Advances in Measurement Systems Part 3 doc

AdvancesinMeasurementSystems76 the guidance force changes. The experimental results of the guidance forces are not better than that of the levitation forces. The most changes of measured guidance forces in the 48 s time frame were 0.28 N at 300 rpm and 0.79 N at 400 rpm). 6. Conclusion Three high temperature superconducting (HTS) Maglev measurement systems were successfully developed in the Applied Superconductivity Laboratory (ASCLab) of Southwest Jiaotong University, P. R. China. These systems include liquid nitrogen vessel, Permanent Magnet Guideway (PMG), data collection and processing, mechanical drive and Autocontrol features. This chapter described the three different measuring systems along with their theory of operations and workflow. The SCML-01 HTS Maglev measurement system can make real time measurement of Maglev properties between one or many YBCO bulks and employ a PM or PMG. Also the trapping flux of high T c superconductors can be measured in the scanning range of 100 mm×100 mm. It was especially employed to develop the on board HTS Maglev equipment which travels over one or two PMGs. The on board Maglev equipment includes a rectangular-shaped liquid nitrogen vessel and YBCO bulk superconductors. Based on the original research results from the SCML-01, the first man-loading HTS Maglev test vehicle in the world was successfully developed in 2000. In order to make more thorough and careful research investigations, the HTS Maglev, HTS Maglev Measurement System (SCML-02) was subsequently developed with even more function capabilities and a higher precision to extensively investigate the Maglev properties of YBCO bulk samples over a PM or PMG. The new features included: higher measurement precision, instant measurement at movement of the measured HTS sample, automatic measurement of both levitation and guidance forces, dynamic rigidity, ability for the measured HTS sample to be moved along the three principal axes all at once, relaxation measurements of both levitation and guidance forces, and so on. The main specification of the system is: position precision ±0.05 mm. vertical force precision 2 ‰; horizontal force precision 1 ‰; and force measurement precision of 0.02 N. In order to investigate the dynamic characteristics behavior of the HTS Maglev engineering application, an HTS Maglev dynamic measurement system (SCML-03) was designed and successfully developed. The circular PMG is fixed along the circumferential direction of a big circular disk with a diameter of 1,500 mm. The maximum linear velocity of the PMG is about 300 km/h when the circular disk rotates round the central axis at 1280 rpm. The liquid nitrogen vessel with HTS bulks is placed above the PMG, and the vessel is allowed to move along the three main principal axes so that sensors can detect force variations stemming from the superconductors. The design, method, accuracy and results have allowed the successful development of these three measurement systems. All systems are calibrated by standard measurement technology, for which its reliability, stability, featured functions, and precision have also been validated through its long-term usage. HighTemperatureSuperconductingMaglevMeasurementSystem 77 7. Acknowledgements The authors are grateful to Zhongyou Ren, Yiyu Lu, Zigang Deng, Jun Zheng, Fei Yen， Changyan Deng, Youwen Zeng, Haiyu Huang, Xiaorong Wang, Honghai Song, Xingzhi Wang, Longcai Zhang, Hua Jing, Qingyong He, Lu Liu, Guangtong Ma, Wei Liu, Qunxu Lin, Yonggang Huang, Minxian Liu, Yujie Qing, Rongqing Zhao, and Ya Zhang for their contributions towards the abovementioned HTS Maglev measurement systems. 8. References Bomemann H. J., A. Tonoli, T. Ritter, C. Urban, O. Zaitsev, K. Weber, and H. Rietschel, (1995). En g ineerin g Protot y pe of a Superconductin g Fl y wheel for Lon g Term Energy Storage. IEEE Trans. Appl. Supercond., 5(2): 618-621 D’ Ovidio G., F. Crisia, G. Lanzara, (2008). A ’V’ shaped superconductin g levitation module for lift and guidance of a magnetic transportation system. Physica C, vol 468, pp. 1036-1040 Den g Zi g an g , Jun Zhen g , Hon g hai Son g , Lu Liu, Lulin Wan g , Ya Zhan g , Su y u Wan g , and Jiasu Wang, (2007). 