FFT Spectrum Analysis Research Articles

A low computation detection method of signal nonlinear distortion based on digital quadrature detection principle

This paper presents a digital low computation detection method for signal nonlinear distortion. After presetting ADC sampling rate and completing data sampling, the low sampling rate data extracted from the sampling data complete the autocorrelation analysis to correct and calculate the accurate fundamental frequency. According to the relationship between the fundamental frequency and the sampling rate, the complete periodic segment data of the signal cutting out from the sampling data carry out the digital quadrature detection operation to obtain the value of each harmonic component and nonlinear distortion. Experiments show that the calculation of this method is less than that of FFT spectrum analysis method when measuring the THD lower than 15 order. When calculating the 15-order THD at 1024 points, the calculation time is reduced by 44.26%. Moreover, the digital quadrature detection method has high measurement accuracy with less than 0.6% error of detecting 5-order THD.

Enhanced identification of bridge modal parameters using contact residuals from three-connected vehicles: Theoretical study

In this study, using two residual contact responses from three-connected moving vehicles is proposed to enhance the identification of bridge modal parameters. Based on the analytical formulation of the residual contact-point accelerations, the contact-point accelerations are back-calculated from the vertical accelerations of three vehicles, from which the magnitudes of pavement irregularity-related frequencies can be largely reduced in the two residual contact responses. From the residual contact responses, the bridge frequencies are identified by conducting FFT spectrum analysis, while the damping ratios are estimated using curve fitting of the free-decay components extracted by random decrement technique and variational mode decomposition. Unlike the incomplete construction of the mode shapes of a bridge using one residual response from two-connected vehicles, the proposed method can retrieve the complete mode shapes of a bridge. Since the two contact residual accelerations can be expressed as the interpolation of bridge mode shapes, the latter can be retrieved by performing the singular value decomposition of the residual response matrix. To recover the invalid measured data in retrieving the bridge mode shapes, the singular value thresholding algorithm is applied. The effectiveness and robustness of the method are validated by the numerical examples considering a wide range of practical conditions, particularly, with the merit of application to various boundary conditions of bridges in comparison with the commonly adopted technique.

Calibration of an RF/Microwave Phase Noise Meter with a Photonic Delay Line

The main advantage of phase noise meters with photonic (fiber) delay lines is that they do not require high-performance, low-noise reference oscillators. On the other hand, some additional calibrations are required, which are the subject of this paper. First, the quadrature must be maintained on the mixer by precise adjustment of the phase and/or delay. Next, since the response of the mixer is proportional to the square of the input test signal, a precise amplitude calibration is required. Finally, the frequency response of the FFT spectrum analyzer and its corresponding anti-aliasing low-pass filter needs to be known precisely. In this paper, to the best of our knowledge, we present innovative solutions for all three calibrations. All three calibrations were built in and tested in our phase noise meter. The result is a simple and robust phase noise meter suitable for non-laboratory environments.

MATLAB SIMULATION RESEARCH ON PERMANENT MAGNET SYNCHRONOUS MOTOR VECTOR CONTROL

According to the mathematical model of PMSM (permanent magnet synchronous motor) and vector control method, PMSM FOC (vector control) simulation model is built on the basis of MATLAB/Simulink environment. The system adopts the rotor field oriented vector control method of id 0 to realize PMSM decoupling control. The speed regulator and current regulator uses the conventional PI control algorithm, and the inverter adopts SVPWM modulation strategies. The simulation results proved the feasibility of the control method, which provides a good theoretical basis for the parameters of PMSM control system hardware settings. At the same time, building simulation model PMSM FOC SPWM modulation strategy on the basis of FOC SPVWM simulation, making FFT (spectrum analysis) comparison between which and the SVPWM modulation's single phase current. The result that the output harmonic of SVPWM modulation is far less than SPWM modulation proves the advantages of SVPWM modulation strategies. 

Determining the dynamic characteristics of an existing timber belfry structure and impact on FEM modelling

The paper studies the assessment of the dynamic characteristics of an existing historic timber belfry structure using FEM modelling and dynamic identification tests performed on a structure. The analysed structure undergoes geometrically measurement, including elements inspection, and on this basis the corresponding initial FEM model was built. The initial model including actual dead loads was computed to achieve dynamical and static calculations results, including eigenmodes and modal masses. On the belfry structure, dynamic identification tests were performed using accelerometers arranged in places of expected maximum amplitudes for belfry parts. The same initial model was calibrated according to the data achieved from computing in-situ identification tests (FFT spectrum analysis) and recalculated for static and dynamic results. Computed results from the initial and calibrated models were compared, presented and discussed. Brief summary includes conclusions from analysis and contribution to researches on belfries dynamics.

