Calibration of the dual-mode auto-calibrating resistance thermometer with few-parts-per-million uncertainty

Abstract

The dual-mode auto-calibrating resistance thermometer (DART) has recently been proposed for highly accurate temperature measurement based on noise thermometry. In this paper, it is demonstrated that calibration and operation of the DART at part-per-million (ppm) level should be possible with the hardware developed. For this purpose, we have extensively tested a representative signal path comprising the basic DART components. This includes a low-noise amplifier connected to a 24-bit Σ∆ ADC and a metrology-grade voltage reference. A Josephson arbitrary waveform synthesizer (JAWS) generates a pseudo-noise consisting of low-distortion multitones superimposed on a low-frequency square-wave reference voltage. Using this signal, a fast and efficient calibration scheme for the signal path gain is demonstrated. The reference voltage stabilizes the gain at ppm level. We observed gain fluctuations within ±2 µV V −1 over a period of 19 d, a temperature coefficient of −0.5 µV V −1 K −1 , and insignificant nonlinearity within an uncertainty band of ±2 µV V −1 for rms input levels between 5 µV and 80 µV. The behavior of the signal path with a 300 Ω resistor as a noise source was also investigated. From the observed stability of the voltage reference and flatness of the noise gain between 10 kHz and 225 kHz, we estimate that the presented hardware components are suitable for temperature measurements with systematic uncertainties well below 10 µK K −1 .

Practical realisation of the kelvin by Johnson noise thermometry

“…Another approach, which also exploits highly linear and stable electronics, is to simply to measure the noise power over a wide bandwidth, supported by occasional internal calibrations against a dc reference, and less frequent calibrations against a QVNS [99][100][101][102]. This method eliminates some of the concerns about non-linearities associated with the superposition method, at the expense of increased dependence on models of amplifier noise currents and voltages, and of the system frequency response.…”

Announcing the 2022 Measurement Science and Technology Outstanding Paper Awards

“…The paper [2] describes a unique high precision temperature measurement technique that enables measurement based on both resistance thermometry and Johnson noise thermometry (JNT) using a single sensing element, a standard platinum resistance thermometer (SPRT). SPRT is the interpolating instrument for a wide temperature range in the definition of the International Temperature Scale of 1990 (ITS-90), resistance thermometry being the highest precision temperature measurement method.…”