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Harsh environment of anti-polarization optical fiber temperature sensor
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1 Introduction
Fiber-optic temperature sensor as a new type of temperature sensor, with high measurement accuracy, anti-electromagnetic interference, safety explosion-proof, fire-resistant insulation and many other advantages, in many special occasions have been widely used. Therefore, the fiber-optic temperature sensor research and development has been the field of fiber-optic sensor, one of the hot and difficult. Especially in the power systems, power generation, transmission and power distribution systems are accompanied by poor magnetic and temperature environment (such as high radiation, high voltage, etc.), so by the insulating material made of fiber-optic sensors on the power system measurement and monitoring of the parameters from an important role. Many research institutions are committed to the development of practical application of optical power sensors, some have been a successful trial. LUXTRON company has successfully developed for large-scale monitoring of transformer winding hot spot temperature of the fiber-optic sensors, the system in the -30 ~ 200 ℃ within the measurement accuracy of ± 2 ℃, the use of the sensors, the realization of the transformer in the research and development, life expectancy estimates and dynamic load temperature management in the process of detection and measurement of temperature field. To further improve accuracy, this paper presents an accurate temperature sensing technology, and for large-scale multi-point temperature of the transformer needs to monitor the development of a multi-channel fiber-optic temperature sensor.
2 the basic principles of
Figure 1 for the fiber-optic temperature sensor schematic diagram, which is wide-spectrum light source, coupler, high extinction ratio of optical fiber polarization, and transmission fiber (UNCED), temperature and optical power meter sensor head component. Among them, the transmission optical fiber for polarization maintaining fiber, mainly used to connect devices and sensor bias from the first. Sensor head for a small section of optical fiber, optical fiber transmission and optical fiber sensor head of the stress into a 45 ° angle between the main axis (enlarged part of Figure 1). At the other end of the first sensor, there is total reflection-plated dielectric film. In the process of optical transmission, polarization mode coupling process in Figure 2, Y axis, said slow axis, X axis, said fast axis, the representative of the polarization direction of the arrow. Wide-spectrum light source through the coupling and after polarizer polarized light and along the optical fiber transmission, the cross-section in Figure 2 in 1. Fiber-optic transmission link with the sensor head point, the two polarization maintaining fiber stress axis into 45 ° angle, optical sensing will be among the first in the two polarization eigen-mode, cross-section in Figure 2 in 2. Reflected light along the same route to return to again reach the point, each polarization mode optical fiber in transmission also stirred up the other two orthogonal polarization mode, the cross-section in Figure 2 in 3. Four different polarization mode phase: YY"X, YY"Y, YX"X, YX"Y continue to optical fiber transmission, upon arrival at the polarizer, only with the polarizer parallel to the direction of pass-ray polarization mode YX"Y can YY"Y and eventually reach the optical power juice, cut-off in Figure 2 and 4. The phase difference for
△ β for the two main optical fiber transmission polarization axis deviation constant, L for the first polarization maintaining fiber-optic sensor length, δ polarization only produced the first fiber-optic sensor. Output signal to interference
Where, K to reach the detector and the light intensity factor, γ (δ) is a wide-spectrum light source coherence function. For polarization maintaining fiber, such as pandas or tie type, is set in the coating layer structure to achieve the polarization stress maintained. Study shows that: △ β -200 ~ +400 ℃ in temperature increases with the linear decrease in the number of the linear coefficient of about 10-3 level, a negative sign, and the length of optical fiber changes with temperature linearly relationship between the temperature coefficient of about 10-6 weight, can be ignored. Therefore, δ can be written as
Where a0, a1 is the model coefficient can be obtained through the calibration experiment; T for which the ambient temperature sensor. Slave (3) we can see that by measuring the intensity of light output can be identified to interfere in fiber-optic temperature-sensitive, but also by changing the length of optical fiber to adjust the measuring range and sensitivity.
3 Experimental Study
Based on the structure shown in Figure 1, the experimental system set up. Light source for an average of 1300 nm wavelength of the SLD broadband light source, spectral width 30 nm; transmission fiber is the Panda type polarization maintaining fiber; sensing the length of the first random access to 11.3 mm. Optical Power Meter to interfere with the output power measurement, the actual temperature measured by the thermometer, the measured data can be recorded by computer in real time. In the -45 ~ +65 ℃, output power and temperature curve in Figure 3.
Changes in the magnitude of the signal interference due to coherence function γ (δ) of δ caused by the temperature dependence of, in order to make a simple fitting process, it is assumed that γ (δ) is a linear change, according to type (3), may have the following objectives function
To test data for samples (4) as the goal, fitting curve in Figure 3, the model coefficients as listed in Table 1. c1 represents the γ (δ) and temperature; a1 is the temperature coefficient of sensor head; c2, c3 is the deviation value. As can be seen from Figure 3, measurement curve and fitting curve coincide well in the vicinity of the peak error is γ (δ) of the error caused by linear model.
