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This paper describes a system for the measurement of the internal and external temperature profiles of PET preforms used in the Injection Stretch Blow Moulding (ISBM) process. Many works in literature highlighted the importance of these quantities to improve the production quality of PET bottles, but none addressed the development of a measuring system suitable for this scope. A measuring system based on two thermopiles for the identification of the internal temperature profile and a thermal camera for the measurement of the external one has been designed. The adopted sensors were individually calibrated and the uncertainty budget, accounting for both instrumental uncertainties and the effect of multiple reflections, was derived. A prototype of the measuring system was tested on an industrial ISBM machine. The dependence of the preforms temperature profile on the settings of the ISBM machine was investigated. Results evidenced that the minimum variations of the machine settings induced temperature differences significantly larger than the measurement uncertainty, thus proving the effectiveness of the proposed system.

A compact and light-weight set-up to impose medio-lateral vibration while walking has been designed and manufactured. A vibrating plate was actuated by a motor and a linear guide. After the design and finite-element analysis, the set-up has been manufactured and tested in the frequency band 0.5-4 Hz with amplitude below ± 20 mm, that is compatible for human testing. Total harmonic distortion has been measured below −30 dB. Crosstalk values along Z and Y measured at the corners of the moving platform were lower than 0.1 at 4 Hz. Given the previous analyses, the set-up can be used to test in a movement laboratory the effect of vibration during walking, mounting a walking pad on the platform.

This paper focuses on the different sensors and signal processing techniques to identify the working conditions of a hydraulic block. A Laser Doppler Vibrometer and a microphone are used to identify the sound pressure and the vibration velocity on the valve body. Tests showed that it is possible to identify different pressure and flow conditions through relying on time-frequency aggregated parameters.

An intelligent thrust reverse noise detector is presented in this paper (TREND).A first detector is customized for the detection of landing sound events. When one of those events is detected, a second detector is triggered to detect thrust reverse. In the case that both events are detected, each of them have to be classified in two separate block. If the first events is classified as landing, and the second one as thrust reverse, the system identifies the activation of thrust reverse. The detection is based on thresholds applied to the sound power level (instead of sound pressure level in the traditional approaches) time histories, which are estimated using a microphone array and an inverse sound propagation model. This approach has worked well, as the estimation of sound power level enhances the sound events and their separation, even if landing and thrust reverse are close to each other. The classification is implemented through pattern recognition techniques, which reduces the number of false positive in the detection stages. The results obtained in Madrid-Barajas airport through the implementation of the methodology in this TREND tool are promising with error rates lower than 10%.

A thrust reverse noise detection methodology for airports is developed and tested in terms of meeting the restrictions at Madrid-Barajas airport. The detection is based on thresholds applied to the sound power level time histories estimated using a microphone array and an inverse sound propagation model. The two sound events detected are classified as landing and thrust reverse to complete the identification of thrust reverse activation. The methodology performs well especially in the detection stage because the estimation of sound power level enhances the sound events and their separation, even if landing and thrust reverse are close to each other. The implementation of the TREND tool has error rates lower than 10%.

This paper evaluates the advantages and the drawbacks deriving from the use of MEMS (micro-electro-mechanical systems) accelerometers for hand-arm and whole-body vibration measurements. Metrological performances of different transducers were assessed through the identification of their frequency response function, linearity, floor noise and sensitivity to thermal and electromagnetic disturbances. Experimental results highlighted a standard instrumental uncertainty (including the nonlinearity) lower than 5% with the single frequency calibration procedure, such a value was reduced to 2%. The temperature effect was negligible and the electromagnetic disturbances sensitivity was comparable to that of the piezoelectric accelerometers. The compatibility of measurements obtained with MEMS accelerometers with those of piezoelectric-based measurement chains was verified for two specific applications. An example of direct transducer fixation on the skin for vibration transmissibility measurements is also presented. Thanks to the MEMS peculiarities – mainly small sizes and low cost – since novel approaches in the vibration monitoring could be pursued. For instance, it is possible to include by design MEMS accelerometers in any hand-held tool at the operator interface, or inside the seats structures of cars, tractors and trucks. This could be a viable solution to easily obtain repeatable exposure measurements and could also provide diagnostic signals for the tools or seats of functional monitoring.

The long-term exposure to vibrations transmitted to the human upper limb by hand-held powered tools leads to a group of diseases commonly known as hand-arm vibration (HAV) syndrome. The risk deriving from the vibration exposure can be assessed with direct measurements, using data declared by the tool manufacturer or by retrieving measurements from specific databases. The discrepancies between data belonging to each of these three groups were evidenced in several studies. This paper analyzes the causes of the HAV measurements variability following the ISO GUM approach. The work process was modeled with a lumped parameter scheme of the tool–operator–measurement chain interactions. The measurement uncertainty has been identified propagating the uncertainties of the influencing parameters through the model. The soundness of the approach was verified by comparing the predicted and the observed variability in a specific case study. The major outcome of the proposed method is that the uncertainty budget allows understanding which parameters have to be controlled to limit data dispersion.