A high performance fast-Fourier-transform spectrum analyzer for measuring spin noise spectrums**Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDC0702200), the National Key R&D Program of China (Grant Nos. 2018YFA0306600 and 2016YFB0501603), the National Natural Science Foundation of China (Grant No. 11927811), the Chinese Academy of Sciences (Grants Nos. GJJSTD20170001 and QYZDY-SSW-SLH004), Anhui

A high performance fast-Fourier-transform (FFT) spectrum analyzer, which is developed for measure spin noise spectrums, is presented in this paper. The analyzer is implemented with a field-programmable-gate-arrays (FPGA) chip for data and command management. An analog-to-digital-convertor chip is integrated for analog signal acquisition. In order to meet the various requirements of measuring different types of spin noise spectrums, multiple operating modes are designed and realized using the reprogrammable FPGA logic resources. The FFT function is fully managed by the programmable resource inside the FPGA chip. A 1 GSa/s sampling rate and a 100 percent data coverage ratio with non-dead-time are obtained. 30534 FFT spectrums can be acquired per second, and the spectrums can be on-board accumulated and averaged. Digital filters, multi-stage reconfigurable data reconstruction modules, and frequency down conversion modules are also implemented in the FPGA to provide flexible real-time data processing capacity, thus the noise floor and signals aliasing can be suppressed effectively. An efficiency comparison between the FPGA-based FFT spectrum analyzer and the software-based FFT is demonstrated, and the high performance FFT spectrum analyzer has a significant advantage in obtaining high resolution spin noise spectrums with enhanced efficiency.

Dynamic analysis of Compressor Mounting Bracket in Automobiles

The experimental modal analysis has developed very fast since the start of digital FFT spectrum analyzer in the early 1970s. Nowadays, impact testing (or bump testing) has become well-known as quick and economical option to find the modes of vibration of a machine or structure. This paper presents the comparison of the experimental and numerical modal analysis of a compressor mounting bracket (CMB) made of Aluminum and mild steel. The dynamic behavior of CMB is investigated by performing the model analysis in Ansys-15 software. The 3-D finite element models are constructed using Altair Hyper Mesh and a numerical modal analysis is then performed to generate mode shapes and natural frequencies in three-orthogonal directions. The both finite element model agrees well with the simulation tests and eventually helps the designer to act upfront with much lesser cost and experimentation time.

A Novel Self-Calibration Method for Acoustic Vector Sensor

The acoustic vector sensor (AVS) can measure the acoustic pressure field’s spatial gradient, so it has directionality. But its channels may have nonideal gain/phase responses, which will severely degrade its performance in finding source direction. To solve this problem, in this study, a self-calibration algorithm based on all-phase FFT spectrum analysis is proposed. This method is “self-calibrated” because prior knowledge of the training signal’s arrival angle is not required. By measuring signals from different directions, the initial phase can be achieved by taking the all-phase FFT transform to each channel. We use the amplitude of the main spectrum peak of every channel in different direction to formulate an equation; the amplitude gain estimates can be achieved by solving this equation. In order to get better estimation accuracy, bearing difference of different training signals should be larger than a threshold, which is related to SNR. Finally, the reference signal’s direction of arrival can be estimated. This method is easy to implement and has advantage in accuracy and antinoise. The efficacy of this proposed scheme is verified with simulation results.

Effect of lubrication on machining response and dynamic instability in high-speed micromilling of Ti-6Al-4V

The micromilling process is increasingly being used in biomedical, defence, electronics and aerospace industries for fabrication of miniaturized products of complex shapes. For difficult-to-cut materials like Ti alloys, limited stiffness of the micro-tool is a major impediment. This limitation can be overcome by using high rotational speeds which leads to reduction in chip load and, therefore, the cutting forces. However, high spindle speeds and low tool stiffness can render the process unstable due to dynamic variation in cutting forces. High speed micromilling of Ti6Al4V generates high temperature in cutting zone due to low thermal conductivity of Ti alloys which can also lead to a variation in cutting force and, hence, dynamic instability. Cutting fluid can play an important role because of its capacity to reduce friction and its ability to dissipate the heat generated between the micro tools and the workpiece. This study is focused on studying the effect of lubrication on the cutting forces and dynamic instability called chatter in high speed micromilling of Ti6Al4V. Experiments were carried out at different spindle speeds and feeds in both dry and lubricated condition. A significant reduction up to 38% in the cutting forces has been found in lubricated machining as compared with the dry machining. Two distinct regimes, lubrication sensitive (at rotational speeds >47,000rpm) and lubrication insensitive (at rotational speeds <47,000rpm) have been observed in this study. A critical spindle speed of 47,000rpm has been identified which corresponds to the onset of lubrication dominant regime. To capture the effect of process mechanics, mechanistic force model using velocity-chip load dependent coefficients has been used to predict the forces and stability boundary. The predicted stability boundary limits have been compared with the experimental onset of chatter at four different spindle speeds. FFT spectrum analysis of acceleration of workpiece has been done to detect the process instability.

