Papers by Keyword: Waveform

Abstract: It is clear that lightning strokes produce overvoltages on Transmission Lines (TLs), which can be higher that the Basic Insulator Level (BIL), generating a fault or short circuit. Thus, in order to adequately analyze when a lightning hits on a TL, it is necessary to simulate different elements corresponding to Electric Power Systems (EPSs) as real as possible. In this context, transmission towers are considered crucial parameters in lightning studies, which must be correctly selected and simulated in order to consider reflected voltage waveforms from cross arms. Based on the above said, this paper presents a comparative study corresponding to the transmission tower simulation using two models. The first uses inductances, and the second uses distributed parameters impedances characterized by their impedance and travel time. This paper presents voltage variations that exist in each phase, using different lightning features. Alternative Transients Program (ATP) is used to simulate the TL model considering different lightning currents and the two tower models. Results show that the impedance model analyze reflected waveforms, while that the inductance model does not analyze this issue.

Abstract: With good repeatability and simple structure, transmission line pulse (TLP) has been used in immunity test of integrated circuit and printed circuit board. A TLP generator is first manufactured and its output waveform is presented. By using wavelet transform, the waveform is denoised and discriminated to components inherent to system function and parasitic parameters. Frequency spectrum changed with time is also obtained by continuous wavelet transform of complex morlet. Decomposed damping oscillation component and high frequency component in instant frequency spectrum show influence of inductance in circuit on the waveform. Improvement of rising time and overshoot is achieved by change of probe connection with shorter grounding line.

Abstract: Based on the SSRT, by simulating different forms of applied loads, the paper conducts the research on the influence and mechanism of action from different waveforms upon the stress corrosion of pipeline steel. Results show that under the given F - SSRT testing condition, and when the fluctuation frequency and fluctuation amplitude are same, the sensitivity of the stress corrosion produced upon X70 pipeline steel is the weakest under the F-SSRT testing condition of superimposed square wave, and is the strongest under the F-SSRT testing condition of superimposed sine wave, which shows that the sensitivity degree of stress corrosion of materials under the F-SSRT with different load waveforms is obviously different.

Abstract: The phenomenon of lubricant cavitation in hydrodynamic bearings and its detrimental effects have been documented in many literatures. Collapse of vapor cavitation bubbles may cause erosion wear that limits the life of the bearings. The ability to detect the occurrence of vapor cavitation using a well established condition monitoring technique is essential for the equipment operator. An experiment was conducted to investigate the vibration characteristics of vapor cavitation in steadily loaded plain journal bearings. Vibration data were collected from the bearings operating under the influence of vapor cavitation. It is shown that, vapor cavitation exhibits distinct characteristics on the vibration plots. Low amplitude, forward and reverse 0.063X frequency components, and a series of harmonics with frequencies lower than 0.5X, are observed on the full spectrum. A unique waveform with the positive peak amplitude fluctuating above and below the zero axis line is also observed.

Abstract: The processes involved in corrosion fatigue in general are briefly outlined, followed by a brief review of recent studies on the effects of cycle frequency (rise times) and electrode potential on crack-growth rates at intermediate ΔK levels for cathodically protected high-strength steels. New studies concerning the effects of fall times and hold times at maximum and minimum loads on crack-growth rates (for K_max values below the sustained-load SCC threshold) are presented and discussed. Fractographic observations and the data indicate that corrosion-fatigue crack-growth rates in aqueous environments depend on the concentration of hydrogen adsorbed at crack tips and at tips of nanovoids ahead of cracks. Potential-dependent electrochemical reaction rates, crack-tip strain rates, and hydrogen transport to nanovoids are therefore critical parameters. The observations are best explained by an adsorption-induced dislocation-emission (AIDE) mechanism of hydrogen embrittlement.

Abstract: In this paper, the hysteresis loop of Au/PZT/Pt/Al₂O₃/SiO₂/Si thin films was experimentally measured in different conditions as a waveform and a DC offset, using a precision LC Radiant technology RT-66. The measurements were taken by applying a drive to the Pt bottom electrode connected to the drive of the precision LC and the Au top electrode was connected to the drive of the precision LC. The waveform was applied as wave type = sine; peak voltage = 6 V; frequency = 1 KHz and duration = 100 s. The results show that, by applying waveform and DC offset the hysteresis loop softly changes the polarization (Pr) and coercive field (Vc).

Abstract: This paper studies the fast On-Load Tap Changer (OLTC) technology of contactless switch without transition resistance or transition reactor. It not only provides the equivalent circuit of OLTC, the impact current calculation formula and the OLTC simulation waveform based on the inductive load but also supplies with the main electrical circuit and the waveform recorded in the experiments. The MJN3 contactless voltage-controlled power source has been developed with MCT801D intelligent module, which can accomplish to rapidly switch in voltage-controlled gears based on the inductive load. Its output current is continuous with no impact, no over-voltage and voltage-drop, which can achieve the high performance and high reliability.

Abstract: For frequency modulate continuous wave radar, it is necessary and difficult to search the pairs of beat frequencies in an up-chirp mode and a down-chirp mode t o measure range and velocity of multiple targets. However, the inherent problem of FMCW radar is multiple targets detection. False targets can appearance because of mistaking the combination of these beat frequencies. A novel waveform named double-slope symmetrical saw-tooth wave is proposed and its corresponding algorithm is also introduced to resolve the problem of multiple targets detection for automotive anti-collision radar. Computer simulation results and theoretical analysis prove that the method is effective and practical for multiple targets detection in intelligence transportation system.

Abstract: Autocorrelation function and cross-correlation function can be used to illustrate the dependency relation of random processes. The degree of mini-transmutation is often too small to detect. A new approach via utilization of correlation coefficient between two different signals in time domain was proposed to measure the tiny distortion of three dimensional objects. The correlation analysis and deduction on transformation from 3-D surface distribution to 1-D time series signal were made rationally. Numeric simulation experiments of discrete digital signal generated from triangular function composite generator were done and six groups of correlation coefficient curves were given deliberately with different signal length. The correlation and similarity degree among different similar waveforms were analyzed in detail. It shows that the approach is valid to detect the degree of distortion between the original standard one and the practical one.

Abstract: Online fault non-destructive detection is crucial to the fabrication of high quality products of welds. In this study, a novel method in the field of weld whose name is Mahalanobis Distance Measurement (MDM) is illustrated and employed to determine whether welding faults have occurred or not. This method is based on an arc method which is employed to get the information of welding voltage and welding current. Through analyzing the calculation results of Mahalanobis Distance of the welding voltage and current signals, the important information of welding process has been obtained. At the meanwhile, whether a fault has occurred or not is decided. In order to verify the effect of the performance of the different width of the gap on the results of Mahalanobis Distance, two widths of the gap generated artificially were chosen: one is 2 mm and the other is 3 mm. The results of the experiment have demonstrated that using the thinking of Mahalanobis Distance to measure the weld faults is feasible.