Power meter for Highly-Distorted Three-Phase Systems

This paper describes a low-cost, three-phase power meter, which is based on a fast, specially designed acquisition board coupled to a PC via the PC parallel/printer port or by means of an AT card. The power associated with the fundamental and first harmonics is computed by software that operates in the time domain and employs a sample-weighting procedure that makes the uncertainty related to the asynchronous sampling negligible. The low-cost acquisition board features two 8-bit 1 MHz converters and a local RAM, which decouples the PC clock from the measurement requirements. Hall effect transducers are used for the current channels and fast differential amplifiers for the voltage channels. The fast sampling frequency allows simple antialiasing filters to be employed. Digital filtering is used to reduce the sample number while increasing the resolution. The power uncertainty provided by this arrangement is less then 0.1 % with 2.5 measurements per second when a low-cost 486DX33-based PC is use

An Ultrasonic Sensor for Distance Measurement in Automotive Applications

This 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

A Remotely Controlled Calibrator for Chemical Pollutant Measuring-Units

The increasing diffusion of pollutant measuring units, which are installed over wide areas, along with the short calibration interval of several sensors for pollutant quantities, requires new calibration infrastructures to be developed. This paper describes an attempt to develop an innovative calibration system which is based on traveling standards and which does not require units to be removed from the measuring site during the calibration process. The calibration system is based on a traveling standard, which is composed of one or more cylinders that contain gas mixtures, a cell with standard sensors, and a control unit with networking capabilities, which allows the traveling standard to be remotely exercised. A prototype of the proposed system is described and the preliminary results reporte

Measurement Procedures for the Electrical Characterization of Oxide Thin Films

This paper describes a measurement system for the electrical characterization of oxide thin films. Such films can be produced using plasma-sputtering processes and permit the realization of a large set of high-performance components, such as capacitors, active devices, sensors, and protective coatings. The electrical properties of the oxide films, which have a thickness of less than 1 μm, are difficult to measure since very high resistances (on the order of gigaohms) and small capacitances (on the order of picofarads) are expected for contact areas smaller than 1 mm2. The measurement system and the procedures described in this paper represent an alternative solution to the commercial devices, which usually employ a mercury probe for performing the contact with the specimen under characterization. Furthermore, the proposed system can be used not only to estimate the electrical properties of a single point but to evaluate the uniformity of oxide films on large specimens as well. The experimental results reported refer to valve-metal-based oxide films deposited in a lab-scale capacitively coupled parallel-plate reactor and show the effectiveness of the proposed procedure

A Traveling Standard for the Calibration of Data Acquisition Boards

The large use of measurement systems based on data acquisition boards makes the traceability-chain assurance a tricky problem due to the difficulty in consistently calibrating such boards. In this paper, the authors describe a traveling standard which can be used for the calibration of many commercially available acquisition boards. By employing such a traveling standard, the calibration procedure can be remotely exercised by a calibration laboratory through the personal computer which hosts the board that has to be calibrated. In such a way, the calibration results refer to environmental, software, and hardware conditions that exactly match the board-operating conditions. Furthermore, the board unavailability time is drastically reduced, with a consequent economic advantage for the board owner. The traveling standard is based on a microcontroller which is responsible for the communication with the PC that hosts the board and for the board-stimulus generation, and on a digital multimeter, which acts as a reference standard

A Microwave System for Relative Humidity Measurement

This paper deals with a microwave hygrometer that is based on the sensitivity of air permettivity to humidity. The hygrometer embeds a microwave generator which feeds two different channels. A channel is a holed waveguide, whose permettivity depends on the air humidity, while the other channel is insensitive to the air humidity. The output signals of the two channels are suitably combined in order to obtain the corresponding phase angle, which depends on the permettivity of the air inside the holed waveguide and therefore on the air humidity. Two possible implementations of the proposed principle are described which permit one to obtain an uncertainty of a few percentage of relative humidity in the humidity range of 10% RH to 90% RH and in the temperature range of 5 °C to 40 °C, but with different costs and complexities. The main characteristics of the proposed sensor are a fast response, a low sensitivity with respect to air pollution and the absence of hysteresis phenomena

Measurement uncertainty issues in freeze-drying Processes

This 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

A Wireless Sensor Network for Cold-Chain Monitoring

This paper deals with a wireless sensor network that was specifically designed to monitor temperature-sensitive products during their distribution with the aim of conforming to the cold-chain assurance requirements. The measurement problems and the constraints that have been encountered in this application are initially highlighted, and then, an architecture that takes such problems into account is proposed. The proposed architecture is based on specifically designed measuring nodes that are inserted into the products to identify their behavior under real operating conditions, e.g., during a typical distribution. Such product nodes communicate through a wireless channel with a base station, which collects and processes the data sent by all the nodes. A peculiarity of the product nodes is the low cost, which allows the information on the cold-chain integrity to be provided to the final customer. The results that refer to the functional tests of the proposed system and to the experimental tests performed on a refrigerated vehicle during a distribution are reporte

Outdoor Experimental Laboratory for Long-Term Estimation of Photovoltaic-Plant Performance

This 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

In Situ Calibration of Heterogeneous Acquisition Systems: The Monitoring System of a Photovoltaic Plant

This paper deals with the metrological management of an acquisition system that has been developed for monitoring an experimental photovoltaic (PV) plant. The acquisition system has been conceived for comparing the performance of different PV technologies and for verifying the nominal specifications of the PV modules. For these reasons, the traceability of the monitoring system has to be ensured, and therefore, it must be periodically calibrated. A remotely exercised procedure is proposed for the calibration of the acquisition system, which is based on a calibrator specifically designed for this application. This calibrator has the capability to act as a reference for heterogeneous quantities, including electrical quantities, temperature, and solar irradiance. The architecture of this calibrator is described, and experimental results for the preliminary characterization of the prototype are described