Decrease selected graphomotor skills in early stages of Alzheimer's dementia

IntroductionIn the early stages of Alzheimer's disease (AD) motor and cognitive dysfunctions has been observed.ObjectivesIn previous studies we have shown that AD patients present abnormalities of selected graphomotor skills, but results were vary and not conclusive. In this study, we conducted more extensive tests on a larger study group.AimsThe aim of the study is to identify which graphomotor functions are impaired in the early stages of AD.MethodsSeventy-one patients with mild and moderate AD (F.00.0, F.00.1, F.00.2) (MMSE 20.3 ± 3.8; age 79.1 ± 5.21) were examined. Forty-four healthy ones (C) without symptoms of dementia, matched for demographic characteristics (MMSE 29 ± 1.1; age 78.3 ± 4.7) were examined. Graphomotor skills were assessed by the original drawing test (the eight figures and the signature) performed in a magnetic field (resolution 2540 dpi and 1024 pressure levels). These test were implemented on a graphic tablet (Wacom Intuos) with the specialized software. The length and time of drawing, the average and maximum speed of drawing, the average and maximum momentary speed, the amplitude and frequency (with FFT spectrum analysis) of hand tremors were measured.ResultsStatistical analysis of the graphomotor signal revealed differences between the AD group and the C group with respect to various parameters. The largest differences have been observed in partially automated skills such as signature, and not drawing shapes (lines, spiral, etc.). The average speed of signature and maximum momentary speed of signature is lower in the AD group.ConclusionsThis method allows for quantitative and objective measurement of the biophysical signal and assessment of the graphomotor skills.Disclosure of interestThe authors have not supplied their declaration of competing interest.

VIBRATION ANALYSIS OF CI ENGINE USING FFT ANALYZER

In automobile industry, the vibrations generated in the IC engine affects the performance of the vehicle and quality of comfort while riding the vehicle. The factors which are affected under continuous vibration of IC engine are drivability, stability and comfort. All these factors are reducing while there is an increase in vibrations produced by the engine. Reciprocating as well as rotating parts of the engine are producing vibrations continuously in the internal combustion engine. The inertial forces are produced by these reciprocating and rotating parts. These inertial forces are changing with compression and combustion characteristics inside the engine. The vibrations produced by the engine can be minimized by reducing those unbalanced forces generated during its functioning, otherwise anti vibration mounts are placed in between engine and its base. Many researchers have performed experimentations to see reasons behind the vibration generations also to reduce vibrations at interface between engine and its base. In this paper a thorough collection of data related to engine vibrations is made to provide a platform for future work. It encompasses various work carried on engine rigid body modeling. The paper is framed as engine rigid body modeling, engine vibrations in detail and at last some experimental work performed on a single cylinder diesel engine to measure vibrations using FFT spectrum analyzer.

An expert system for acoustic diagnosis of power circuit breakers and on-load tap changers

Most of the faults on power Circuit Breakers (CBs) and On-Load Tap Changers (OLTCs) on high voltage transformers are of mechanical origin. Mechanical malfunction, mechanical wear and other types of abnormal behaviors can be detected as changes in the acoustic signatures. In this paper, an Expert System (ES) with the addition of a signal processor module and factual database module to the conventional ES has been proposed for the diagnosis of CBs and OLTCs. The feature extraction of the acoustic signatures has been done by decomposing them into voiced and silent portions in time domain and through FFT spectrum analysis in frequency domain. The OLTC's motor current has been decomposed into inrush, steady-state and extended currents to locate the cause of different anomalies in the OLTCs and acoustic-current pair has been used for the synchronization testing. Each extracted feature of the testing signal has been compared to the similar feature of a reference signal to not only identify the health of the testing device but also to locate the cause of each anomaly. Several test signals have been compared against the reference signature and the proposed expert system has proved to be a suitable, effective and reliable system for the acoustic diagnosis of OLTCs and CBs.

Vibration Analysis of Multi Stages Rotor for Blade Faults Diagnosis

Blade fault is one of the most common faults in turbomachinery. In this article, a rotor system consists of multiple rows of blade was developed. The effectiveness of conventional FFT spectrum and wavelet analysis in the diagnosis of multi stage blade rubbing faults is examined at different stages, variety of blade fault conditions, and different blades rubbing severity. Blade fault caused impacts and the use of wavelets as analysis tool to detect the blade faults was studied. Results showed that, vibration spectrum can clearly depict the location and the stage of blade rubbing, while it is difficult to be identified in wavelet analysis. The limitations of wavelet analysis for multi stage blade fault diagnosis were identified. Some probable solutions to improve wavelet time-frequency representation in blade fault diagnosis were also presented.

