optical temperature sensor

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Overview of Fluorescent Fiber Optic Temperature Sensor

Fluorescent fiber optic temperature sensor is a type of sensor that utilizes the characteristics of fluorescent materials for temperature measurement. It consists of multimode optical fibers and a fluorescent object (film) mounted on top. When a fluorescent substance is excited by light of a certain wavelength (excitation spectrum), it emits fluorescence energy upon excitation. After the excitation is cancelled, the persistence of fluorescence afterglow depends on factors such as the characteristics of the fluorescent substance and environmental temperature. This excited fluorescence usually decays exponentially, with the decay time constant being the fluorescence lifetime or fluorescence afterglow time (ns). At different ambient temperatures, the decay of fluorescence afterglow varies, so the ambient temperature can be determined by measuring the lifetime of fluorescence afterglow. Its core technology lies in fluorescent substances and corresponding simulation algorithms. The temperature measuring fluorescent material is calcined at a high temperature of 1200 degrees, which has long lifespan, stable and reliable working characteristics, suitable for large-scale industrial production, and can be widely applied in the industrial field. A typical fluorescent fiber optic temperature sensor includes a light source, optical fiber, fluorescent material, and spectrometer. The light source generates excitation light of a certain wavelength, which is transmitted to the fluorescent material through an optical fiber. The fluorescent material absorbs the excitation light and emits a specific wavelength of fluorescent light signal, which is then transmitted back to the spectrometer for detection through the optical fiber. When the temperature changes, the flash characteristics (fluorescence intensity or wavelength) of the fluorescent material change, and the temperature value can be determined by measuring the intensity or wavelength of the flash signal.

Advantages of Fluorescent Fiber Optic Temperature Sensor

1. In terms of accuracy
Fluorescent materials are particularly sensitive to temperature changes, which enables fiber optic fluorescent temperature sensors to have high measurement accuracy and meet the needs of many measurement scenarios that require high temperature accuracy. For example, precise control of reaction temperature in scientific experiments and monitoring of patient temperature in the medical field require accurate temperature measurement, and this sensor can effectively undertake such tasks. In certain specific application scenarios, its accuracy can reach a precision level of ± 0.05 ℃ or even higher.

2. Response characteristics
The sensor has a fast response speed and can monitor temperature changes in real time and respond immediately. This feature is particularly useful in scenarios with rapidly changing temperatures, such as overload monitoring in power systems and the need to promptly detect temperature changes in areas where heat is suddenly generated during industrial production processes to prevent potential safety hazards.

3. Distributed measurement capability
It is possible to monitor the temperature of multiple locations simultaneously through a single optical fiber. It can be imagined that if temperature monitoring is carried out at multiple points inside a large engineering structure such as bridges, tunnels, etc., only one fiber optic cable is needed to complete the task. This not only saves costs, but also enables real-time and comprehensive judgment of the temperature status of the overall structure in different parts. Moreover, it can measure temperature on the same optical fiber and may also have other functions such as data transmission, greatly improving the efficiency of fiber optic systems.

4. Anti interference characteristics
Not affected by interference signals, able to work normally in complex electromagnetic environments. In some industrial environments with strong electromagnetic fields (such as power substations) or inside electrical equipment (such as switchgear, etc.), traditional temperature sensors (such as thermocouples, thermal resistors, etc.) generate induced currents in the electromagnetic field due to the measurement probes and wires made of their own metal materials. This current, due to skin effect and eddy current effect, can raise their own temperature, interfere with temperature measurement results, or make measurements unstable. The fluorescent fiber optic temperature sensor uses fiber optic transmission of optical signals, which are completely unaffected by electromagnetic interference, ensuring accurate and stable measurement.

5. Long term stability
Fluorescent materials have strong durability and stability, allowing sensors to maintain high performance stability over long periods of use. In situations where long-term uninterrupted temperature monitoring is required, such as during long-term scientific research experiments or temperature monitoring during the life cycle of some key industrial equipment, it can ensure stable and accurate temperature data collection for a long time without frequent calibration or sensor replacement.