In mountain-rescue operations injured people are generally exposed to vibrations and shocks that can be potential causes of physical conditions worsening. Such vibrations can derive both from patient's body manipulations (e.g. when it is being loaded and immobilized on a stretcher) and from forces coming from the transport devices and vehicles. Despite the general feeling that during this kind of operations the levels of transmitted vibrations to the injured can be quite large and potentially dangerous, there is practically no study in literature providing reliable parameters (i.e. measurements) to support or dismiss these beliefs. This paper reports the results of a measurement campaign carried-out in order to outline, identify and quantify the excitations a human body is exposed to, during typical transportation phases related to mountain-rescue operations. The work mainly presents and discusses the experimental setup with the aim of focusing on the problems related to this kind of measurements; the results of the experimental campaign carried-out for the measurement of the vibrations undergone by a human body during a simulated rescue operation are presented and discussed as well. Such simulation includes three phases of transportation: on a hand-held stretcher, on an ambulance and on a helicopter. The work is not intended to supply a complete characterization and analysis of vibrations transmission during any rescue operation but just to provide a preliminary overview and to define a measurement method that can be applied for a more comprehensive characterization. With such aims measurements were carried out in on-field situations stated as “typical” by rescue experts and data then analyzed both with standard procedures and algorithms (e.g. ISO 2631s weighting curves) and with the commonly used statistical indexes; in the analysis it is important to be aware that standardized measurement procedures and indexes, created to verify comfort or health-risks of workers, might not fit the case of a generic patient who experienced a serious mountain accident. The work includes also a laboratory activity mainly related to mechanical characterization of the stretcher used in the field tests. The most interesting result of the study is the comparison of the vibration levels in the various rescue phases that, even when using different indicators, shows that the most critical issue is due to hand transportation despite the bad judgment usually expressed for helicopter flight.

Many airports all over the world have established restrictions for the use of thrust reverse for slowing down aircraft after landings, especially during the night period, as a way of reducing noise impact and the number of complaints in the vicinity of airports. This is the case of Madrid airport, where the Universidad Politécnica de Madrid, in collaboration with AENA, and the Politecnico di Milano have been researching, and developing intelligent instruments to improve the detection and classification of thrust reverse noise among other noise sources present in the airport. Based on a traditional approach, the thrust reverse noise detection tool detects two consecutive sound events, and applies pattern recognition techniques for the classification of each of them (such as landing and thrust reverse). A second improvement refers to the use of a microphone array linked to a noise- monitoring unit, which enables tracking the direction of arrival of the sound, thus improving the classification rates. By taking the latter, it is also possible to track the aircraft location along the runway, which enables sound pressure measurements to be transformed into sound power level estimations. Although the novel instrument can still be optimized and customized, the results have shown quite good classification rates (over 90%).

The human response to vibration is typically studied using linear estimators of the frequency response function, although different literature works evidenced the presence of non-linear effects in whole-body vibration response. This paper analyses the apparent mass of standing subjects using the conditioned response techniques in order to understand the causes of the non-linear behaviour. The conditioned apparent masses were derived considering models of increasing complexity. The multiple coherence function was used as a figure of merit for the comparison between the linear and the non-linear models. The apparent mass of eight male subjects was studied in six configurations (combinations of three vibration magnitudes and two postures). The contribution of the non-linear terms was negligible and was endorsed to the change of modal parameters during the test. Since the effect of the inter-subject variability was larger than that due to the increase in vibration magnitude, the biodynamic response should be more meaningfully modelled using a linear estimator with uncertainty rather than looking for a non-linear modelling.

This work describes the results of an experimental campaign whose aim was the identification of the hand-arm driving point mechanical impedance (DPMI) in presence of a stimulus having an unknown direction. This situation is relevant in case of cylindrical handles, where the tool can be gripped in different ways independently from the vibration direction. In this case, x h and z h ISO 10068 curves can be conveniently substituted by a unique parameter, here referred to as “radial impedance”. Radial impedance values have been determined with an experimental campaign based on the classical setup in which the vibration is generated by an electrodynamic shaker and the force component parallel to the vibration is measured by an instrumented handle. The vibration direction was always vertical, while the different postures entailed a different stimulus orientation with respect to the hand, forearm and shoulder. The hand-arm posture was monitored using a purposely designed measurement system. The push forces transmitted by the operator to the handle were measured using load cells, while the grip force was measured before the tests using a pressure matrix. A statistical analysis on the radial DPMI data was performed using the analysis of variance (ANOVA) techniques. Results showed that the uncertainty deriving from the adoption of the radial impedance in presence of cylindrical handles does not always lead to a larger uncertainty with respect to the ISO 10068 data. Coherently with the existing literature studies, also the radial DPMI depends on the forces transmitted to the handle and on the wrist, elbow and shoulder postures. The opportunity of adopting (in specific cases) the radial impedance instead of the x h and z h is discussed. Relevance to industry Hand-transmitted vibration may cause a variety of vascular and musculoskeletal disorders that often result in loss of work capacity and compromised quality of life. The concept of radial impedance described in this paper can be used in the design of devices meant to reduce the vibration transmitted to the workers, thus reducing the above mentioned risks.

