Current development status.

Measured results

Everything here comes from work we have published.

Measurement performance of 0.1 per cent in 5.3 seconds

0.1 % in 5.3 s

Extrapolating measured noise power to zero gives a temperature-axis intercept of −273.415 °C, against a true absolute zero of −273.15 °C

−273.415 °C

The intercept is more than five times closer to absolute zero than the proof-of-principle prototype managed under similar measurement parameters

−271.79 °C → −273.415 °C

Weighting the cross-correlation frequency bins by the inverse of their squared uncertainty reduced measurement uncertainty by 28 per cent

28 %

The proof-of-principle prototype weighed 35 kg and occupied 70 litres

35 kg · 70 L

The bespoke 24-bit converter replaced a commercial 16-bit instrument, cutting power from 45 W to 3.3 W and volume from 6,970 cm³ to 16 cm³

45 W → 3.3 W · 6,970 cm³ → 16 cm³

Tested for radiated RF immunity to EN 61000-4-3 at 10 V/m from 80 to 1000 MHz and 3 V/m from 1.0 to 2.7 GHz

10 V/m, 80–1000 MHz · 3 V/m, 1.0–2.7 GHz

The thermometer was unaffected by the applied fields, making it the first Johnson noise thermometer able to work in extreme electromagnetic environments to official standards

The sense resistance is typically 5 kΩ, where prior-art Johnson noise thermometers use around 100 Ω

5 kΩ

The measurement uses a bandwidth of 1.2 MHz

1.2 MHz

The thermometer works over the band 10 kHz to 1.2 MHz

10 kHz – 1.2 MHz

Standard deviation of 1.08 °C at 1,000 °C for the first high-temperature Johnson noise thermometer system

1.08 °C at 1,000 °C

At 1,000 °C a thermocouple shows less short-term scatter than the noise thermometer, at 0.47 °C against 1.08 °C

0.47 °C thermocouple · 1.08 °C JNT

Sensor resistance and Johnson noise are measured from the same block of data, so the resistance is measured rather than assumed

6.5536 s

Converter linearity measured by NPL against a Josephson voltage standard

Josephson-traceable

Programme targets, not results

These two are where the work is going. They are published as targets and are listed separately so they cannot be read as things already achieved.

The programme target is to bring the whole system under 1 kg and under 1 litre

<1 kg · <1 L

ThermoSI work package 2 is taking practical Johnson noise thermometry to 1,200 °C, with a target uncertainty below 3 °C

<3 °C at 1,200 °C

Measurements from Developments Towards an Industrial Johnson Noise Thermometer (2019) and Challenges and solutions in the development of a Johnson noise thermometer (2024). All of our papers are on the publications page.