1,721,232 research outputs found
Experimental design techniques for optimising measurement chain calibration
No full textThis paper tackles the design of a calibration using experimental design techniques. In particular, the optimum calibration plan for measurement chain is identified by suitably elaborating the error propagation law suggested by the ISO Guide. The main advantages of the proposed approach consist in: (i) calibration plans with a reduced number of calibration points; (ii) calibration curve applicable to the whole operating range; (iii) linear rather than complex regression technique always usable. Two different cases were analysed in order to show the efficiency of the proposed optimisation procedure: a psychrometer and an heat meter. The obtained theoretical results are verified on a number of real calibrations. © 2001 Published by Elsevier Science Ltd
Experimental investigation of the electromagnetic interference of ZigBee transmitters on measurement instruments
No full textThis paper deals with the electromagnetic susceptibility of measurement systems when subjected to interference generated by short-range, low-power wireless transmitters. A ZigBee transmitter was used as an interfering source operating close to the instrumentation under test. The results of numerous tests prove that different kinds of measurement instrumentation can be affected by the wireless module interference. Significant metrological performance decay was observed for both frequency- and time-domain measurements carried out by instrumentation whose bandwidth includes the ZigBee frequency operating range. © 2008 IEEE
How to use traditional spectrum analyzers for correct evaluation of the human exposure to electromagnetic fields generated by WiMAX devices
Full text linkWorldwide Interoperability for Microwave Access (WiMAX), based on the IEEE 802.16 standards, is a technology that offers low cost mobile broadband access to multimedia and internet applications for operators and end-users. Similarly to cellular phone or other Radio Frequency devices, WiMAX has to be considered as a possible source of electromagnetic pollution and so monitoring its emission could be necessary to verify compliance with the applicable emission limits. Generally, the monitoring of the electromagnetic pollution is performed by means of a suitable measurement chain constituted by an antenna connected to a traditionalspectrum analyzer. The use of this kind of device to measure the power of digital modulated noise-like signals, such as WiMAX, requires to use proper measurement methods and to carefully set many instrument parameters to obtain reliable measurement results, otherwise a significant underestimate or overestimate of the human exposure can be obtained. In this framework, this paper investigates the feasibility of using the traditional spectrum analyzer to perform the electromagnetic pollution measurements due to WiMAX devices. A large experimental campaign is carried out to identify the most proper measurement method and spectrum analyzer settings able to warrant reliable measurements. © 2010 Polish Academy of Sciences. All rights reserved
Experimental Investigation on Workers’ Exposure to Electromagnetic Fields in Proximity of Magnetic Resonance Imaging Systems
No full textThe paper presents the results of an experimental activity focused on the measurement of electromagnetic fields generated by magnetic resonance imaging systems, carried out with the purpose of assessing exposure of workers to static, low frequency and radio-frequency electromagnetic fields, as required by the EU Directive 2004/40/EC. The main contribution of the paper is that it presents a comparative study of exposure carried out during operation of the MRI system and close to the sources, with different scanning sequences and RF coils. Results show that the static magnetic field follows the theoretical values only close to the magnet due to the effect of the walls, with a few percent variation due to the operating conditions; exposure to the magnetic field in the low frequency band is mainly determined by emissions generated by the power grid at 50 Hz and by the pulses driving the gradient coils; and finally the radio-frequency band only shows contributions by the diagnostic pulses at the resonance frequency, with exposure levels usually below the limits contained in the Directive. © 2011 Elsevier Ltd. All rights reserved
PWM techniques for voltage source inverter: a comparative analysis in terms of EMC performances
No full textIn this paper, an accurate experimental investigation on several Pulse Width Modulated techniques for power converters feeding induction motors is described, with the aim of performing their comparison in terms of EMC performances. For this purpose, a test desk based on a voltage source inverter feeding a low power induction motor has heen assembled in an semianechoic chamber. Besides, a single board digital modulator, which executes all the PWM strategies under consideration, has been manufactured. By means of a suitable measurement set-up, all the dominant emission sources and signals in tbe converter have been identified for each modulation technique and compared
Multisensor Acoustical Systems: Calibration and Related Problems
No full textNowadays, acoustic antennas are used in different application fields with the primary aim of detecting the presence and the position of acoustic sources. The uncertainty in the evaluation of the acoustic source position is related to the knowledge of right acoustic locations of the microphones in the array, which is different from the geometric ones and needs a suitable calibration procedure to be evaluated. This paper, after an analysis of the problems related to the calibration of acoustic antennas, proposes a dedicated strategy with the aim of assessing an optimized experimental setup guaranteeing the best uncertainty in the acoustic source location
Influence of Wi-Fi computer interfaces on measurement apparatuses
No full textNowadays, low-power wireless technologies like Wi-Fi, ZigBee, Bluetooth, to cite a few, are often present in measurement environment. Sometimes, they can be considered as unwanted disturbances. Many times, they are used as communication medium to realize smart data transmission. Among them, Wi-Fi is the most widespread in the development of wireless local area networks (WLANs), and because of its good data transmission rates and plug-and-play capabilities, it is the main candidate for integrating measurement instruments in wireless networks. Although designed and developed to reduce at minimum its radiated emissions, Wi-Fi has to be considered as a potential interfering source for modern instrumentation that often has bandwidth and operating frequencies including the Wi-Fi band. For these reasons, a careful investigation on the electromagnetic susceptibility of measurement systems, when subjected to Wi-Fi, is carried out in this paper. Disturbance effects due to the Wi-Fi technology on typical measurement stations, including spectrum analyzers, digital oscilloscopes, universal counters, and digital multimeters, are analyzed. The achieved results prove that the effects of interferences due to the wireless module on modern instrumentation are often not negligible, thus potentially compromising its metrological performance and the measurement result reliability. © 2006 IEEE
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