A common issue in the design of measurement instruments is the comparison between different solutions in terms of components of the measurement chain, data processing or even measurement principles; the predicted instrumental uncertainty is the driving parameter for such a comparison. While in many situations the linearization of the measuring model allows using the standard ISO GUM procedure, in complex cases it might be necessary to proceed with Monte Carlo simulations as per ISO GUM supplement 1. This paper describes a method that combines the factorial design of experiments (DOE) and the ISO GUM supplement 1 uncertainty evaluation method to guide the instrument designer in the instrument configuration optimization. The proposed approach allows estimating, in the design phase, the overall instrumental uncertainty for different configurations, the instrument sensitivity to the accuracy in the measurements of its inputs and the effects on systematic and random measurement errors deriving from the choice of all instrumental variables. The use of data populations selected with the DOE criteria allows recovering valuable parameters equivalent to the sensitivity factors of the GUM linearized approach. The data analysis allows separating the critical factors that must be accurately controlled from those only weakly affecting the measurement uncertainty. The method has been applied to a case study where the metrological performances of a system devoted to the measurement of the acoustic radiation emitted by a vibrating panel in a reverberant enclosure had to be assessed.

One of the most important issues in aircraft noise monitoring systems is the correct detection and marking of aircraft sound events through their measurement profiles, as this influences the reported results. In the recent ISO 20906 (unattended monitoring of aircraft sound in the vicinity of airports) this marking task is split into: detection from the sound level time history, classification of probable aircraft sound events, and the concluding identification of aircraft sound events through non-acoustic features. An experiment was designed to evaluate the factors that influence the marking tasks and quantify their contribution to the uncertainty of the reported monitoring results for some specific cases. Several noise time histories, recorded in three different locations affected by flyover noise, were analyzed by practitioners selected according to three different expertise levels. The analysis was carried out considering three types of complementary information: Noise recordings, list of aircraft events and no information at all. Five European universities and over 60 participants were involved in this experiment. The results showed that there were no significant differences in the results derived from factors such as the participant's institution or the expertise of the practitioners. Nonetheless, other factors, like the noise event dynamic range or the type of help used for marking, have a statistically significant influence on the marking tasks. They cause an increase of the uncertainty of the reported monitoring and can lead to changes in the overall results. The experiment showed that, even when there are no classification and identification errors, the detection stage causes uncertainty in the results. The standard uncertainty for detection ranges from 0.3 dB for those acoustic environments where aircraft are clearly detectable to almost 2 dB in more difficult environments. © 2011 Elsevier Ltd. All rights reserved.

This paper describes a method that allows accuracy and bandwidth enhancements in 3D sound intensity measurements. Commercial 3D probes are usually set up with three mutually perpendicular 1D p-p probes and, thus, arranged with six microphones; although sound intensity can be calculated with 15 independent pairs of transducers, only the three "primary" pairs that are aligned with the coordinate system axes. The other 12 "secondary" pairs consist of mutually perpendicular microphones, which are placed at a distance that is radic2 times shorter than the primary one. The main idea of the proposed method is to average the intensity that is measured on primary and secondary pairs. This leads to a larger bandwidth, thanks to the shorter separating distance between secondary pairs. The intrinsic p-p method high- frequency sensitivity loss is partially recovered, starting from the theoretical plane wave expression. Measurements of different axes are weighted with coefficients that are computed by optimizing the measurement uncertainty. Errors that are due to the metrological characteristics of the transducers and the effects of environmental conditions are compensated. Experimental results showed that a p-p probe arranged with half-inch microphones that are placed at a distance of 50 mm allows reliable measurements up to 2.5 kHz, whereas a commercial probe bandwidth with the same configuration is usually 1250 Hz.

Small pneumatic hammers are largely used in the processing of stony materials, both for artistic and building purposes. These tools are characterized by the alternative movement of the instrument (chisel, bush hammer, etc...) and vibrations at the handle are particularly relevant. An italian factory (Torneria Aloisi Luciano & C., Verona) has designed a prototype in order to reduce the vibrations transmitted to the operators. Such a prototype has been characterized by the authors both in working conditions and in laboratory. Experimental results have shown relevant reduction in the vibration transmitted to the operator.

