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; · 1.90 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; · 1.20 Impact Factor
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ABSTRACT: The National Institute of Standards and Technology has developed a quantum-voltage-noise-source-calibrated Johnson noise thermometer (JNT) to provide a new electronic measurement technique for determining the Boltzmann constant. Improvements in electronics and synthesized noise waveforms have led to reduced uncertainty in the measurement. Recent investigations have shown that some of the distortion in the present electronics arises in the differential stage of both the preamplifier and the analog-to-digital converter (ADC). The distortion can be reduced by compensating the direct current offset of the signal at the inputs to the differential stage. A four-channel cross correlation JNT with optimized preamplifiers and new ADCs is being assembled. The improvements are on track to reach the goal of an electronic measurement of the Boltzmann constant at a relative uncertainty of 6 × 10<sup>-6</sup>.IEEE Transactions on Instrumentation and Measurement 08/2011; · 1.36 Impact Factor