A new fiber-optic current sensor (FOCS) is described which employs phaseshifting algorithms to process the optical signal. In this approach the sensing element consists of a coil low birefringence fiber placed betwee...
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ISBN:
(纸本)9780819469304
A new fiber-optic current sensor (FOCS) is described which employs phaseshifting algorithms to process the optical signal. In this approach the sensing element consists of a coil low birefringence fiber placed between one polarizer and four analyzers. In the polarimeter layout, the output light from the current sensing element is divided into four beams through three nonpolarizing beamsplitters, and in each beam path is placed an analyzer and a detector. This paper discusses the characteristics of the optical current sensors, specifically for relaying applications were measurement of fault current is required. The design of the sensor, results and shiftalgorithms for electrical current characterization will be presented.
Based on the improved five-interferogram algorithm, a novel interferometer with special etalon is developed. The distance between two standard surfaces of this etalon can be changed by pressure in vertical direction t...
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Based on the improved five-interferogram algorithm, a novel interferometer with special etalon is developed. The distance between two standard surfaces of this etalon can be changed by pressure in vertical direction to realize phaseshift and can be come back with accuracy better than 0.1 nm when the pressure is free. The measurement standard uncertainty of diameter of the silicon sphere is better than 3 nm and measurement standard uncertainty of the silicon crystal density is 1 × 10-7.
In this paper, we studied on the detection of series arcing which is a main cause of electrical fires in low-voltage indoor wiring system. To distinguish series arcing state from normal one, we proposed a detection me...
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ISBN:
(纸本)9781424416219
In this paper, we studied on the detection of series arcing which is a main cause of electrical fires in low-voltage indoor wiring system. To distinguish series arcing state from normal one, we proposed a detection method based on that the magnitude of are voltage included in AC voltage varies at random during series arcing. We designed and fabricated a high-pass filter with the low cut-off frequency of 3kHz to attenuate AC voltage by -80dB or below, and to pass arc voltage without distortion. Also, a phase shift algorithm which eliminates the periodic component of arc voltage was used for nonlinear loads like incandescent lamps controlled by a dimmer.
A four-frame phaseshift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phaseshifter nonlinearity because of the perf...
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A four-frame phaseshift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phaseshifter nonlinearity because of the performance of a special procedure, in which the phaseshifts are shared out between the reference beam and the object beam. By this means, any phaseshifter can work as long as one phaseshift is accurately known. On the basis of the technique, a simple calibration method for the linear phaseshifter is suggested. The influences of phaseshifter miscalibration, detector nonlinearity and random noise on the algorithm are investigated, and the optimal phaseshifts are given.
White light interference is an extremely powerful method of optical measurements. When the structure of the interferometer, the spectrum width of the light source, and the scanning step is certain, the right algorithm...
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White light interference is an extremely powerful method of optical measurements. When the structure of the interferometer, the spectrum width of the light source, and the scanning step is certain, the right algorithm can achieve higher precision. The algorithms such as centroid algorithm, phase shift algorithm, envelope fitting algorithm and spatial frequency domain algorithm were discussed and compared. A complete reference was supplied for choosing of white light interferometry algorithm.
Wavelength tuning interferometry can distinguish interference signals from different surfaces in frequency space. The optical thickness variation of each layer of a multiple-surface object was measure
Wavelength tuning interferometry can distinguish interference signals from different surfaces in frequency space. The optical thickness variation of each layer of a multiple-surface object was measure
Wavelength scanned interferometry can distinguish in frequency space interference signals from different surfaces and therefore allows the measurement of optical thickness variation between several quasi-parallel surf...
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ISBN:
(纸本)0819454699
Wavelength scanned interferometry can distinguish in frequency space interference signals from different surfaces and therefore allows the measurement of optical thickness variation between several quasi-parallel surfaces of a composite transparent object. Discrete Fourier analysis of the signal spectrum with a suitable sampling window can then detect the phase of the individual signals. The actual frequencies of the various signals can deviate from their nominal detection frequencies because of refractive index dispersion of the material and/or nonlinearities in the wavelength scanning. This creates problems for conventional sampling window functions, such as the von Hann window, because they are sensitive to detuning of the signal frequency. Therefore we have derived an error-compensating algorithm (with 2N-1 samples and individual phase steps of 2pi/N) with a modified triangular window that allows some frequency detuning and can determine the phase of any specific harmonic order within the frequency range of the detected signal. A composite object consisting of four reflecting surfaces was measured using the new algorithm in a Fizeau interferometer. Experimental results show that the new algorithm measured the front surface and the optical thickness variations in a glass-air-glass cavity with an error of 10 nm rms over a 90 mm diameter aperture.
Wavelength scanning interferometry allows the simultaneous measurement of the surface profile and the optical thickness variation of a parallel plate. However, it is necessary to evaluate the modulation frequencies of...
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ISBN:
(纸本)0819445444
Wavelength scanning interferometry allows the simultaneous measurement of the surface profile and the optical thickness variation of a parallel plate. However, it is necessary to evaluate the modulation frequencies of the signal and noise which depend on the optical thickness and dispersion of the test plate. New nineteen-sample, wavelength scanning algorithms allow variation in these parameters and give a measurement resolution of 1-2 nanometers rms. Measurement of a BK7 near-parallel plate of 250 nun diameter and 25 mm thickness was demonstrated in a Fizeau interferometer.
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