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IEEE Trans Appl Supercond, 17(2): 2103-2106 AutonomousMeasurementSystemforLocalization ofLoss-InducedPerturbationBasedonTransmission-ReectionAnalysis 81 Autonomous Measurement System for Localization of Loss-Induced PerturbationBasedonTransmission-ReectionAnalysis VasilyV.Spirin X Autonomous Measurement System for Localization of Loss-Induced Perturbation Based on Transmission-Reflection Analysis Vasily V. Spirin División de Física Aplicada, CICESE, Apdo. Postal 2732, CP 22860, Ensenada, B.C. México 1. Introduction The highest state of the art in optical sensing is achieved with optical fiber distributed sensors that allow the measurement of a desired parameter along the test fiber (Hartog, 2000; Byoungho Lee, 2003). The regions where perturbations occur are usually localized by means of optical time-domain reflectometry (OTDR) or frequency domain reflectometry (OFDR) (Tsuji et al., 1995; Pierce et al., 2000; Venkatesh et al., 1990). All these methods utilize time- or frequency-modulated light sources that allow us to localize a number of perturbations along the test fiber simultaneously. Meanwhile, for some applications, it is important to detect and localize a rare but hazardous alarm condition which typically occurs as a single infrequent event, such as a pipe leak, fire or explosion. For such applications, we proposed a novel simple and inexpensive measurement technique based on so-called transmission-reflection analysis (TRA) (Spirin et al., 2002a). Generally, the TRA method is based on the unique relationships between normalized transmitted and Rayleigh backscattered powers for different locations of the loss-induced disturbance along the sensing fiber. The TRA technique utilizes an unmodulated light source, power detectors and a sensing fiber. Localization of a strong disturbance with a maximum localization error of a few meters along a few km-long single-mode sensing fiber was demonstrated (Spirin et al., 2002b). The paper presents a systematical review of our works in the TRA-sensing area. In the first parts of the paper we describe general ideas of the TRA, including principle of the operations of TRA-based sensors, localization errors examination, a transmission-reflection analysis for a distributed fiber-optic loss sensor with variable localization accuracy along the test fibre, and theoretical and experimental evidences that the TRA method can be modified for detection and localization of a number of perturbations that appear one after another at different positions along the test fiber. In the final part we offer completely autonomous measurement system based on transmission-reflection analysis (AMS-TRA). This part includes design of the AMS-TRA system, thermal stability inspection, detailed analysis of experimental accuracy and localization errors, and implementation of the system for gasoline leak detection and localization. 4 AdvancesinMeasurementSystems82 2. Single Perturbation Localization The basic idea of the TRA method is to localize the perturbation by using the unique relationships between normalized transmitted and Rayleigh backscattered powers of an unmodulated CW light source for different locations of the loss-induced disturbance along the sensing fiber. Indeed, if the bending losses occur at the remote-end of the sensing fiber (see Fig.1), an increase in the load leads to a proportional decrease of the transmitted power. However, it does not change the Rayleigh backscattered power, because all fiber length participate in backscattering and the launched power is the same such as for undisturbed fiber. t 1 r 1 r 2 l 1 light source L source-end remote-end Fig. 1. Test fiber configuration for single perturbation; l 1 – perturbation location, t 1 – transmission of loss-inducing segment, r 1 , r 2 – reflections from source- and remote-ends, L- test fiber length. But if we bend the sensing fiber close to the source-end, the decrease in transmitted power is accompanied by a decrease in the Rayleigh backscattered power. Because in this case the launched into the fiber power is decreased and backscattered power is also decreased due to the induced losses. Further, if we bend the sensing fiber in the middle, the first half of the fiber, which is closer to the source-end, scatters the light as well as half of undisturbed fiber, but the power scattered from the second half is less due to losses induced in the middle. So, for the identical loss-induced perturbations the value of the decrease in normalized backscattered power depends on the location of the excess loss region. To find an analytical expression for calculation of the distance from the fiber source-end to the location of the loss region, we will analyze the configuration with two plain fiber sections whose lengths are l 1 and L-l 1 respectively, and a short fiber piece between them affected by a monitored condition (see Fig.1). Plain fiber sections possess Rayleigh scattering and attenuation due to light absorption and short fiber piece induces a losses. The power reflection coefficient of each Rayleigh scattering fiber segment can be calculated as (Gysel & Staubli, 1990; Liaw et al., 2000): (1) where  s is the attenuation coefficient due to Rayleigh scattering,  is the total attenuation coefficient of the test fiber,  l i is the length of the i-th fiber segment, and recapture factor S for the fiber is defined as (Brinkmeyer, 