1,721,204 research outputs found
Evaluation of the sensitivity to mechanical vibrations of an IR Fourier spectrometer
No full textThis article presents an experimental and theoretical investigation of the sensitivity to mechanical disturbances of a Fourier-transform infrared spectrometer, the Planetary Fourier Spectrometer, currently orbiting around Mars onboard ESA Mars Express orbiter. A theoretical analysis has been performed in order to highlight the expected effects of the vibrations, then laboratory tests have been designed and carried out for instrument characterization. The two classical types of disturbance effects were expected in the case of mechanical vibrations: the interfering type, leading to an additive contribution to the interferograms, and the modifying type, which changes the interferometer sensitivity. Both effects have been evidenced in the experimental tests and the instrument sensitivity derived; moreover, the effects on the spectra, which are the Fourier transform of interferograms, are highlighted and characterized. The effects of both harmonic and random broadband spectrum disturbances have been considered. While the broadband disturbances increase uniformly the noise, harmonic disturbances produce localized effects in the spectra and replicas of the spectral features with wave-number shifts proportional to disturbance frequency. It has also been highlighted that, the disturbances from mechanical vibrations being uncorrelated with the interferometric signals, by spectrum averaging, like all the other noise sources, they can be reduced. Methods for spectrum diagnostics and for increasing the signal-to-noise ratio in vibration-affected spectra are proposed as well. © 2005 American Institute of Physics
Analysis of disturbances in the Planetary Fourier Spectrometer through numerical modeling
No full textFourier transform spectrometers are instruments with high sensitivity to many kinds of disturbances. This study started from the analysis of the disturbances related to mechanical vibrations on the PFS FTIR spectrometer to show how the measured spectra can differ from the actual ones. The complete study, more in general, accounts for the characteristics of a real instrument and its operating environment to show, which can be the effects of many sources of disturbances on realistic measurements. The analysis is especially relevant when the spectra are used for the determination of parameters through "best fitting techniques" by matching with synthetic ones because it shows how spectral features used in these studies can be modified by disturbances. A previous work addressed the theoretical treatment of vibrations borne effects on FTIR spectrometers and is the ground work for the present; however, that study, being based on an analytical approach could only show examples of single effects on simplified input signals such as emission lines. This study conversely is based on a numerical model, developed in order to include altogether the effects addressed in the theoretical work to show combined effects on complex spectra like those expected from Mars. This allows not only to evaluate the linked effects of many kinds of disturbances but also to account for the real spectrometer characteristics. The use of synthetic spectra as input allows the comparison between expected spectra and measured ones. The simulation is tailored on the Planetary Fourier Spectrometer (PFS), onboard the ESA Mars Express spacecraft, from 2003 orbiting around Mars and in particular on its short wavelength (SW) channel, where many disturbances are more evident. © 2010 Elsevier Ltd. All rights reserved
A high resolution virtual AD converter
No full textData acquisition boards have been widely used in recent times as well as a dramatic decrease in costs and improvement of speed performances. The most common architecture of low-cost boards has one converter and a multiplexing system with variable gains. Such boards allow very good flexibility in terms of amplitude and frequency rates, but have the problem of non-simultaneity of channel sampling. At the same time most boards have a 12 or 16 bit resolution that in many cases in acoustics and vibrations are satisfactory. The method proposed in this work based on software algorithms, leveraging on low cost boards, permits a relevant improvement in resolution of data conversion and the synchronization of multiplexed channels
A new method for measurement of acoustic efficiency of classic guitars
No full textOne of most relevant limitations of acoustic guitar (that cannot be electrically amplified) is the low power of its sound, which very often can hardly be heard by the audience. No methods exist for quantitative evaluations of such feature and this make researches in this field particularly difficult, since it's impossible to compare an instrument to another. An effective and reliable method for measurement of acoustic efficiency of guitars and most other stringed instruments is presented, with some experimental result. The measurement approach of the method leads to a repeatability of about 4% in results
Uncertainty in end-point tension measurement in wires subject to high-velocity impact
No full textThis paper analyses sensor performance requirements in measuring end-point tension (in magnitude and direction) in cables subject to high-velocity impact. The work may be viewed as a tool to analyse and design end-point tension measurement devices for cable-like systems when wire dynamics is very rapid (> 10 kHz) and fully non-linear. Load effect, conversion time and ADC quantization effects are analysed in order to provide a full description of these uncertainty sources by simultaneous integration of the set of hyperbolic partial differential equations governing cable motion, and the set of ordinary differential equations describing the motion of the impacting object and sensor dynamics. Three-dimensional mathematical modelling of the wire is based on the theory of quasi-linear partial differential equations. Fully non-linear analysis of wire motion is thus accomplished without restrictions on displacement and deformation magnitudes. Numerical solution algorithms are based on the characteristics method. The main result is that the dynamic error due to sensor dynamics is the principal source of uncertainty. Moreover, the reduction of such uncertainty is not allowed by the actual force transducer devices, due to the high frequency response required. © 1995
Long term WBV measurements on vehicles travelling on urban paths
No full textThis paper describes the results of a long-term whole-body-vibration monitoring campaign performed on different cars with different drivers. The weighted and the un-weighted root-mean-square acceleration, the MTVV and the VDV have been monitored on five different cars in regular usage for over one hundred hours of measurements on urban roads and highways. The variability of the above parameters has been statistically analyzed in order to assess the time requested for the convergence of standard indexes to their average values. The aim is to supply a general reliability evaluation so as to minimize the on-field tests and to provide a scientific support to the design of such experiments. A comparison between different vehicles is presented and discussed; the correlation with speed measured by a GPS system is analyzed with probabilistic assessments. Results showed that the minimum time for reliable measurement was approximately 30 min for each driving condition (urban, carriage road, highway). The MTVV/aw ratio was usually larger than 1.5 (even on short measurement periods), thus indicating the unsuitability of the basic ISO 2631 criterion. The 8-h based VDV provided indications compatible with the av criterion
Contribution of airports to noise in surrounding environment; identification and measurement of noise sources
No full textThis paper describes the results of an experimental campaign carried out near the Milan Malpensa airport. Aim of the work was the determination of new parameters or measurements that can be used in order to deeply characterize the acoustic field in aeroportual environment. The most innovative aspect is the use of a three dimensional sound intensity probe, that allows determining the direction of the acoustic energy flow and consequently making assessments about the noise source position. Data has been statistically analyzed with sound intensity polar diagrams, which represent the direction of sound (as a function of frequency) coming from the surroundings toward the experimental site. These diagrams allow determining which is the direction from which most of the acoustic energy comes from and can be used, for example, in order to optimize active or passive noise control procedures
Sound source identification using coherence- and intensity-based methods
No full textVery often in environmental and industrial acoustics, it is necessary to identify the contribution of single sources to global sound levels. Under this perspective, interests arise from the necessity of controlling noise or verifying whether a single source exceeds legal limits while there are other active sources around. Currently available methods are typically based on coherence or expert system techniques. Both approaches have relevant limitations, but for current purposes, coherence methods are usually more robust, particularly if carried out using vibration sensors in vibroacoustic interactions. Nevertheless, when a measurement system has to be based only on microphone measurements, those methods also have too little reliability and unsatisfying accuracy. In fact, it is quite impossible to eliminate in the input signals the effects of other sources, which usually also have some coherence with the output signal. In this paper, a relevant enhancement to coherence-based methods is described and discussed. The proposed approach leverages on the use of an acoustic intensity measurement approach instead of the sound pressure one. Method advantages and limitations are addressed with a theoretical approach; method performances are experimentally verified. © 2007 IEEE
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