AC–DC Transfer and Verification of Ultra-Low Frequency Voltage From 0.1 to 10 Hz

A system for ac–dc voltage transfer at ultra-low frequencies is established with a dual-heater thermal voltage converter (DHTVC) in this article. The system is based on the premise that the thermoelectric potential of the thermal voltage converter (TVC) is square related to the input voltages. The output thermoelectric potential is constant when two orthogonal and equal-amplitude sinusoidal signals are input to the DHTVC. How to evaluate and compensate for the key parameters that affect the stability of output thermoelectric potential is discussed in detail. In this article, a verification method is also proposed to prove the accuracy of the ac–dc transfer results at low frequencies based on quantum voltage technology. The high-precision digitizer PXI-5922 is introduced as the transfer standard. The ac–dc difference of sampling error is calibrated using ac–dc voltage transfer with DHTVC as the reference standard at low frequencies down to 0.1 Hz. The dc and ultra-low frequency errors are also calibrated by programmable Josephson voltage standard (PJVS). The uncertainties of calibration results from two different methods are evaluated, respectively. The calibration results from ac–dc voltage transfer with DHTVC and PJVS show good agreement and inconsistency is less than 5
$\mu \text{V}$
/V at frequency ranges from 10 down to 0.1 Hz.