1980): (2) , )]2exp(1)[2/()( isi lSlR      , /)( 2 1 2 2 2 1 nnnbS  AutonomousMeasurementSystemforLocalization ofLoss-InducedPerturbationBasedonTransmission-ReectionAnalysis 83 where b depends on the waveguide property of the fiber and is usually in the range of 0.21 to 0.24 for single-mode step-index fiber (Brinkmeyer, 1980), n 1 and n 2 are the refractive indices of the fiber core and cladding, respectively. Introducing a parameter S  = S(  s /2  ), the transmission and backscattering coefficients of plain fiber sections can be written as T i = exp (  l i ) and R i = S  (1-exp(-2  l i ), respectively. The short fiber piece is affected by monitored conditions which introduce additional light losses. A transmission of short fiber piece is t 1  1. Let us assume that the scattering is relatively weak and the portion of the scattered light is very small. This allows us to simplify the analysis, neglecting multiple scattering in both directions. The reflections with coefficients r 1 and r 2 from the fiber source- and remote-ends, respectively, have to be taken into account because even a weak reflection can be comparable to the back scattering. However, we can assume that r 1,2 << 1 and neglect multiple reflections as well. In this case, the transmission T and back-scattering R coefficients of this optical system can be written as: (3) (4) Normalized transmitted T norm and backscattered R norm coefficients are defined as: (5) (6) where T max is the maximum transmittance of initially undisturbed sensing fiber when t 1 =1, (7) and R max is the maximum back-scattering coefficients of undisturbed optical system (8) The relationship between the normalized transmitted T norm and Rayleigh backscattered R norm powers for single perturbation can be expressed from (5-6) as: (9) To localize the perturbation with the proposed method, we need to find a parametric curve that passes through the point with coordinates equal to the measured normalized Rayleigh   L erSrSR   2 21max )( , e - max L T   , e - 1211 L tTtTT   .)1()1( 2 2 2 2 1 2 1 )(2 2 1 2 1 2 1 11 rTtTeStTeSrR lLl       , 1 max t T T T norm  , )( )1()( 2 21 2 2 1 22 121 max 1 L l L norm erSrS etSetrSrS R R R             . )( )()1)(( 2 2 2 2 2 2 21 2 1 1 LL l l L normnorm norm ereeS eSerSRRrS T               AdvancesinMeasurementSystems84 backscattered and transmitted powers. The location of the loss region can also be found directly from Eqn. (9) as: (10) Therefore, the measurement of the normalized transmitted and backscattered powers, as well as the knowledge of the fiber attenuation coefficients  and  s , provide the calculation of the distance l 1 from the fiber source-end to the fiber section with induced losses. The slope of dependence of normalized backscattered power R norm versus the square of normalized transmitted power T 2 norm can be found from Eqn. (9) as: (11) As we can see this slope uniquely depends on perturbation location l 1 . Therefore, the location of the single perturbation can be found from experimentally measured slope as: (12) The relationship between normalized Rayleigh backscattered power R norm and the square of normalized transmitted power T 2 norm is almost linear for a single perturbation which affects the test fiber in any location (see Eqn. (9)). Fig.2 shows the result of the numerical calculation of these relationships when additional losses occur at distances l 1,n = n  l from the source- end of the test fiber, where n = 0,1…10, and the interval between bending locations  l = 284.4 meter. Transmitted and backscattered powers were normalized with respect to their initial undisturbed values. A typical value for b equal to 1/4.55 for single-mode fibers (Beller, 1998) was used in the calculations. Reflections from the source-end and the remote- end of the sensing fiber, which are respectively equal to 4.7x10 -6 and 1.5 x10 -5 in our experiment, were also taken into account in the calculations. For the verification of the proposed method we use firstly a laboratory experimental setup. The schematic diagram of the TRA based fiber-optic sensor is shown in Fig. 3. A continuous wave (CW) light emitted by a amplified spontaneous emission (ASE) optical fiber source operating near 1550 nm wavelength with a linewidth of few nm was launched into a 2.844 km-long standard single mode SMF-28 fiber through 3 dB coupler. The launched optical power was about 1.1 mW, and the attenuation coefficient of the test fiber, which was measured with OTDR, was equal to 0.19 dB/km. An optical isolator was used to cancel back reflections influence on ASE source. An immersion of all fiber ends was employed in order to reduce back reflections. Standard power detectors were used to measure the transmitted      . )1( ))(())(1( ln 2 1 2 2 2 2 1 1 norm L normnormnorm TS erSTRrSR l     . )( )( )( 2 21 2 2 2 2 2 1 L LL l norm norm erSrS ereeS T R                                    )1 )( ()( )( )( ln 2 1 2 2 2 2 1 1 norm norm L norm norm T R eSr T R rS S l     [...]