A Study On Space Resolution And System Stability Of Distributed Optical Fiber Raman Temperature Measurement System

The distributed optical fiber temperature measurement system based on Ramanprinciple was proposed up at the age of seventy in the twentieth century. Compared withtraditional temperature measured system, the distributed optical fiber Ramantemperature measured system (DOFRTS) has lots of obvious advantages, such asanti-electromagnetic interference, wide measure area, well stability, low cost and easierinstallation. Therefore, more and more people are making more and further study for it.In the past ten years, the perfect theory of DOFRTS has been built up. Many matureproducts have been launched on the market. Now, because of these special advantages,the DOFRTS are been applying widely in national defense, industry, public safety andother fields.Because the foreign researchers that study the technology of DOFRTS is earlierthan that in our domestic, it leads that the parameter index of DOFRTS made in China isrelatively backward. It is generally in system stability, space resolution and otheraspects. So, it is necessary to research a DOFRTS which has good system stability, highspace resolution.In this paper, the historical development of optical fiber sensor is reviewed, andthe principles and characteristics of three different optical fiber temperature sensors arediscussed. By building up the classical molecule model and the quantum mechanicsmodel of Raman scatting, the basic theory of Raman scatting is established. Combinedwith the optical time domain reflection (OTDR) technology, the fundamental principleof DOFRTS is clarified. According to the design requirements, the parameters of systemdevices are analyzed and calculated, and then, system devices are selected and tested.The DOFRTS is built up and the temperature measured experiments (it includes dataacquisition, analysis and processing) is lunched. After making a traditional temperaturecalibration, the DOFRTS achieves temperature measurement.For overcoming the poor inaccuracy of measurement(about±2℃), this paperanalysis the main influence factors at first, and then a new dynamic multi-sectiontemperature calibration method is proposed up, a dynamic multi-section temperaturecalibration module is made, applying it in DOFRTS at last. The inaccuracy ofmeasurement is promoted up to±1℃. Because of deficient bandwidth, the system spaceresolution is low. When the sensing length of fiber is close to space resolution, there is not an accurate temperature response. For solving the problems, a new linear algorithmis proposed up in this paper. First, the relationship between Raman ratio andtemperature and the characteristics of frequency response are analyzed; and then amathematical model is built up for this algorithm; some related experiment is done byusing the algorithm. The space resolution is promted up to1meter. At last, a systemtesting is finished on temperature resolution, measurement time and system operatingenvironment, the test results meet the design requirements. Therefore, a DOFRTS whichhas good system stability, high space resolution and distinct advantage of price issuccess developed.