ABSTRACT
Francis L. Hermach's paper launched the field of ac-dc thermal transfer metrology, which forms the basis for ac voltage and current measurement and calibration throughout the world. It laid the foundation for the techniques of ac-dc transfer and provided the first theoretical basis for the thermal transfer structures used in all national measurement institutes. AC voltages and currents in the frequency range from low audio to hundreds of megahertz are measured most accurately by comparison to dc standards using ac-dc thermal transfer instruments. AC-DC thermal transfer structures were first applied in the audio frequency range and later at radio frequencies for difference measurements of voltage, current, and power. At audio frequency, thermal and thermoelectric effects ultimately limit the measurement uncertainty in conventional room-temperature thermal converters. Heater powers as high as a few tens of milliwatts and temperature differences as high as 100 K are common in some thermal converters.
