of environmental temperature, umidade, fiber aging, and other factors on the measurement accuracy of the system, it is necessary to regularly calibrate the system using a standard temperature source. Por exemplo, the measurement results of the system can be compared and adjusted in a constant temperature environment with a known temperature to ensure that the measurement error is within the allowable range.
Regular maintenance should be carried out on temperature measurement hosts, detectores, e outros equipamentos. Check the operating status of the equipment, clean the surface of the equipment, and prevent dust, water vapor, etc.. from entering the interior of the equipment and affecting its performance. For APD detectors, their sensitivity and response speed should be regularly checked to ensure accurate reception and conversion of optical signals.
Regular inspections should also be conducted on temperature sensing optical cables to check for any damage, breakage, or corrosion. If damage is found to the optical cable, it should be repaired or replaced in a timely manner to ensure the continuity and accuracy of temperature measurement.
In terms of the impact of environmental factors:
Changes in environmental temperature and humidity may affect the optical properties of optical fibers and the performance of equipment. Por exemplo, in high temperature and high humidity environments, the loss of optical fibers may increase, and electronic components inside the equipment may experience performance degradation or failure. Portanto, when using a distributed fiber optic temperature measurement system in this environment, corresponding protective measures should be taken, such as sealing, à prova de umidade, e tratamento de dissipação de calor do equipamento.
Se houver forte interferência eletromagnética no ambiente de medição, embora as próprias fibras ópticas tenham a característica de resistir à interferência eletromagnética, dispositivos eletrônicos no sistema (como hosts de medição de temperatura) pode ser afetado. Nesse caso, blindagem eletromagnética deve ser aplicada a dispositivos eletrônicos para garantir que o sistema possa funcionar corretamente. Ao mesmo tempo, também é necessário evitar colocar fibras ópticas perto de fontes fortes de radiação eletromagnética para evitar interferência com os sinais ópticos nas fibras.