外文翻譯---使用雙光纖布拉格光柵傳感器和互相關(guān)技術(shù)的水流量計 英文

1、Sensors and Actuators A 116 (2004) 66–74A water flowmeter using dual fiber Bragg grating sensors and cross-correlation techniqueShoichi Takashima?, Hiroshi Asanuma, Hiroaki NiitsumaGraduate School of Environmental Studie

2、s, Tohoku University, 20 Aza Aoba, Aramaki, Aoba-ku, Sendai, JapanReceived 14 December 2003; received in revised form 11 March 2004; accepted 21 March 2004 Available online 27 July 2004AbstractIn this paper, a principle

3、and experimental results of a cross-correlation flowmeter using fiber Bragg grating (FBG) sensors are presented. The flowmeter has no electronics and no mechanical parts in its sensing part and the structure is thus simp

4、le and immune to electromagnetic interference (EMI). For water flow measurement, the flowmeter uses the time delay of the vortex signal generated by a bluff body. Karman vortex shedding frequency is also detected and uti

5、lized for the flow velocity estimation in the system. In order to realize a low noise and wide bandwidth system, we employed interferometric detection as a FBG wavelength-shift detection method. The noise spectral densit

6、y of the FBG sensor with the interferometric detection was 4 × 10?4 pm/(Hz)1/2 corresponding to 0.33 nε/(Hz)1/2. A water flow experiment showed that the flowmeter had a linear characteristic at velocity range from 0

7、 to 1.0 m/s and the minimum detectable velocity of 0.05 m/s. © 2004 Elsevier B.V. All rights reserved.Keywords: Fiber Bragg grating (FBG); Interferometric detection; Cross-correlation flowmeter; Karman vortex1. Intr

8、oductionFiber Bragg grating (FBG) sensors have various advan- tages such as small size, simplicity in sensing principle, elec- tromagnetic interference (EMI) immunity and capability of multiplexing. Because of these adva

9、ntages, a number of ba- sic researches and applications on FBG sensors have been made [1–3]. In telecommunication systems, FBGs are used as add-drop multiplexers because of their narrow bandwidth (typically 0.1 nm). The

10、FBG application to optical tunable filters is also useful for discrimination of the signals in FBG sensor systems [4]. The applications to smart structures and health monitoring are attractive and have been investigated

11、actively [5,6]. FBGs are embedded in composite materials and used as strain and temperature sensors in the applica- tion. In the field of civil engineering, strain measurements for bridges and buildings are made using FB

12、G sensor arrays with wavelength division multiplexing (WDM) and time di- vision multiplexing (TDM) [7]. In the FBG sensor applications, the choice of the wavelength-shift detection method is very important be- cause the

13、noise level and the measurement bandwidth of? Corresponding author. Tel.: +81-22-2177401; fax: +81-22-2177401. E-mail address: shoichi@ni2.kankyo.tohoku.ac.jp (S. Takashima).the system are mainly determined by the detect

14、ion method. The most commonly used detection method is the tunable filter detection using Fabry–Perot filter. This method is the standard technique and provides static or quasi-static mea- surement with a strain resoluti

15、on of 1 ?ε. Another promising method is the interferometric detection [8,9]. This method has the capability of dynamic measurement with high strain resolution in the order of nε/(Hz)1/2. There are some re- ports about th

16、e noise estimation of the FBG sensor with interferometric detection [10–12]. Our subject of research is the FBG application to a water flowmeter. There are various kinds of flowmeters including turbine flowmeters, vortex

17、 flowmeters and differential pres- sure type flowmeters. Measurands of flowmeters are ranging over various flow including water flow, gas flow and mul- tiphase flow. Cross-correlation flowmeter, which utilizes a time del

18、ay of signals by coherent structures including vortices and naturally existing unsteady pressure field, is usually used for pipe flow measurement. The advantage of the cross-correlation flowmeter is its simplicity in sen

19、sing principle. The only parameter required to the flowmeter is the distance between two sensors. In the cross-correlation flowmeter, two pair of a ultrasonic transmitter and a re- ceiver are usually used because of thei

20、r non-intrusiveness to the flow [13]. The flowmeter using the ultrasonic trans- ducers has a good linearity at wide velocity range. The0924-4247/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.

21、1016/j.sna.2004.03.02668 S. Takashima et al. / Sensors and Actuators A 116 (2004) 66–74Fig. 2. Schematic diagram of the flow measurement system.where p12 is the elasto-optic constant of the optical fiber and is approxima

22、tely 0.22. This yields the strain sensitivity of 1.2 pm/?ε. To obtain the shift δλB, the outputs of the interferometer are used, and the outputs Vm (m = 1, 2, 3) are expressed as follows [9]:Vm = αmVin + Re[Γ(τ)] = αmVin

23、[1 + γ cos(θMZI + θm)],(5)where Γ (τ) is the auto-correlation function of light wave reflected by the FBG sensor, Vin is the voltage corresponding to optical power reflected by the FBG sensor, and αm is the coefficient c

24、ompensating differences of photodetector sensitivities and obtained from preliminary experiments. If the split ratios of the 2 × 2 and 3 × 3 couplers are 1:1 and 1:1:1, respectively, one can obtain θ1 = 0, θ2 =

25、 2π/3 and θ3 = ?2π/3, and the outputs V1, V2 and V3 are derived as follows: ? ? ? ? ? ? ?? ? ? ? ? ?V1 = α1Vin(1 + γ cos θMZI)V2 = α2Vin?1 + γ cos?θMZI + 2π3??V3 = α3Vin?1 + γ cos?θMZI ? 2π3?? (6)The signal θMZI can be t

26、hen calculated using the following equation:θMZI = 2πLλB = tan?1 √3(V2 ? V3)V2 + V3 ? 2V1 , (7)where L is the optical path difference of the interferometer. The relationship between the signal variation δθMZI and the shi

27、ft δλB is expressed as follows:δθMZI = 2πLλB + δλB ? 2πLλB= ? 2πLλB(λB + δλB)δλB ≈ ?2πLλ2 B δλB, (8)where the term (λB + δλB) was assumed to be nearly equal to λB because the shift δλB is significantly smaller than λB. A

28、n accidental loss of optical power while measure- ment, which causes problems in optical intensity modula- tion type sensors, is admissible in some measure because the wavelength-to-phase sensitivity (=?2πL/λ2 B) depends

29、 on only the path difference L.3. Noise estimation of the FBG sensor with interferometric detectionThere are some reports about the noise estimation of FBG sensors with interferometric detection. However the noise estima

30、tion reports about the interferometric detection using a 2 × 2 and a 3 × 3 couplers have not been presented.3.1. Noise of the photodetectorFig. 3 shows the circuit diagram of the photodetector. The noise of the

31、 photodetector is defined by the noise of a photodiode and a transimpedance amplifier. The noise of the photodetector is determined by thermal noises due to the feedback resistance Rf of the transimpedance amplifier Rf a