6. Environmental temperature adaptability
Suitable for a wide range of environmental temperatures, effective measurements can be taken from as low as minus Baidu to as high as several hundred degrees Celsius. It can play a role in both low-temperature special experimental environments (such as temperature measurement related to ultra-low temperature superconducting experiments) and high-temperature industrial processing environments (such as metal smelting, etc.).

7. Flexibility and Scalability
Fluorescent materials for sensors can be selected and designed according to actual needs to meet the requirements of various specific application fields. As long as the fluorescent material is adjusted or replaced, it can adapt to different application scenarios. For example, in the medical field, targeted designs can be made for different human body parts or special environments of different medical devices.

Comparison between Fluorescent Fiber Optic Temperature Sensor and Other Optical Temperature Sensors

1. Comparison with infrared temperature sensors
Differences in working principles
Fluorescent fiber optic temperature sensor is based on the temperature fluorescence characteristics of fluorescent materials, and achieves temperature measurement by measuring the lifetime or intensity of fluorescent afterglow, as well as changes in wavelength; Infrared temperature measurement utilizes the principle that the infrared radiation energy of an object changes with temperature, and obtains temperature information by measuring the infrared radiation intensity of the target.
For example, when measuring the temperature of a metal block that is being heated, a fluorescent fiber optic temperature sensor needs to place the optical fiber close to or connected to the surface of the metal block (with contact and non-contact installation methods), and use the changes in the fluorescent substance inside to measure the temperature; The infrared thermometer directly receives the infrared radiation emitted by the metal block for temperature measurement without the need for contact with the metal block.
Differences in accuracy and sensitivity
Infrared temperature measurement is greatly affected by factors such as target surface emissivity, ambient temperature, and measurement distance, and its accuracy and sensitivity are relatively unstable. For some medium and low temperature measurement scenarios, there may be significant errors; The measurement accuracy of fluorescent fiber optic temperature sensors is relatively higher, because the sensitivity of fluorescent materials to temperature allows them to detect temperature changes more accurately, and in the mid to low frequency range, fluorescent fiber optic temperature sensors can maintain good measurement performance.
For example, in a temperature monitoring scenario inside a chemical reaction vessel with small temperature fluctuations and high precision measurement requirements, the accuracy of the fluorescent fiber temperature sensor can be controlled within a small range, while the accuracy of infrared temperature measurement is difficult to guarantee due to factors such as the surrounding environment of the reaction vessel and the optical properties of the vessel itself.
Adapt to the differences in scenarios
Infrared temperature measurement is suitable for non-contact and rapid temperature measurement of surface temperature in non low temperature scenarios, but it has a significant impact on the temperature reading of bright or polished metal surfaces, and can only measure the external temperature of objects, making it inconvenient to measure the internal temperature when there are obstacles; Fluorescent fiber optic temperature sensors can not only be used for surface temperature measurement, but also for measuring internal temperature through appropriate methods such as probe insertion. They will not affect the measurement accuracy of some special materials due to interference from optical properties and have strong universality.
For example, infrared temperature measurement can quickly obtain an approximate surface temperature to preliminarily determine the heat dissipation situation when measuring the surface temperature of electronic circuit chip heat sinks. مگر, if it is necessary to measure the internal temperature of the chip or the temperature at the root of the chip with heat sinks, it is not sufficient. Fluorescent fiber optic temperature sensors can achieve high-precision measurement of chips with heat sinks if the fiber optic probe can reach the inside of the chip or if a suitable probe is designed.

