NPL transforms Metrosol's temperature measurement capabilities, accelerating progress, and expanding their commercial opportunities.
The need
Metrosol Ltd, a leading instrument design company for temperature metrology, approached NPL to support them in their development of a novel a Johnson Noise Thermometer for use in harsh industrial environments. The absence of proven traceable methods to quantum standards has hindered temperature measurement assurance, posing a significant challenge.
Traditional thermometers, like thermocouples and platinum resistance thermometers, measure temperature indirectly using material properties and are therefore prone to calibration drift due to changes in the property they measure. Primary thermometers, like Johnson Noise Thermometers on the other hand, are immune to drift because their measurements are based on a fundamental physical law, meaning they can detect a true thermodynamic temperature, making them ideal in harsh conditions. Their measurement capabilities make them perfect for long-term measurements in nuclear environments, aerospace, and general metrology where stability is vital.
The solution
The Measurement for Quantum (M4Q) collaboration aimed to investigate how to achieve traceability to SI quantum units using Quantum Electrical Metrology and Josephson voltage systems. The project involved the calibration of Metrosol's Thermal Voltage Converter, ADC linearity measurement, and DAC output comparisons with reference systems.
A key part of the M4Q was calibrating the Analog-to-Digital converter (ADC) linearity used to measure the Johnson noise. This objective was achieved by two methods: traditional calibration using AC-DC transfer and Quantum voltage calibration.
Traditional calibration was performed by in depth analysis of Metrosol's Thermal Voltage Converter. This work gives Metrosol mobile traceability for their electronics during production and into the future. The Thermal Voltage Converter can be used to calibrate the Metrosol ADC to ensure the results are correct but is limited to sine waves and is not as accurate as direct comparison with a quantum voltage source.
The Quantum calibration gives a more accurate approach by knowing the exact voltage values. For this method, NPL used a Programmable Josephson Junction Standard (PJVS) to generate triangular/sine waveforms to check the linearity of the Metrosol ADC (mADC). We synchronised our PJVS to the mADC and sampled the waveforms using the mADC. We determined the linearity of the mADC by analysing the sampled data. Initially through our analysis, we found a significant nonlinearity for negative voltages. A fault was found in the mADC which through testing with our PJVS was resolved. The ability to know exact voltage values was crucial in fault finding and adding confidence in the mADC at Metrosol.
The impact
The M4Q collaboration significantly advanced Metrosol's technology, proving the unique added value of industrial Johnson noise thermometers. Metrosol’s product development capabilities have been boosted, with their newly calibrated thermal converter allowing them to conduct in-house AC measurements. By providing Metrosol with guaranteed performance figures and traceability, the Measurement for Quantum Scheme has allowed Metrosol to back up commercial claims and instil market confidence in their product.