In order to verify the stability of a prototype sensor, the sensing head placed in ice water to form a mixture of the constant 0 ℃ environment, measuring changes in output. From Figure 3 can be seen at 0 ℃, the output power of about 324μW, close to the temperature sensitivity of the largest coefficient of 46.71μW / ℃. Figure 4 for the time and optical power output curve, measurement time is about 30 min, sampling interval 1 s. Statistics show that the standard deviation of optical power 0.45μW, the corresponding temperature change for 0.0096 ℃.
More than 4-channel temperature sensor
In large power transformer, it is necessary to monitor the temperature of all the possible hot spots, so multi-channel temperature sensor system is necessary. In addition, because fiber-optic parts are placed in hot oil in the transformer, the sensor must be made to meet the high-voltage insulation, anti-high temperature above 250 ℃, heat the oil requirements.
4.1 Sensor program
8-channel fiber-optic temperature sensing system as shown in Figure 5, light source using a high-power erbium-doped fiber light source, its output power is greater than 10 mW, the average wavelength of 1545 nm, spectral width of 31 nm. 1 × 9 single-mode fiber optical power splitter will be divided into 9 equal parts, one of which channel to monitor changes in light source; other 8 as 8-channel temperature sensing of the light source, each channel using the structure shown in Figure 1 . The first reflection from the sensor 8 of the optical signal received by the photodetector, the output of detector 9 through the A / D converter digitized. First of all, the microprocessor calculates the temperature according to the value of the model solution, and then to the display module to show that at the same time with the computer through the RS232 serial port for real-time communications. Sensing in part by the polarizer, 2 m long polarization maintaining fiber-optic transmission and sensing head, of which the polarizer extinction ratio higher than 28 dB, insertion loss of less than 0.8 dB. Sensing part and the light source / detection part 8 through the 100 m single-mode fiber optic cable to connect the core to achieve long-range measurement.
4.2 Sensor Head production and packaging process
In applications, optical fiber and sensor head was placed in the hot oil in the transformer. Therefore selection of silica gel packages Panda Polarization Maintaining Fiber-type resistance to ensure that the high temperature above 250 ℃. This shot of polarization maintaining fiber length 1.9 mm, loss 1.1 dB / km, a diameter of 250μm. Figure 6 for the sensor head and its package diagram. Figure 6 (A) for 8-channel sensing of each road by the FC connector, optical fiber polarizer, 2 m long Panda type polarization maintaining fiber and about 0.5 mm long optical fiber sensor head component . Quartz fiber-optic sensor head capillary seal, the rear package in Figure 6 (B) as indicated. Figure 6 (C) shows a diameter of 125 μm bare fiber sensing head and deposited on the end of the reflective optical film. The use of inner diameter of 319μm, diameter of 436 μm to protect the capillary fiber and sensing head, it appeared to面涂have 20 μm thick PMMA film. These are to ensure that the sensor head in the harsh environment with very good electrical insulation and durability.
4.3 linear sensor head model
In style (4), it is necessary to calculate 5 parameters, the temperature calculation process is complex. Through the choice of probe length and precise and accurate cutting process, close to linear relationship between sensor response. After linearization, the Figure 7 (a) gives the sensor head 8 of the response curve. Therefore, the temperature sensor can be obtained through the polynomial fitting. 3 times a polynomial fitting, the objective function for fitting
T = b0 + b1x + b2x2 + b3x3 (5)
Where b0 ~ b3 is the coefficient of the need for model calibration. Figure 7 (b) for the fitting of the temperature after the typical error curve, in the 40 ~ 220 ℃ with the maximum deviation is 0.37 ℃, Figure 7 (c) is based on style (5) model calculation shown in the temperature values, can be seen They showed a good linear relationship.
The results of calibration and test a prototype 4.4
In order to verify the prototype fiber-optic temperature sensor accuracy of measurement in the Great Wall of China Institute of Technology conducted a calibration test, the unit of temperature measurement at the national level units have carried out large-scale, high-precision temperature measurement capacity. Measurement temperature range is from 0 ~ 200 ℃ is divided into intervals of about 20 ℃, a total of 11 measurement points. A typical test error is shown in Figure 8, 8-way sensor measurement error ± 0.5 ℃ in the range.
5 Conclusion
In this paper, a practical optical fiber temperature sensors and related technologies in detail. Developed can be used for power transformer winding temperature monitoring of multi-channel temperature sensor. Use a special coating, packaging and production process of the small size of the development of fiber-optic temperature sensing head, to meet the anti-poor indicators of the environment and the requirements of practical applications.
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* 回复内容中包含的链接未经审核,可能存在风险,暂不予完整展示!Temperature Sensor Types
Big differences exist between different temperature sensor or temperature measurement device types. Using one perspective, they can be simply classified into two groups, contact and non-contact. The two links below take you to descriptive pages on each type with a breakdown by more specific, detailed types under that simple, first breakout.
There are also vendors of each sensor type, some vendors sell more than one type and some sell nearly all types, but not always all brands. There are differences between brands and the differneces are most evident among those device types for which there are few if any recognized standards. Start your search either for a specific temperature measurement device type or go to the vendor page index and you can access the vendors of specific types from there.