2. Comparison with PT100
Differences in working principles and applicable environments
PT100 uses the characteristic of the resistance value of platinum metal changing with temperature to measure temperature, based on the principle of resistance; The fluorescent fiber optic temperature sensor is based on the principle of fluorescence. PT100 is a contact type sensor.
In an environment with electromagnetic interference, the metal components of PT100 can conduct interference such as pulse group interference, radio frequency interference, surges, etc., causing the thermostat to malfunction or be damaged; Fluorescent fiber optic temperature sensors, due to the use of fiber optic transmission of optical signals, are less affected by electromagnetic interference and can be used in high voltage and strong electromagnetic interference environments, such as transformer interiors, switchgear, وغیرہ.
For example, in the temperature monitoring inside the distribution cabinet of a high-voltage substation, if PT100 is used, due to the electromagnetic interference generated by various electromagnetic devices inside the distribution cabinet, the temperature measured by PT100 may have significant errors or even damage the sensor due to interference; But using fluorescent fiber optic temperature sensors can accurately and stably measure temperature.
Differences in accuracy and stability
During the use of PT100, as time and environmental temperature change, the resistance of the metal may also be affected by its own and other surrounding physical and chemical factors, resulting in slight changes in the resistance temperature relationship, which affects the accuracy and stability of the measurement; After special treatment, the fluorescent material of the fluorescent fiber temperature sensor has stronger stability and is not easily affected by external factors (except temperature). Its accuracy is more advantageous than PT100 in complex environments.

3. Comparison with distributed fiber optic temperature measurement system

Different working principles
Fluorescence fiber temperature measurement is based on the principle of fluorescence lifetime afterglow to measure temperature. It requires fixing the fluorescence fiber on the surface of the measured object and exciting it with a light source to measure the fluorescence lifetime and other parameters emitted by the fluorescence fiber. Then, the temperature of the measured object is calculated based on these parameters; Distributed fiber optic temperature measurement utilizes the inherent characteristics of optical fibers to measure temperature through internal reflection and scattering. It usually involves laying optical fibers around the object being measured and exciting the fibers with light sources such as lasers or LEDs. Then, based on the scattering and reflection characteristics of the internal optical signals of the fibers, the temperature of the object being measured is calculated.
Measurement application scenarios focus on different aspects
Fluorescent fiber optic temperature measurement is usually suitable for measurement occasions that require insulation and high voltage resistance in electromagnetic interference environments, such as high-voltage switchgear, transformers, microwave electromagnetic environments, وغیرہ. Because it can stably measure through the characteristics of fluorescent materials in such environments and does not interfere with equipment, وغیرہ; Distributed fiber optic temperature measurement is suitable for situations that require long-distance, continuous, and high-precision temperature monitoring of the object being measured, such as temperature monitoring of building structures such as oil and gas pipelines, tunnels, bridges, etc., because it can use scattering reflection to monitor continuous temperature changes over long distances along the fiber optic cable.

How to choose the best fluorescent fiber optic temperature sensor

1. Consider the requirements of the application field
Adapt to special environmental requirements
When there are special situations such as strong electromagnetic/radio frequency interference, flammability, explosiveness, corrosion, وغیرہ. in the working environment, fluorescent fiber optic temperature sensors have unique advantages. For example, in the petrochemical industry, there are complex chemical substances that may corrode sensors. It is very important to choose sensors that can resist corrosion and work safely in this potentially explosive safety risk environment. The fiber probe and fiber itself of the fluorescent fiber optic sensor can withstand high voltage and some chemical corrosion without generating ignition sources such as electric sparks, thus meeting the temperature measurement requirements of this special environment. The temperature measurement environment of downhole equipment in oil extraction belongs to this category.
If the working environment is limited by small installation space, it is necessary to choose fiber optic probes and fibers of appropriate size. Fluorescent fiber optic temperature sensors can be made into smaller probes, and the fibers have strong flexibility and plasticity, making them easier to install in small spaces compared to other traditional sensors, such as temperature monitoring of heating parts inside some microelectronic devices.
High precision, sensitivity, and stability requirements
In some scientific research experiments, such as high-precision physics experiments and biochemistry experiments, the accuracy control of temperature is very strict, so it is necessary to choose fluorescent fiber temperature sensors with high accuracy, such as sensor products with accuracy of ± 0.05 ℃ or ± 0.1 °C. ایک ہی وقت میں, if the experiment lasts for a long time, such as several days or even weeks for certain biochemical reactions, the stability of the sensor and the sensitivity of the measurement (which can quickly and accurately capture small temperature fluctuations) are also crucial. This requires the selection of sensors that use high-quality fluorescent materials and have good signal processing systems to ensure that the measurement will not produce errors due to environmental temperature fluctuations or material fluorescence performance degradation.
In some high-end manufacturing industries, such as parts processing in the aerospace field, corresponding temperature monitoring equipment also requires high-precision and long-term stability of sensors.

