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Gabriele D’Antona
UNCERTAINTY ESTIMATION BASED ON INVERSE MODELS: AN OPEN QUESTION

In measurement science and its technological application most of the measurement methods are indirect. In order to measure the unknown physical quantity y we have to develop a forward model which relates this quantity to another quantity x directly measurable: x → y. Often the measurement model available is of opposite nature, i.e. y → x. It is thus necessary to invert the available model; this operation in some cases can lead to unacceptable level of uncertainty on the results. This paper shows the properties of some algorithms for processing measured data using ill posed inverse models employed for determining the distribution of indirectly measured quantities. The inversion procedure requires regularisation techniques in order to limit the uncertainty affecting the indirect measurements.

Alexandru Salceanu, Liviu Breniuc, Mihai Cretu,Valeriu David
MONITORING RAPID VOLTAGE FLUCTUATIONS AND HARMONICS DUE TO OSCILLATOR AND RELAYS IN THE CORD CONNECTING THE EQUIPMENT TO MAINS SUPPLY

Dealing with the precompliance EMC emissions testing for a new fluxgate magnetometer, in order to comply with European norms EN 55022, we experienced some difficulties, three of them being addressed in this paper: a) Best compromise for the mains filter; operating with an own manufactured V-LISN and a pair of 1:1 high quality transformers, the dominant component (common or differential mode conducted emissions) could be identified. Determining the major component of the conducted emission, allow us to decide which element of the filter should be modified to achieve the better compromise “size versus reduction in the total emission”; b) Best decoupling option for the electromechanical relays, mainly involved in the power management scheme and in the auto-ranging function; c) Minimising the spectral energy at harmonics of the fundamental frequency of the oscillator with the switching power supply; by reducing the magnitude of the open loop gain (was utilized a capacitive divider), the feedback current was also decreased, with the immediate result of an improvement in the spectral envelope of the power supply current.

Alexandru Salceanu, Constantin Sarmasanu, Mihai Cretu
AN APPROACH FOR NEAR-FIELD MEASUREMENT OF RADIATED EMISSIONS FROM DIGITAL CIRCUITS

There are presented two E-field and two H-field, versatile, cheap and easy-to-use probes, the effective constructive solutions, the adopted calibration set-up and procedure for measuring their performance factors. As standard reference we used commercial available Agilent and EMCO probes. While trying to improve the EMC characteristics of the prototype of a fluxgate magnetometer, and in consequence near field measuring, problems were encountered. More or less successful attempts are discussed. Some useful techniques and recommendations when dealing with designing PCBs of sensitive equipments are presented.

Eleftherios Kayafas, Florin Sandu, Ioannis Patiniotakis, Paul Nicolae Borza
APPROACHES TO PROGRAMMING FOR TELE-MEASUREMENT

Introducing and solving some specific problems of remote access to experiments, the present paper has not only a generic (architectural) point of view, but also a practical one. Based on their previous experience in telemeasurement (SMTP / POP3 and LabView implementations), [1] and [4], the authors built an integrated solution for the "publishing of the test and measurement capabilities" based on Java / Data Socket (or WinSock) transfer for remote access and LabView / Component Works / Visual Basic for local management of the automated measurement centers. A very friendly wyswyg ("what-you-see-is-what-you-get") real time duplex control / monitoring was practically implemented in VB emulated panels of the instruments that can be tele-accessed via a web-page of the remote virtual laboratory, without the requirement of any special Test & Measurement skills at users’ level (allowing them to concentrate on the specific experiment that can belong to any field of engineering).

U. Pogliano, G.C. Bosco
THE ELECTROMETRIC AC-DC TRANSFER STANDARD AS PRIMARY STANDARD AT IEN FOR AC VOLTAGES FROM 300 V TO 1000 V

An electrometric AC/DC transfer standard has been built, which compares the equivalence between an AC and a DC voltage by an attracting force sensed by an analytical scale. The functionality and the stability of the instrument have been tested and the electromagnetic and mechanic effects have been analysed. Comparisons with thermal converters have shown that this instrument can be conveniently used to maintain the traceability for voltage beyond 300 V, in the frequency range from 1 kHz up to 100 kHz.

U. Pogliano
INCREASING THE MEASUREMENT ACCURACY AT LOW FREQUENCIES BY SUCCESSIVE EXTRACTION OF THE ABSOLUTE MEAN VALUE

A method for the precision measurement of the RMS value of a low frequency voltage signal is described in this paper. The method consists in one or more stages that perform basically the same function, even if they can differ for the level of accuracy required. Each stage performs: the determination of the absolute value as function of time and the extraction of its mean value. Actual realization by means of an electronic circuit shows that accuracy at the level of 1 part in 104 can be easily reached.

Luciano Brunetti
ACCURACY ASSESSMENT IN HF POWER METER CALIBRATION

The paper analyses the classical procedures have to be performed for calibrating power meters having coaxial power heads. These procedures are intended for commercial power meters used by all measurement laboratories, nevertheless they include references to the specific measurement set-up used by the Italian primary measurement laboratory, that is IEN. The paper is aimed to provide technical documentation, that eases the unification of the measurement accuracy assessment in all the laboratories accredited or requiring accreditation by Italian calibration service (SIT).

Balázs Fock, István Zoltán
SELF-CORRECTING AC AMPLIFIER WITH INDUCTIVE DIVIDER

In this paper a self-correcting method is presented to reduce the error of an inverting amplifier below 20 ppm in 0-3 kHz frequency range. The method is based on a two step approch. In the first step the phase error of the amplifier is corrected, and then the methode is extended to the amplitude error reduction.

A. Tsirikos, P. Bougas, K. Gotsis, C. Meletis, J. Sifnaios, K. Z. Pekmestzi, G. Manis
A SUBMARINE LOW-POWER SHIP PROPELLER STRAIN MEASUREMENT SYSTEM

In this work the development of a custom submarine data acquisition system for the measurement of ship propeller strain is presented. The system measures the strain applied to 120 Ohm quarter bridge strain gauge sensors. It supports up to 15 acquisition channels, each with its own sensor, signal conditioning and 10-bit A/D converter, sampled at 500 Hz. The system features all necessary analog and digital subsystems needed to perform the signal conditioning, acquisition and data storage. The main features of the system include low power consumption using sophisticated power management, compact design based on a multi-processor architecture, high measurement accuracy, low-cost and robust autonomous operation. The system can be easily extended for applications where a telemetry system with stand-alone operation is needed.

Barton Zdenek, Vrba Radimir
DRIVER FOR LOW POWER THERMOELECTRIC SENSOR TEMPERATURE STABILISING COOLER

A new thermoelectric cooling system (TEC) was developed based on the Peltier. The driver drives the TEC (a Peltier element) to keep the temperature of the device under test (a laser diode) at a constant value. A NTC thermistor (placed in close contact to a device under test) measures the temperature. The Peltier driver consists of an input resistance bridge, an error amplifier, a PI regulator and a driver. The long time stability and the temperature stability of the Peltier driver itself are excellent. The Peltier driver can be implemented on-chip, too. Only a few external components should be necessary to use. Also a digital setting of the temperature can be implemented easily.

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