International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017
p-ISSN: 2395-0072
www.irjet.net
FBG INTERROGATOR COMMUNICATION WITH THE EMBEDDED SYSTEM Akshaya D1, RK Karunavathi2 M.Tech Scholar Digital Electronics and Communication, Dept. of Electronics and Communication Engineering BIT, Bangalore, Karnataka, India 2 Associate Professor Dept. of Electronics and Communication Engineering BIT, Bangalore, Karnataka, India ---------------------------------------------------------------------***--------------------------------------------------------------------1
Abstract - FBG sensors are the optical sensors which are
stable SLED source and optical Fabry-Perot filter. In every interrogation system the interrogation monitor communicates the software which is designed to set the basic settings of the interrogator and to measure the FBG sensor results. In the process of making portable and flexible interrogator system, one idea is to replace the software application with that of the embedded system. This paper presents the method to replace software with that of the interrogator. For high resolution, high speed, and better SNR an interrogation method based on wavelength-swept lasers [8] is used.
sensitive to the external environmental conditions like temperature, pressure, strain. This feature of the FBG sensors make them suitable for many applications where electrical sensors are to be replaced due to their sensitivity to the electromagnetic interference and other radio frequency sources. FBG sensors are compact in size and their performance are not affected by the electrical sources. The sensed parameters of the FBG sensor should be analyzed using the interrogator monitor. To measure and test these external parameters the computer based application is used, which is connected to the interrogator. In all most every application where the FBG sensor is used to measure the external parameters, interrogator used a specific software which is installed in the PC. This paper aims to eliminate the use of software to measure and test the FBG sensor results. Instead it demonstrates the use of embedded system which communicates with the interrogator to perform measurement analysis.
2. BACKGROUND 2.1 Basic principle of the FBG sensor The fiber bragg grating sensors are optical sensors, formed by writing gratings inside the optical fiber. The refractive index changes periodically inside the core of the optical fiber when it is exposed to the UV radiations. In the interrogation system SLED is used as an optical source that illuminates the broadband light on the FBG sensor. The FBG sensor works with the principle of fiber bragg wave length. When a broadband light illuminates on the FBG sensor, it transmits all other wavelength except the one wavelength which is called bragg wavelength. It reflects the bargg wave length, and the shift in the bragg wave length takes place based on the external parameters like temperature, pressure and strain. The shift in the bragg wavelength gives the amount of external parameter that is experienced by the FBG sensor. The bragg wave length is given as :
Key Words: FBG; Interrogator; Embedded system; Temperature; Strain; Stress.
1.INTRODUCTION In some applications external parameters like temperature, pressure, strain should be monitored continuously for their better performance. Several low cost FBG interrogator systems were developed [1-3] to perform wavelength analysis of the FBG sensor. Compared to that of the electrical sensors, FBG sensors have higher sensitivity to the above mentioned parameters and are insensitive to electrical sources. This makes wide spread use of FBG sensors in many applications. FBG sensors can also be used to measure ultrasound, magnetic fields, acceleration and vibration [3]. Multiple FBG sensors are used in the aircrafts [4], civil structural monitoring, monitoring wind turbines [2], transformer monitoring. The sensed results of the FBG sensors are analysed using different interrogation techniques. In large scale applications FBG arrays can be used to measure different parameters [5]. Single optical fiber with multiple gratings results in a fiber bragg grating array. Spectroscopy based interrogator is the recent development for numerous microwave photonics applications [6]. Many different interrogators are used which is compatible with that of different FBG sensors. But the portable interrogation system will be of great benefit [7] which uses temperature
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Where , is the bragg wavelength, n is the refractive index, ĘŒ is the spacing between the gratings. The reflected wavelength is given to the interrogator that performs wavelength analysis. The 3 port optical circulator is used to connect between optical source, FBG sensor and the interrogator. The figure 1 shows the basic settings of the interrogation system. A spectrometer based interrogator is used in the interrogation system. An optical spectrometer is used to measure the light properties over a specific portion of the electromagnetic spectrum. The spectral lines are produced by the spectrometer. From the sensor through circulator, the spectrometer in the interrogator takes the reflected light. The spectral lines are imaged on the detector photons which are
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