Blade and Shaft Crack Detection Using Torsional Vibration Measurements Part 2: Resampling to Improve Effective Dynamic Range

2001 ◽  
Vol 32 (2) ◽  
pp. 23-26 ◽  
Author(s):  
Kenneth P. Maynard ◽  
Martin Trethewey
Keyword(s):  
Torsional Vibration ◽  
Crack Detection ◽  
Natural Frequencies ◽  
Dynamic Range ◽  
Detection System ◽  
Signal To Noise Ratio ◽  
Development Project ◽  
Experimental Apparatus ◽  
Effective Dynamic ◽  
Blade Crack

The primary goal of the development project was to demonstrate the feasibility of detecting changes in blade bending natural frequencies (such as those associated with a blade crack) on a turbine using non-contact, non-intrusive measurement methods. The approach was to set up a small experimental apparatus, develop a torsional vibration detection system, and maximize the dynamic range and the signal to noise ratio. The results of the testing and analysis clearly demonstrated the feasibility of using torsional vibration to detect the change in natural frequency of a blade due to a change in stiffness such as those associated with a blade crack. However, it was found that harmonics of shaft operating speed, created as an unwanted artifact of the measurement method, resulted in spectral regions in which the effective dynamic range was inadequate to detect low-level torsional vibration associated with the natural frequencies. The loss of effective dynamic range was due to the “skirts” created by the sampling window. Application of order resampling, followed by frequency resampling, to the torsional vibration waveform increased the effective dynamic range and improved the ability to identify shaft torsional and blade bending natural frequencies.

Constant-Fraction Discrimination/Boxcar Integrator for Plasma Source Time-of-Flight Mass Spectrometry

1995 ◽  
Vol 49 (5) ◽  
pp. 660-664 ◽  
Author(s):  
Pengyuan Yang ◽  
David P. Myers ◽  
Gangqiang Li ◽  
Gary M. Hieftje
Keyword(s):  
Mass Spectrometry ◽  
Inductively Coupled Plasma ◽  
Dynamic Range ◽  
Detection System ◽  
Signal To Noise Ratio ◽  
Time Of Flight ◽  
Plasma Source ◽  
Flight Mass Spectrometry ◽  
Lower Amplitude ◽  
Boxcar Integrator

A constant-fraction discrimination (CFD) system has been combined with a boxcar integrator for detection in inductively coupled plasma/time-of-flight mass spectrometry. The discriminator provides gating logic for the boxcar integrator when an incoming ion signal occurs, but discriminates against electronic or background noise of lower amplitude. As a result, the combination can effectively reject noise and accumulate analyte signal, rather than relying on an averaging process to reduce noise levels. The signal-to-noise ratio is therefore enhanced in this operation compared with the conventional boxcar method. The dynamic range of the detection system is at least five orders of magnitude.

Key elements of total seismic field design using Mathematica—A tutorial

Geophysics ◽  
2002 ◽  
Vol 67 (4) ◽  
pp. 1020-1027 ◽  
Author(s):  
Ninos Benyamin
Keyword(s):  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Computer Language ◽  
Signal To Noise ◽  
Seismic Surveys ◽  
System Noise ◽  
Effective Dynamic ◽  
Seismic Recording ◽  
Computer Based ◽  
Receiver Arrays

This tutorial reviews the basics of total seismic field design and provides personal‐computer–based computer language codes that can readily be used, with some modification, to design seismic surveys in the field. The finite effective dynamic range of seismic recording systems together with an overlap of signal and noise spectra suggest that a certain amount of prefiltering is needed during the acquisition phase to insure that a weak signal does not fall below the system noise, which would render the signal useless. The key elements of a total seismic field design are reviewed and, by way of a hypothetical 3‐D field example, their implementation is illustrated. The recommended solution consists of parameters for spread geometry that will record maximum geologic dips without aliasing, and shot and receiver arrays that optimize the signal‐to‐noise ratio.

An Over 120dB Dynamic Range Linear Response Single Exposure CMOS Image Sensor with Two-stage Lateral Overflow Integration Trench Capacitors

2020 ◽  
Vol 2020 (7) ◽  
pp. 143-1-143-6 ◽  
Author(s):  
Yasuyuki Fujihara ◽  
Maasa Murata ◽  
Shota Nakayama ◽  
Rihito Kuroda ◽  
Shigetoshi Sugawa
Keyword(s):  
Linear Response ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Cmos Image Sensor ◽  
Image Sensor ◽  
Signal To Noise ◽  
Single Exposure ◽  
Two Stage ◽  
Noise Ratio ◽  
Maximum Signal

This paper presents a prototype linear response single exposure CMOS image sensor with two-stage lateral overflow integration trench capacitors (LOFITreCs) exhibiting over 120dB dynamic range with 11.4Me- full well capacity (FWC) and maximum signal-to-noise ratio (SNR) of 70dB. The measured SNR at all switching points were over 35dB thanks to the proposed two-stage LOFITreCs.

