Development of thin-film multi-junction thermal converters

The method that can derive an AC voltage standard with the highest precision is the AC-DC transfer method, in which a thermal AC-DC converter (thermal converter) is used to compare an AC voltage with a DC voltage standard. Therefore, AC-DC transfer standards have been supplied as national AC voltage standards. With respect to the provision of ACDC transfer standards, the AC-DC transfer differences of a thermal converter are calibrated, which correspond to the conversion error from a DC voltage to an AC voltage. In other words, AC standards are provided to calibration laboratories by calibrating their thermal converters. As explained below, however, the conventional thermal converters are designed in a way to achieve the highest possible precision, which causes inherent structural restrictions to make them hard to be handled owing to the vulnerability to overcurrents and impact. As a result, they have not come into widespread adoption among calibration laboratories or in the industrial community. The majority of calibration laboratories and the industrial community carry out calibrations of AC voltage standards by using standard AC voltmeters and AC generators, and therefore they fail to benefit from the biggest advantage of thermal converters, namely stability. Meanwhile the range of AC voltage standards provided by calibration laboratories to the industrial community in Japan has not been sufficient enough because it is difficult to expand the range of AC voltage standards when AC voltmeters or AC generators are used as reference.