... Backscattering in SingleMode Fibers”, J Lightwave Technology Vol 8, 1990, pp 561-567, ISSN: 0 733 -8724 Liaw, S.-K ; Tzeng, S.-L & Hung Y.-J (2000) Rayleigh backscattering induced power penalty on bidirectional wavelength-reuse fiber systems, Optics Communications, Vol 188, 2000, pp 63- 67, ISSN 0 030 -4018 Brinkmeyer, E (1980) Backscattering in single-mode fibers, Electronics Letters, Vol 16, 1980, pp 32 9- 33 0,... sensor interrogation Electronics Letters, Vol 38 , No 3, 2002, pp 117-118, ISSN 00 13- 5194 Spirin, V V.; Shlyagin, M G.; Miridonov, S V & Swart, Pieter L (2002b) Alarm-condition detection and localization using Rayleigh scattering for a fiber optic bending sensor 104 Advances in Measurement Systems with an unmodulated light source Optics communications, Vol 205, No 1 -3, 2002, pp 37 -41, ISSN 0 030 -4018... the interval between bending locations l = 284.4 m (,  - experimental results, and solid lines – theoretical dependencies) To induce the bending losses in the sensing fiber, we used bending transducer, which is also shown schematically in Fig .3 By tuning the bending transducer we changed the normalized transmitted power from its initial undisturbed value equal to 1 up to more than -30 dB The bending... is induced A derivative R(z)/z can be interpreted as a differential reflectivity that also has an arbitrary distribution along the test fiber Reflectivity inside the fiber can be induced by Raleigh backscattering or any other way including imprinting of Bragg gratings inside the fiber Taking into account the reflection from the ends of the sensing fiber, total power reflection coefficient of the initially... oil 108 Advances in Measurement Systems Shutter - This device provides a means of cutting off the radiation beam, making the radiation generator safe for handling and operations in the proximity Standards Magazine - This device contains a group of precision (often NIST traceable) samples that can be introduced into the radiation beam (individually or in groups) to provide a means of measuring the emitted... minutes of gasoline influence Initial variation of alarm distance l1 was 32 meters for 0.5 dB losses and then decreasing to ± 13 meters for 2 dB losses For the losses more than 3 dB the variations not exceeds 3 meters Normalized transmitted power 1.0 0.8 0.6 0.4 0.2 0.0 0 50 100 150 200 250 30 0 Time, min Fig 20 Normalized transmitted power during wet-dry cycle ( - gasoline influence, + - drying) Alarm... 33 0, ISSN 00 13- 5194 Beller, J (1998) OTDRs and Backscatter Measurements, In: Fiber Optic Test and Measurement, edited by D Derickson, pp 434 -474, Prentice Hall PTR, ISBN 0- 13- 534 330 -5, New Jersey Spirin, Vasilii V (20 03) Transmission-Reflection Analysis for Localization of Temporally Successive Multipoint Perturbations in a Distributed Fiber-Optic Loss Sensor Based on Rayleigh Backscattering Applied... Rubber Technology, 638 pages, Kluwer Academic Publishers, ISBN 0-412 539 50-0, Netherlands Spirin, V.V.; Shlyagin, M.G.; Miridonov, S V ; Mendieta, F J & López R M (2000) Fiber Bragg grating sensor for petroleum hydrocarbon leak detection, Optics and Lasers in Engineering, Vol 32 , 2000, pp 497-5 03, ISSN 01 43- 8166 López, R.M ; Spirin, V V ; Shlyagin, M.G ; Miridonov, S.V ; Beltrán, G ;.Kuzin, E.A & Márquez... losses induced at different locations with interval l = 284.4 m Every line which is intersecting the measurement- rectangular corresponds to one of the possible local position of the perturbation Therefore the localization error depends on the 92 Advances in Measurement Systems Normalized Rayleigh backscattered power number of the intersecting lines As we can see for very week losses nearly all lines... 14 hours Tnorm 1.005 0.995 2 .39 97 % 0.985 0 100 200 30 0 400 500 600 700 800 Rnorm 1.01 0.99 0.97 4.7507 % 0 100 200 30 0 400 500 600 700 800 Lnorm 1.02 3. 016 % 1.01 1.00 0 100 200 30 0 400 Time (min) Fig 13 Measurands variations during 14 hours 500 600 700 800 98 Advances in Measurement Systems Here Lnorm is directly measured FP laser power (see Fig.11) normalized on its initial value Smallest variations . induced by Raleigh backscattering or any other way including imprinting of Bragg gratings inside the fiber. Taking into account the reflection from the ends of the sensing fiber, total power reflection. normalized transmitted power A D A+D Advances in Measurement Systems9 2 number of the intersecting lines. As we can see for very week losses nearly all lines cross the measurement- rectangular that means. superconducting bearings. Appl. Phys. Lett., 56(4): 39 7 -39 9 Okano M., T. Iwamoto, M. Furuse, S. Fuchino, I. Ishii, (2006). Runnin g performance of a pinning-type superconducting magnetic