Improved Electrothermal Simulation for Low-Frequency Characterization of a Single-Junction Thermal Converter

We perform a numerical simulation for the low-frequency characterization of a single-junction thermal converter down to 1 Hz using an improved electrothermal model. The low-frequency characterization of a thermal converter below 10 Hz is of great importance for linking ac-dc transfer standards and low-frequency ac voltage standards based on sampling methods. One feature of our model is the incorporation of the heat capacity for the thermocouple, which has previously been neglected to reproduce an accurate thermal time constant. Our model also includes the temperature dependence of the Seebeck coefficient in the thermocouple in addition to the temperature-dependent material parameters of the heater. To verify the simulation results, the calculated results are compared with the experimental results, which shows that our improved model well reproduces the measured data below 1 Hz. The estimated uncertainty of the simulated ac-dc transfer differences is 49 μV/V at 4 Hz. These results suggest that our model is a useful predictive tool at low frequencies.