2. Determine the measurement method and measurement range
Determine sensor type based on measurement points
If there are fewer measurement points (usually less than 50), a single point fluorescent fiber optic temperature sensor can be used. Single point sensors have relatively low costs in this situation and are easy to flexibly layout and install for each individual measurement point. For example, temperature monitoring of several special experimental equipment in a small laboratory only requires installing sensors separately for these devices.
When there are more than 50 measurement points, the overall cost of using a single point sensor will be very high, and the wiring will be very complex. In this case, a distributed fiber optic temperature sensor system or other more suitable methods for large-scale multi-point measurement can be considered (if the overall accuracy requirements are not so high and a certain degree of substitution is allowed). There are hundreds or thousands of servers in a large data center room, and if temperature monitoring is required for some server locations, a large number of measurement points are needed. If single point sensors are used, the cost-effectiveness is extremely low.

Measuring temperature range

Select based on the actual measured temperature range. The temperature measurement range of fiber optic sensors is divided into four sections:- 40°C- +80°C；- 40°C- +250°C；- 40C – +400°C；+ 20C -+600 °C (طبی). For example, a sensor with a temperature range of -40 °C -+80 ℃ may be sufficient for ordinary indoor temperature monitoring; But for high-temperature scenarios such as industrial furnaces or aircraft engine testing, sensors that can measure high temperature ranges such as -40 °C -+400 ℃ or even higher are needed.
3. Probe performance related
The working type of the probe
For immersion probes, they can be used to measure the temperature of solids, liquids, and gases, such as temperature measurement in industrial liquid tanks. This probe has undergone special treatment, and its optical fiber has strong strength and toughness, which can resist chemical corrosion in liquid tanks. For example, measuring the temperature of reactants (which may be a mixture of liquid, solid, and gas) in a chemical reactor is very suitable.
Contact type probes are specifically designed to measure the temperature of object surfaces, such as temperature monitoring for high-voltage equipment such as dry-type transformers, high-voltage switchgear, and high-voltage busbars. It can be well attached to the surface of the device to accurately transmit temperature to the inside of the sensor for measurement.
Medical probes are specially designed for life science measurements, with small and thin probes that, when paired with dedicated demodulation devices, can achieve fast response speeds and very high accuracy. Used in the medical field, such as high-precision temperature detection scenarios for small tissues or local areas within the human body.
The size of the probe and the length of the optical fiber
Select the probe size (diameter) and fiber length based on the requirements of the measurement object and environment. The probe diameter is usually 0.5mm; 0.5 – 1mm； 2.3mm； 3.2mm, وغیرہ. The standard fiber length is 2M, but most can customize the probe fiber length and fiber extension cable length according to needs. If the measurement space is narrow, it may be necessary to choose a smaller diameter probe and customize the fiber length according to the actual installation space. To measure temperature at small gaps in electronic components, a small diameter probe should be used and the fiber length should be customized according to the depth of the gap; If measuring temperature inside large mechanical structural components, a longer fiber length is required to extend to the core area that needs to be measured.

