1、 附件 外文翻译 Optic fiber-based dynamic pressure sensor for WIM system Shenfang Yuana, , , Fahard Ansarib, Xiaohui Liua and Yang Zhaob aThe Aeronautical Key Laboratory for Smart Materials and Structures, Nanjing University of Aeronautics and Astronautics, 29 YuDao Street, Nanjing 210016, China bDepartmen
2、t of Civil and Materials Engineering, University of Illinois at Chicago, Illinois, IL 60607, USA Received 16 August 2004； accepted 10 November 2004. Available online 15 December 2004. Abstract An optic fiber-based dynamic pressure sensor is described here to measure weight-in-motion of vehicles. In
3、the research reported herein, a Michelson interferometer with specially designed hardware and software were developed and experimentally subjected to dynamic compressive loads of different magnitudes, and loading rates. Experiments showed that both output fringe number and fringe period could be use
4、d to indicate the dynamic load. A calibration technique has been put forward to calibrate the sensor. Both the dynamic weight and static weight of the vehicle passed can be obtained. The findings that resulted from these studies developed an understanding for the behavior of interferometer sensor un
5、der dynamic compressive states of stress and are fundamental to the application of fiber optic sensors for the monitoring of truck vehicle weights while in motion. Keywords: Optic fiber sensor； Dynamic pressure； Weight-in-motion； Hardware and software Article Outline 1. Introduction 2. The sensor de
6、sign 2.1. Sensor setup 2.2. Sensor principle 3. Experimental procedures and results 3.1. Experimental setup 3.2. Experimental data 3.3. Repeatability of the sensor 3.4. Calibration of the sensor 3.4.1. Calibration of the static weight 3.4.2. Calibration of the dynamic weight 4. Conclusion References
7、 Vitae 1. Introduction The need to weigh vehicles in motion, applied especially to traffic control, has grown substantially in the past decades. Several techniques for weighting vehicles in-motion are now used including piezoelectric cables, capacitive mats, hydraulic and bending-plate load cells 1.
8、 Hydraulic and bending-plate load cells offer high accuracy (15%) and dynamic range, yet suffer from high installation costs and size constraints. The piezoelectric and capacitive mat techniques are substantially lower in cost, yet are less accurate (515%) and do not function properly at speeds lowe
9、r than 20 km/h 2 and 3. To offer the required accuracy at reduced installation and maintenance costs, optic fiber-based WIM sensors are now being developed to improve, complement or even replace the ones currently in use. Based on the effect of polarization coupling between two orthogonally polarize
10、d eigenmodes of polarization-maintaining fiber, Ansari et al. report on using highly birefringence polarization-maintaining (HiBi) fiber for dynamic measurement of pressure with practical ramifications to the determination of weigh-in-motion of trucks 3. Navarrete and Bernabeu report a multiple fibe
11、r-optic interferometer consisting of a Mach-Zehnder interferometer configuration with one of its arms replaced by another Mach-Zehnder interferometer 4. Cosentino and Grossman developed a dynamic sensor using the microbend theory to test weight-in-motion 5. The present work describes the development
12、 of a dynamic pressure sensor based on the Michelson interferometer, which has simple structure, is cost effective and can potentially offer the high accuracy required for many applications. Special hardware and system software based on Labview WINDOWS/CVI are designed to implement the sensor functi
13、ons, such as eliminating environmental noise, self-triggering of the test procedure and the fringe number and fringe period simultaneous count. Responses of the dynamic sensor are studied when subjected to dynamic compressive loads with different magnitudes and loading rates. Data calibration method
14、 is also researched to calibrate the sensor. 2. The sensor design 2.1. Sensor setup Fig. 1 illustrates schematically the proposed dynamic pressure sensor system. Single-mode optical fiber is used as a sensing element to form a Michelson interferometer. The optoelectronics components of the interfero
15、meter consist of a laser operating at wavelength of 1550 nm, a laser isolator and a photodiode. The sensor is made of communication grade optical fiber (Corning SMF28). The output signal from the detector-amplifier is first fed to a special hardware circuits including a two-order high pass filter, a
16、 zero-point detection circuit and a Schmitt Trigger circuit. The hardware circuits are designed to implement the following functions: (1) self-diagnose the arrival time of the vehicle to self-trigger the measurement process； (2) provide function to eliminate the low frequency disturbances, such as t
17、emperature influences and slow changes of the elements performances； (3) provide function to reduce the noise to a frequency band similar to the useful fringe output of the Michelson interferometer. One possible source of this noise is caused by vehicles passing in a near-by lane. Since the output o
18、f the Michelson interferometer under pressure is fringe which can be considered as high frequency signal comparing to the noise caused by temperature changes, laser and diode performance change and other low frequency environmental influences, a two-order high pass filter was adopted to eliminate th
19、ose low frequency components. A zero-point detection circuit is designed to change the sine-form fringe to pulse signal for the counter in the computer data acquisition system to count the fringe number and measure the fringe period. The self-trigger function is accomplished by the Schmitt circuit.
20、The threshold voltage of the Schmitt circuit is set according to experiments to distinguish the real fringe signal caused by vehicles and the pseudo fringe signal caused by small vibration in the test environment. In practical application, this could be caused by the passing vehicles in adjoining la
21、nes. System software based on Labview Windows/CVI is designed to set measurement parameters, control the test procedure and display results. Full-size image (14K) Fig. 1. Dynamic fiber optic pressure sensor setup. 2.2. Sensor principle One arm of the Michelson interferometer is subjected to a distri
22、buting dynamic load Ld(t). The generalized stressoptic relationship between the optical path change l and the strain induced over the gauge length can be derived as Eq. (1)6: (1) and (2) where P11 and P12 are the Pockels constant； l the length(gauge length) of the optical fiber within the pressure f
23、ield； tx, ty and tz correspond to the mechanical and geometrical property of the optical fiber and the host material-epoxy. By measuring the deformation of the fiber, the strain in the host material can be measured. The strain is linearly proportional to the external applied pressure p. Consider as a constant of proportionality between the pressure and the change in length of the fiber l, then (3) and (4) Thus, the output fringe number of the Michelson interferometer is (5)