Accelerometers saturation may occur when measuring mechanical events characterized by a wide frequency bandwidth. The problem usually arises when the mechanical vibration frequency band exceeds the accelerometer bandwidth. Mechanical filtering is then a smart technique to reject undesired contribution above a certain cut-off frequency and avoid transducer saturation. Commercially available mechanical filters exhibit limits, in particular regarding cut-off frequency selection and insertion error. This paper describes a method to realize a mechanical filter that takes advantage of the mechanical link between the vibrating surface and the accelerometer to obtain the user-demanded characteristics for both mono-axial and tri-axial accelerometers. The designed filter Frequency Response Function is first estimated by means of Finite Elements Method simulations, and then experimentally verified. The effects of temperature and aging on filter performances are also presented.

This paper presents the activities performed for the modelling and experimental characterisation of a pyroelectric infrared detector. The work focuses on a LiTaO3 sensor which has been used as detector in the Long Wavelength Channel of a double channel IR spectrometer devoted to the study of Mars atmosphere, the MarsExpress Planetary Fourier Spectrometer, PFS. The need for an experimental characterization arise from the need of modelling the complete spectrometer for a correct interpretation of the scientific data collected while orbiting around Mars. The sensor of interest has been characterised along with its amplifying and conditioning proximity electronics. Because of the final use of the detector, i.e. FTIR spectrometry, the experimental characterization focuses on the frequency response and non-linear behaviour which respectively affects spectral responsivity and the presence of spectral features ghosts. Mathematical models available in literature describing the pyroelectric phenomena usually neglect the dependence of thermal characteristics on temperature and are intrinsically linear, therefore unfit for our needs. Because of the lack of information about the detector building characteristics, an accurate a priori model could not be straightforward implemented. An a posteriori model, derived from an identification process based on the detector testing has been developed and validated in order to have a simulation tool for the full spectrometer. The sensor exhibit nonlinearities, depending on all factors influencing the sensing element average temperature: incident infrared power, housing temperature. These nonlinearities can be traced back to the dependence on temperature of thermal characteristics of the sensing element, pyroelectric coefficient and the thermal capacity of LiTaO3 and on the nonlinearity of the radiative heat exchanges.

Sound intensity can be evaluated by means of pressures measured by two microphones. With the use of four or six microphones one can measure the three-dimensional sound intensity vector. Measurements carried out in this way are subject to errors due to various causes. Aim of this paper is to describe a novel method (based on virtual instruments) for a real time correction of such errors. The correction algorithm compensates errors due to metrological characteristics of the transducers and measurement chain: sensitivity, phase response, microphone directional characteristics and interchannel delay. The effects of environmental conditions, namely pressure, humidity and temperature, can also be compensated.

One 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 results. The measurement approach of the method leads to a repeatability of about 4% in results.

Sound and vibrations problems sometimes require long term monitoring, especially when dealing with complex phenomena. It often happens that annoyance to people or - generally - noise pollution to surrounding environment can be caused by particular conditions of sources which occur somehow randomly. In these cases, in order to understand the causes of problems and solve them, it's fundamental to perform multi-sensorial measurements on phenomena themselves and on possible causes and trace their behavior for long periods. So as to perform such issues authors have developed a virtual instrumentation-based measurement system which can collect and on-line analyze data from several sound, vibration and other generic channels for months-long periods. In this paper the measurement system will be shortly illustrated and results of a measurement campaign that the Politecnico di Milano carried out in a thermo-electrical power plant in Northern Italy will be presented as an example of application.

In theaters and halls reflections play a key role in sound quality. The experimental characterization of reflected components of sound is very difficult and classical measurement techniques are not generally very effective. A new method for sound reflection time measurements without the problems of existing techniques, is illustrated in this paper, with some experimental results.

Patch near-field acoustic holography (NAH) coupled with an array of sound intensity probes allows separating the sound field incident on a surface from the one radiated by the surface itself. Although the measurement principle has been successfully used to separate the noise source contribution from disturbing sources and/or noise reflections, the method accuracy has not been investigated in the literature. We describe the results of experiments meant to evaluate the uncertainty in the identification of noise radiated by vibrating panels with different absorption characteristics in presence of an incident acoustic radiation using the statistically optimized near-field acoustic holography. Measurement errors were evaluated through tests performed in controlled acoustic conditions. Results evidenced that the measurement uncertainty depends on the accuracy of the microphone array positioning and on the incident sound field. These conclusions were in agreement with the results obtained by simulations in the phase of instrument optimization.