Development of a four-channel system for Johnson Noise Thermometry
ABSTRACT Long integration time is necessary to reach low uncertainty when measuring temperature through Johnson Noise Thermometry (JNT). The main goal of the NIST JNT experiment is to achieve a 6×10-6 relative uncertainty in the measurement of the water triple point, which could contribute to the re-determination of Boltzmann's constant. A four-channel JNT system, which will reduce the measurement time two-fold, is being developed with new components, including a switchboard, an analog to digital converter (ADC) and a programmable, recharging power supply system. While implementing the new ADC, a source of systematic error was revealed, as well as a means to increase the measurement bandwidth.
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ABSTRACT: The Boltzmann constant was measured by comparing the Johnson noise of a resistor at the triple point of water with a quantum-based voltage reference signal generated with a superconducting Josephson-junction waveform synthesizer. The measured value of k = 1.380651(18) \times 10^-23 J/K is consistent with the current CODATA value and the combined uncertainties. This is our first measurement of k with this electronic technique, and the first noise thermometry measurement to achieve a relative combined uncertainty of 13 parts in 10^6. We describe the most recent improvements to our Johnson Noise Thermometer that enabled the statistical uncertainty contribution to be reduced to seven parts in 10^6, as well as the further reduction of spurious systematic errors and EMI effects. The uncertainty budget for this measurement is discussed in detail.Metrologia 12/2010; 48(3). DOI:10.1088/0026-1394/48/3/008 · 2.04 Impact Factor
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ABSTRACT: Long integration periods are necessary to reach low uncertainty when measuring temperature through Johnson noise thermometry (JNT). The main goal of the National Institute of Standards and Technology JNT program is to achieve a combined relative uncertainty of 6 × 10-6 in the measurement of the water triple point temperature, which, in turn, allows determination of Boltzmann's constant at the same uncertainty. To this end, a four-channel JNT system, which will reduce the measurement period twofold, is being developed with new components, including a switchboard, analog-to-digital converters (ADCs), and a programmable recharging power supply system. A significant source of systematic error that was discovered while implementing the new ADCs is described. New measurements are presented using a doubled ADC sampling rate, which show the potential for higher measurement bandwidth.IEEE Transactions on Instrumentation and Measurement 07/2011; 60:2655-2659. DOI:10.1109/TIM.2010.2098110 · 1.79 Impact Factor
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ABSTRACT: We have developed a quantum voltage noise source (QVNS) based on pulse-driven Josephson arrays and optimized its waveform synthesis for use with Johnson noise thermometry (JNT). The QVNS synthesizes multitone waveforms with equal amplitude harmonic tones and random relative phases in order to characterize the amplitude-frequency response of the analog and digital electronics of the JNT system. We describe the QVNS circuit design and operation, including the lumped-array Josephson-junction circuit and the unipolar bias technique. In particular, we describe the primary design considerations that determine the voltage accuracy of the harmonic tones.IEEE Transactions on Applied Superconductivity 07/2011; 21(3-21):681 - 686. DOI:10.1109/TASC.2010.2083616 · 1.24 Impact Factor