Improved Measurement of AC–DC Transfer Difference Using a Low-Drift Single-Junction Thermal Converter

We reduced the exponentially decreasing thermal drift of a single-junction thermal converter and performed comparison measurements of the ac-dc transfer difference. The thermal converter was mounted on a metal block using a high-thermal-conductance paste; this treatment is crucial to improving the thermal drift. Numerical calculations using a thermal model that includes the temperature increase on the cold side of the thermocouple can explain the measured thermal drift. Our system, which uses a low-drift thermal converter, allows comparison measurements of the ac-dc transfer difference at a few parts in 10⁷ with a short measurement time if a sufficiently long waiting time is used.