scholarly journals Complex wavefront sensing based on coherent diffraction imaging using vortex modulation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rujia Li ◽  
Liangcai Cao
Keyword(s):  
Phase Retrieval ◽  
Dynamic Range ◽  
A Priori ◽  
Measured Intensity ◽  
Physical Constraints ◽  
Coherent Diffraction Imaging ◽  
Effective Dynamic ◽  
Ill Posed ◽  
Retrieval Problem ◽  
Diffraction Imaging

AbstractPhase retrieval seeks to reconstruct the phase from the measured intensity, which is an ill-posed problem. A phase retrieval problem can be solved with physical constraints by modulating the investigated complex wavefront. Orbital angular momentum has been recently employed as a type of reliable modulation. The topological charge l is robust during propagation when there is atmospheric turbulence. In this work, topological modulation is used to solve the phase retrieval problem. Topological modulation offers an effective dynamic range of intensity constraints for reconstruction. The maximum intensity value of the spectrum is reduced by a factor of 173 under topological modulation when l is 50. The phase is iteratively reconstructed without a priori knowledge. The stagnation problem during the iteration can be avoided using multiple topological modulations.

scholarly journals Detectivity optimization to detect of ultraweak light fluxes with an EM-CCD as binary photon counter array

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ibtissame Khaoua ◽  
Guillaume Graciani ◽  
Andrey Kim ◽  
François Amblard
Keyword(s):  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Photon Counting ◽  
Detection Methods ◽  
Strong Nonlinearity ◽  
Wide Range ◽  
Depth Analysis ◽  
Spatially Extended ◽  
Extended Sources ◽  
Photon Counting Mode

AbstractFor a wide range of purposes, one faces the challenge to detect light from extremely faint and spatially extended sources. In such cases, detector noises dominate over the photon noise of the source, and quantum detectors in photon counting mode are generally the best option. Here, we combine a statistical model with an in-depth analysis of detector noises and calibration experiments, and we show that visible light can be detected with an electron-multiplying charge-coupled devices (EM-CCD) with a signal-to-noise ratio (SNR) of 3 for fluxes less than $$30\,{\text{photon}}\,{\text{s}}^{ - 1} \,{\text{cm}}^{ - 2}$$ 30 photon s - 1 cm - 2 . For green photons, this corresponds to 12 aW $${\text{cm}}^{ - 2}$$ cm - 2 ≈ $$9{ } \times 10^{ - 11}$$ 9 × 10 - 11 lux, i.e. 15 orders of magnitude less than typical daylight. The strong nonlinearity of the SNR with the sampling time leads to a dynamic range of detection of 4 orders of magnitude. To detect possibly varying light fluxes, we operate in conditions of maximal detectivity $${\mathcal{D}}$$ D rather than maximal SNR. Given the quantum efficiency $$QE\left( \lambda \right)$$ Q E λ of the detector, we find $${ \mathcal{D}} = 0.015\,{\text{photon}}^{ - 1} \,{\text{s}}^{1/2} \,{\text{cm}}$$ D = 0.015 photon - 1 s 1 / 2 cm , and a non-negligible sensitivity to blackbody radiation for T > 50 °C. This work should help design highly sensitive luminescence detection methods and develop experiments to explore dynamic phenomena involving ultra-weak luminescence in biology, chemistry, and material sciences.

Blade Crack Detection using Blade Tip Timing

2021 ◽  
pp. 1-1
Author(s):  
Shuming Wu ◽  
Zengkun Wang ◽  
Haoqi Li ◽  
Zhibo Yang ◽  
Shaohua Tian ◽  
...  
Keyword(s):  
Crack Detection ◽  
Blade Tip ◽  
Blade Crack

scholarly journals Detection and localization of multiple small damages in beam

2021 ◽  
Vol 13 (1) ◽  
pp. 168781402098732
Author(s):  
Ayisha Nayyar ◽  
Ummul Baneen ◽  
Syed Abbas Zilqurnain Naqvi ◽  
Muhammad Ahsan
Keyword(s):  
Frequency Response ◽  
Natural Frequencies ◽  
Signal To Noise Ratio ◽  
Moving Average ◽  
A Priori ◽  
Damage Index ◽  
High Signal ◽  
Frequency Range ◽  
Spatial Locality ◽  
System Frequency

Localizing small damages often requires sensors be mounted in the proximity of damage to obtain high Signal-to-Noise Ratio in system frequency response to input excitation. The proximity requirement limits the applicability of existing schemes for low-severity damage detection as an estimate of damage location may not be known  a priori. In this work it is shown that spatial locality is not a fundamental impediment; multiple small damages can still be detected with high accuracy provided that the frequency range beyond the first five natural frequencies is utilized in the Frequency response functions (FRF) curvature method. The proposed method presented in this paper applies sensitivity analysis to systematically unearth frequency ranges capable of elevating damage index peak at correct damage locations. It is a baseline-free method that employs a smoothing polynomial to emulate reference curvatures for the undamaged structure. Numerical simulation of steel-beam shows that small multiple damages of severity as low as 5% can be reliably detected by including frequency range covering 5–10th natural frequencies. The efficacy of the scheme is also experimentally validated for the same beam. It is also found that a simple noise filtration scheme such as a Gaussian moving average filter can adequately remove false peaks from the damage index profile.

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