Ohm

Abstract: A continuously operating low dissipation system for sensing the electrical resistance of an element while the element carries a normal operating current. A pulse of electrical energy having a regulated ohm's law related first parameter is switched through the element while a second ohm's law related parameter of the element's response to the energy pulse is simultaneously measured. These two known parameters provide the information necessary to determine the element's resistance using Ohm's law. In the preferred embodiment voltage and current are used as the two parameters. The system is calibrated for the regulated level of the first parameter while the second parameter is amplified and stored in a sampling circuit for continuous display between pulses as an indication of resistance. The pulse techniques of this disclosure allow continuous operation of the system without heating of the resistive element or excessive power use. The resistance indication is additionally useful for indicating the remaining charge in a battery where the indicated resistance is the battery's internal resistance. A distinct battery terminal voltage indication is also given.

Abstract: Accessory mineral U–Pb geochronology by isotope dilution thermal ionization mass spectrometry (ID-TIMS) requires precise and accurate determinations of parent–daughter isotope ratios. The small sample size, particularly with respect to radiogenic Pb (Pb*), requires highly sensitive ion detection systems. Most studies therefore employ either secondary electron multipliers (SEMs) or Daly photomultipliers that provide low background noise and high sensitivity but have a limited linear range and require dynamic peak-hopping. We here evaluate the application of new 1013 ohm resistors in a Faraday cup amplifier feedback loop for the static collection of all Pb isotopes (sample and tracer) with 202,205,206,207,208Pb measured on Faraday cups and 204Pb measured in the axial SEM of a Thermo Scientific™ TRITON™ Plus TIMS instrument. We demonstrate long-term stability of the amplifier gain calibration using a secondary Nd standard and test short- and long-term stability and reproducibility of amplifier baselines. Accurate calibration of static detector arrays is demonstrated by repeated analyses of synthetic and natural U–Pb standards (ET100, Temora-2 and AUS_Z7_5) with variable Pb* (0.551 to 699 pg) and comparison with conventional dynamic ion counting data. Excellent agreement between the two detector systems for all analysed standards suggests that our static measurement routine with 1013 ohm resistors produces accurate and precise U–Pb isotopic data with superior external reproducibility. We anticipate that this new technique will push the frontiers of high-precision U–Pb geochronology and may represent a crucial advancement in the quest towards inter- and intra-laboratory reproducibility at the 0.01% level.

Abstract: A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck constant is established by the practical realization of the electrical units derived from the Josephson and the quantum Hall effects. We describe in this paper the fourth-generation watt balance at the National Institute of Standards and Technology (NIST), and report our initial determination of the Planck constant obtained from data taken in late 2015 and the beginning of 2016. A comprehensive analysis of the data and the associated uncertainties led to the SI value of the Planck constant, h = 6.626 069 83(22) × 10(-34) J s. The relative standard uncertainty associated with this result is 34 × 10(-9).