Advanced thermal readout techniques for ac voltage metrology

One of the most accurate methods for quantifying ac voltage amplitude to compare the rms amplitude of an ac waveform to an equivalent dc voltage using a device called a multi-junction thermal converter (MJTC). The MJTC produces a dc output voltage in response to the temperature rise from Joule heating due to electrical power dissipation in a resistive heater. The uncertainty of an MJTC measurement is about 1 µV/V (1 ppm) for voltages in the range of 0.5 V to 10 V and frequencies in the range of 40 Hz to 20 kHz. Conventionally, the rise in temperature due to Joule heating is measured on the MJTC by an array of thermocouples. Although well-established, this type of readout suffers is made challenging by the relatively large resistance (~10kΩ) of the thermocouple array, and the low (several mV) thermovoltage. Here, we present our research into alternative measurement techniques based on physical phenomena such as infrared emission, superconductivity, and photonics in order to achieve improved stability and sensitivity and to extend the voltage and frequency range in which the measurement is accurate, bridging fundamental research with the engineering problems of harnessing useful physics to achieve advanced measurement technology.