1,721,134 research outputs found
Metrological Management of Large-Scale Measuring Systems
No full textA quality-assurance model is proposed in this paper that is conceived with the aim of correctly manage large scale measuring systems in a sustainable way. Such systems are made up of interconnected hardware devices and software programs that are distributed over a large area and that act as single measuring systems. The proposed model is based on a network-assisted calibration procedure, which allows both hardware and software sections of a large scale measuring system to be contemporaneously verified. Such a calibration procedure requires the availability of programmable traveling standards, which are sent to each measuring unit and are remotely controlled through the Internet. An application example is also described that refers to the metrological confirmation of DAQ-board based measuring system
An Ultrasonic Sensor for Distance Measurement in Automotive Applications
Full text linkThis paper describes an ultrasonic sensor that is able to measure the distance from the ground of selected points of a motor vehicle. The sensor is based on the measurement of the time of flight of an ultrasonic pulse, which is reflected by the ground. A constrained optimization technique is employed to obtain reflected pulses that are easily detectable by means of a threshold comparator. Such a technique, which takes the frequency response of the ultrasonic transducers into account, allows a sub-wavelength detection to be obtained. Experimental tests, performed with a 40 kHz piezoelectric-transducer based sensor, showed a standard uncertainty of 1 mm at rest or at low speeds; the sensor still works at speeds of up to 30 m/s, although at higher uncertainty. The sensor is composed of only low cost components, thus being apt for first car equipment in many cases, and is able to self-adapt to different conditions in order to give the best result
Measurement uncertainty issues in freeze-drying Processes
Full text linkThis paper deals with problems that have to be faced when performing mass and temperature measurements of substances subjected to freeze-drying processes. A brief description of a lyophilization process is initially presented and a deep investigation is performed in order to identify the main uncertainty contributions that affect mass and temperature measurements. A measurement system is then described that has been specifically conceived to work inside a freeze-dryer. Experimental results are reported that refer to the metrological characterization of the proposed measurement system and to its use for the monitoring of real freeze-drying processes. Experimental tests are also described that have been conceived to estimate the uncertainty contributions strictly related to this specific applicatio
Impedance measurement technique based on sine-fit
No full textAn impedance measurement system that is based on a voltmeter with digitising capabilities and on a sine-fit processing is proposed in this paper. The system can be arranged by employing standard instruments that are commonly available in calibration laboratories for the measurement of other electrical quantities. Two different solutions are proposed that differ in the used standards. One solution employs a multifunction calibrator that feeds the unknown impedance and a digital multimeter that acquires the voltage signal across the impedance; the other solution employs the same digital multimeter and a standard resistor in order to estimate the current that flows through the unknown impedance. In both cases the acquired samples are processed according to a four-parameter sine-fit algorithm. The system the authors have arranged allows impedance measurements in the frequency range of 40 Hz to 5 kHz to be obtained with expected standard uncertainty of about 0.04 % on the amplitude and of a less than 0.06 º on the phas
Outdoor Experimental Laboratory for Long-Term Estimation of Photovoltaic-Plant Performance
Full text linkThis paper describes an outdoor experimental laboratory that has been developed to estimate the performance of photovoltaic (PV) plants in operating conditions. The laboratory includes ten different plants and a data acquisition system that has been specifically conceived to monitor the actual behavior of the plants. The main goals of this laboratory are the comparison among the performance indexes of different PV technologies and the long-term drift estimation of the specifications of the plant components. In this paper, the first results that refer to a time interval of nine months are reported, which allow a comparison among the monitored PV plants to be performed. A description of the data-acquisition system is also provided by focusing attention toward its metrological management, which allows traceable results to be obtained that are qualified in terms of measurement uncertaint
Fast impedance analyser for corrosion monitoring
No full textFrequency Response Analysers (FRA) are commonly employed to monitor the corrosion state of metallic antiquities. Commercial devices, though very accurate and versatile, are often rather costly and require a long time to complete the Electrochemical Impedance Spectroscopy (EIS). This paper describes a low cost and portable alternative to commercial FRAs that also embeds the potentiostatic function and therefore can be used in the field without requiring external devices. The proposed instrument is based on a compact DSP board and employs a sine-fit algorithm for the impedance measurement; the paper also describes a fast algorithm to obtain the results without requiring long measuring sessions. The proposed instrument automatically performs a simple coating test and is equipped with a digital interface so that it can be connected to a personal computer to carry out a complete frequency analysis and to perform more complex data processin
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