A procedure for the metrological evaluation of the self‐heating effect in resistance thermometers is reported. This procedure is applied to different designs of resistance thermometers, used for meteorological and climate applications. The study of the self‐heating effect variation with the applied electrical current, temperature and different surrounding environments is described, as well as the influence of wind speed on the self‐heating effect.

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A new method to compare the Quantized Hall Resistance (QHR) with a conventional resistance standard is proposed. This new method uses a Binary junction programmable Josephson array specifically designed to have a center tap to simultaneously measure the voltage of the QHR and the test resistance. This new method is expected to compete in uncertainty with the Cryogenic Current Comparator at lower cost.

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38.400-902 -UberMir -MO -Brazil FAX 55 236 5099 -E-MAIL BATISTA@BRUFU.BmET ABSTRACT 1 -INTRODUCTION In recent years, various softswitching techniques have been presented for high-frequency switching circuits, to reduce the switching losses in classical DC-DC Pulse-Width Modulation Converters techniques are based on the existence of either Zero Current switching (ZCS) or Zero voltage switching (ZVS) conditione during switch commutation. The ZVS or ZCS techniques are possible only if load input and output voltage satisfy certain conditions. Particularly, the ZVS technique need a minimum load to achieve zero voltage in the resonant capacitor. If it isn't satisfied the switch will be damaged, because the resonant capacitor is in parallel with the switch [2] and [5]. This paper introduces a new Buck topology, whose features are Zero Voltage and Zero current switching, operation at constant frequency, regulation by Pulse width Modulation and low RMS current stresses on active devices. The main goal of this topology when compared with classical ZVS-PWM one is ability on working with a wide load range. In hard load it works like the conventional ZVS. On the other hand, in light load it works with very small commutation losses.The complete operation principle, theoretical analysis, design procedure, example and simulation will be present.A prototype operating at 100KH2, input voltage of 125V, rated at 400W (40V, 10A) has been successfully implemented. 121, r41, 151, [71 and 1 8 1 . ~h e a e (*I -Uiuvcnihdc Fulcrd de Santa Muir -CT -DELC 97.11 1-970 -S a w Maria -RS -Brazil E-MAIL LEAES@BRUFSM.BITNET