Simulation and Analysis for Current Transformers with DC Bias and Remnant Flux

The transfer characteristics of current transformers (CT) change due to DC bias, which directly impacts the accuracy of measurement and power metering. Based on equivalent circuit models and core magnetizing characteristic, qualitatively analysis current transformer saturation increase errors of CT. Transfer errors under DC bias and remnant flux are also obtained based on J-A model of CT in PSCAD/EMTDC and full-wave Fourier algorithm to show that the ratio error and phase displacement increase with the DC bias. Based on FFT spectrum analysis to identify remnant flux and DC bias provides scientific basis for error compensation of CT.

Parameter Estimation of Low-Frequency Signal with Negative Frequency Contribution

According to the problem that there is a decline in accuracy of low-frequency signal parameter estimation by using the algorithm of all-phase FFT, an improved phase difference correcting spectrum method based on all-phase FFT is proposed. The contribution of negative frequency to FFT calculation was considered while using phase difference correcting spectrum method. The all-phase FFT spectrum analysis theory was presented as well as a traditional phase difference correcting method based on it. The equations of parameter estimation such as frequency, amplitude and phase for low-frequency signals were derived with the negative frequency contribution to spectrum analysis. The simulation results show that the method proposed in this paper can be used to estimate the parameters of low-frequency signals in a high accuracy, and also achieves an improvement in anti-noise ability.

Classification of sleep apnea using wavelet-based spectral analysis of heart rate variability

Obstructive Sleep Apnea (OSA) is the cessation of breathing during sleep due to the collapse of upper airway. Polysomnographic recording is a conventional method for detection of OSA. Although it provides reliable results, it is expensive and cumbersome. Thus, an advanced non-invasive signal processing based technique is needed. The main purpose of this work is to predict the severity of sleep apnea using an efficient wavelet-based spectral analysis method of the heart rate variability (HRV) to classify sleep apnea into three different levels (mild, moderate, and severe) according to its severity and to distinguish them from normal subjects. The standard FFT spectrum analysis method and the soft-decision wavelet-based technique are to be used in this work in order to rank patients to full polysomnography. Data of 20 normal subjects and 20 patients with mild apnea and 20 patients with moderate apnea and 20 patients of severe apnea are used in this study. The data is obtained from the sleep laboratory of Sultan Qaboos University hospital in Oman. Four different classification versions have been used in this work. Accuracy result of 90% was obtained between severe and normal subjects and 85% between mild and normal and 75% between severe and moderate and 83.75% between normal and patients. The VLF/LF power spectral ratio of the wavelet-based soft-decision analysis of the RRI data after a high-pass filter resulted in the best accuracy of classification in all versions.

Calculation of Lumped Parameter of Two-Port Network for Volume Conduction Energy Delivery

Skin electrode unit is the channel through which energy can be transferred to the implanted device by volume conduction. The unit can be equivalent to lumped circuit, but so far there are no appropriate calculation methods of these circuit parameters. In this paper, the field- circuit coupling model of skin electrode unit is established to compute the voltages and currents at electrode ports, then their amplitudes and phases are extracted by using all phase FFT spectrum analysis, at last the equivalent impedance parameters of the skin electrode unit are calculated by the application of variable load method. These impedance parameters can be used for optimizing the volume conduction energy delivery system.

Research on Wideband Guiding System Receiving Technology

The ultra-high speed data acquisition system is introduced, which has sampling rate of 3GSPS. The design scheme of hardware circuit is given in condition to analyze the theory and technology of signal sampling. The design of the main part circuit is described. The module of serial -parallel conversion and FFT spectrum analysis are designed in software realization. The system has strong commonality because of application of the ADC + FPGA + DSP framework.

A High Precise Automatic Test Platform for the Boards of Wind Power Converter

As the core component of wind turbine generator system, the quality of wind power converter attracts great attention. Traditionally, manual testing has been the way to ensure the board performance. Based on virtual instrument, a hardware-in-the-loop test platform is designed using the LabVIEW graphical programming language. A method based on FFT spectrum analysis shows high precision in detection the phase shift of current signals, which would outperform the zero-crossing method when noises could not be omitted; and a method based on BP neural network improves the calibration precision of temperature detection channels. The satisfying precision and efficiency in application show great advantage in many aspects compared to the traditional testing method.

On-Line Monitoring and Fault Diagnosis System of Fan Based on LABVIEW

This paper introduces an on-line monitoring and fault diagnosis system of Fan based on LABVIEW and Advantech PCI-1711 data acquisition card. Through the FFT spectrum analysis of domain vibration, four conditions corresponding to imbalance, misalignment, friction and oil whirl are tested. The result shows that the system can identify these common faults correctly. The system has the advantages of reliable stability, high accuracy and easy manipulation.