New Generation of Crystal Quartz Thin-Film Multijunction Thermal Converters
The design of a new generation of planar multijunction thermal converters (PMJTCs) on quartz membranes and on quartz crystal chips improves the frequency response of the PMJTC in the frequency range from 100 kHz to 100 MHz and allows a decrease in the uncertainties. For a heater resistance of 1 kOmega ac-dc voltage transfer differences smaller than 5 muV/V are calculated for frequencies above 100 kHz up to 1 MHz. This is a reduction of more than one order of magnitude in the ac-dc voltage transfer differences for such high heater resistance in comparison to the PMJTCs with Si3N4/SiO2/Si3N4 sandwich membrane on a silicon chip. The quartz PMJTCs allow the improvement of the standard uncertainties to 3 muV/V in the frequency range of 100-500 kHz and 5 muV/V for 700 kHz to 1 MHz. The model for calculating the ac-dc voltage transfer differences and the uncertainty budget are given
APMP international comparison of AC-DC transfer standards at the lowest attainable level of uncertainty
This paper presents preliminary results of the APMP.EM-K6a key comparison of AC-DC transfer conducted during 2000 to 2003. The AC-DC voltage transfer difference of the travelling standard was measured at 3 V and selected frequencies from 1 kHz to 1 MHz that included those of the CCEM-K6a key comparison. Also discussed are the methods used to compare thermal voltage converters with different input connectors, and to link the results to the parent Consultative Committee on Electricity and Magnetism (CCEM) comparison.
Reduction of patient exposure during dental radiography.
We investigated the effect of using additional accessories with a conventional X-ray machine to reduce patient exposure during full-mouth dental radiography. LiF extruded-rod thermoluminescent dosimeters were placed in 23 anatomical sities of a Randophantom and the phantom was exposed to a Turkish dental X-ray machine operated at 60 kV, 10 mA for 0.5 sec periods. Maximum reductions were observed at the eyes (80%), in the thyroid (70.6%). under the collar bone (59.9% average) and the gonads