4. Other performance parameters of the equipment
Accuracy and Resolution
When precision and resolution are required, the temperature measurement accuracy of fiber optic sensors is usually divided into five levels: ± 0.05 °C; ±0.1℃； ±0.3℃； ±0.5℃； ± 1 °C. If high-precision temperature measurement is required, such as internal temperature monitoring in certain high-precision optical instruments or high-precision temperature monitoring or cell preservation devices in medicine, sensors with high accuracy and resolution, such as sensors with an accuracy of ± 0.05 ℃ or ± 0.1 °C, need to be selected; If the precision requirements are not so high, sensors for indoor temperature monitoring with an accuracy of ± 1 ℃ can also meet the requirements.
sampling frequency
The sampling frequency of fiber optic sensor temperature measurement system is usually divided into four levels:= 10Hz； 20Hz； 1kHz； 200kHz. When monitoring rapidly changing temperature scenarios, such as monitoring the hot spot temperature inside a high-speed motor, a high sampling frequency (e.g. 1kHz or 200kHz) is required to capture temperature changes in a timely manner to prevent overheating emergencies; For some scenarios with relatively slow temperature changes, such as ordinary indoor temperature monitoring, selecting a sampling frequency of 10Hz or 20Hz can meet the requirements.
Signal output interface
Signal output is divided into analog output and digital output. In an automated industrial control system, it is more suitable to choose sensors with digital output interfaces for direct data acquisition and analysis through devices such as computers, so that digital signal transmission and processing can be carried out without signal conversion; If some traditional instrument control systems may only support the reception of analog signals, then the analog output interface can be directly connected to the instrument equipment for display and simple control.
Installation form of detector
Signal demodulator mainly comes in handheld portable and fixed forms, with or without display. Fixed products include industrial standard DIN rail installation, PCB board, ordinary desktop, and standard industrial cabinet type. If it is a temporary outdoor use to detect the temperature of several points inside a large device, it can be handheld, portable, flexible to move, and easy to operate and arrange for detection; If monitoring the long-term stability and operating temperature of a large production line equipment, it is necessary to choose a fixed and suitable industrial environment, such as DIN rail installation or cabinet installation, which can be easily connected to the production line automation monitoring system.

5. Consider cost-effectiveness
Due to the fact that various types of fiber optic sensors are relatively new technology products with generally high prices, users usually need to make a choice between product performance/functionality and price. Firstly, determine your minimum performance requirement baseline, and then compare factors such as price among product lines that can meet this baseline requirement.

For example, if there are three different brands of fluorescent fiber optic temperature sensors, Product A has an accuracy of ± 0.1 °C, high resolution, and good anti-interference ability, with a price of 1000 yuan; The precision of product B is ± 0.3 °C, slightly inferior in anti-interference ability, and the price is 800 yuan; The precision of product C is ± 0.5 °C, which basically meets the anti-interference requirements of the usage environment. The price is 600 yuan. If precision and anti-interference are highly valued and the budget is sufficient, product A can be chosen; If the precision requirement is not extremely high and the budget is limited, then C product is also an option.

Application Case of Fluorescent Fiber Optic Temperature Sensor

1. In the field of power grid
Temperature monitoring is crucial in the power grid. Fluorescent fiber optic temperature sensors have the characteristics of high accuracy and fast response, which can accurately monitor temperature changes in industrial production processes. For example, in equipment such as switchgear and transformers, fluorescent lifetime fiber optic temperature sensors can monitor the temperature of critical connection points, detect temperature anomalies in a timely manner, and prevent overheating and arc accidents. Traditional temperature sensors may read inaccurately in such high voltage environments due to electromagnetic interference, but fluorescent fiber optic sensors are not affected by such interference and have high reliability. اضافی طور پہ, high temperatures in transformers may cause insulation material aging and lead to faults. Fluorescent lifetime fiber optic temperature sensors can be installed in the oil or near the windings of transformers to monitor temperature, ensuring normal operation and extending their service life.

2. Medical field
In magnetic resonance imaging (MRI) ٹیکنالوجی, superconducting magnets need to be cooled to extremely low temperatures. Fluorescent lifetime fiber optic temperature sensors can be used to monitor the performance of cooling systems and ensure that magnets are at the correct temperature. Due to the presence of strong magnetic fields in the MRI environment, traditional electronic temperature sensors may be subject to interference or damage, while fiber optic sensors do not have these issues. اضافی طور پہ, fluorescent lifetime fiber optic sensors can also be used in clinical medicine, such as monitoring patient temperature during temperature monitoring or thermal therapy, to ensure safe and effective treatment. Due to their high precision and fast response, they are suitable for situations that require strict temperature control.

3. Energy management
In the energy industry, fluorescent fiber optic temperature sensors can be used to monitor the operating temperature of power equipment and systems, ensuring the safe and efficient utilization of energy.

In summary, fluorescent fiber optic temperature sensors play an important role in multiple fields due to their high precision, fast response, long-term stability, and resistance to electromagnetic interference. With the continuous development of technology, their application prospects will become even broader.