Both contact and non-contact sensors require some assumptions and inferences in use to measure temperature. Many, many well-known uses of these sensors are very straightforward and few, if any, assumptions are required.
Other uses require some careful analysis to determine the controlling aspects of influencing factors that can make the apparent temperature quite different from the indicated temperature.
Tell your new product and application stories at The Temperature Community website: www.t********.net or feedback to us and we"ll consider adding it here with your byline!
Remember the truism that all sensor have errors in their readings - all the time. One key secret to high quality measurement results is to have confidence in the error estimates. Neglecting to make a careful error analysis can result in error much larger than the assumed values.
It is worth noting that all competent error analyses start with the uncertainties assigned to the traceable calibration of the sensor itself. Without traceable calibration, one is forced to make assumptions. (You know what the word ass|u|me means, we hope.)
Without traceable measurements, the numerical values of results will always be questionable and hardly worth the effort, and cost. It most often pays to get started on the right path to technically sound measurements by beginning with some understanding of the options involved in selecting a temperature measurement device and then in obtaining one that meets the expected conditions and standards, is calibrated and that the calibration is traceable to either a fundamental standard (e.g. the triple point of water) or a national standard. See our calibration and standards pages for more details on each aspect of sound measurement practice.
Contact Sensors
Contact temperature sensors measure their own temperature.
One infers the temperature of the object to which the sensor is in contact by assuming or knowing that the two are in thermal equilibrium, that is, there is no heat flow between them.
Noncontact Sensors
Most commercial and scientific noncontact temperature sensors measure the thermal radiant power of the Infrared or Optical radiation that they receive from a known or calculated area on its surface, or a known or calculated volume within it (in those cases where the obect is semitransparent within the measuring wavelength passbad of the sensor).
One then infers the temperature of an object from which the radiant power is assumed to be emitted (some may be reflected rather than emitted). Sometimes the inference requires a correction for the spectral emissivity (NB: the two words, spectral & emissivity, are used together in correcting IR Thermometer readings -the "emissivity", unspecified, is a big trap which even some of the suppliers of devices and calibration equipment fall into unwittingly for a variety of reason about which one can only speculate ) of the object being measured.
Knowing how and when to apply a spectral emissivity correction is part of the inference, too, and can introduce significant errors if not done correctly. See our Trip down the E-missivity Trail to help you understand that aspect a little better.
Dewpoint Temperature
-- Humidity--
Although this area is in reality just an application of temperature sensors and other sensors, it grew out of temperature measurements.
Remember the old style humidity indicators that consisted of two little glass thermometers, the wet and dry bulb thermometers with a little look up table that told you the humidity, both absolute and relative? Have a look, it"s a very important area in terms of human comfort, food safety and energy conservation and efficiency in thermal processes.
Thermal Imaging
The special world of thermography and thermal images includes the temperature-measuring kind of thermal imagers called "Radiomatic", by those in the business, and "Quantitative" by those mostly in R&Dwith thermal imaging. Then, too, there are those who call it "Thermology" when it applies to measurements made on the human body and "Medical Thermography" by still others, some even in the same business.
Users of infrared thermal imaging have many options in cameras both with and without temperature scales or temperature indication.
It seems really odd to have all these different names kicking about, when they all refer to the same basic technology. The names seem to differ only by application area. In reality, they all work because of the same Law of Physics, called Planck"s Law.
That"s the same law that describes how IR thermometers, optical pyrometers, radiation thermometers and infrared intrusion or people detectors work (note the common trait of multiple names).
The only thing that an IR thermal imager of any denomination really does is take the output from an infrared detector, or plethera of detectors, and presents a 2-D scan of the infrared intensity distribution in the field of view of an optical system. These devices could be called by one common name. The devices that provide temperature information, probably more than any other type of device should be called Infrared Imagers, or Thermal Infrared Imagers or, simply, Thermal Imagers.
Go to our thermal imaging section by clicking the above underlined link and learn more than you ever thought you would want to know about the subject.
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Click here to find out about ISPoT!
The Applications page can lead you to many well-known solutions or examples, possibly similar to the one you are trying to solve. Why re-invent the wheel?
Two excellent reference by Baker et al. are listed in the References page and worth reading to get an idea of the complexities that can arise, how to test and get around them. They are older books and while the technology of the equipment has changed, especially the electronics, the measurement fundamentals have not. Heat flow is heat flow and thermal radiation physics was unified theoretically by Max Planck more than 100 years ago!
A great many temperature measurement problems are solved through a good understanding of the heat flow involved in a specific measurement situation.
Surface temperature problems with contact sensors are often best solved in many cases through the use of non-contact sensor. They are in use in many industrial plants worldwide in great numbers. The above reference texts provide interesting analyses of the likely errors making contact temperature measurements of surfaces, both stationary and moving surfaces. We have not seen any recent analyses with as much detail!
Good luck and best wishes.
参考:
http://www.t**********.com/sensors.html
http://www.ruhr-uni-bochum.de/rubitec/Schweiger_engl.pdf