Low voltage AC-DC transfer standards at LNE
This paper describes the method used to establish the traceability of LNE AC-DC transfer standards in the mV-range to the 1 V multijunction converter, which serves as the primary AC-DC standard. Main uncertainty components are listed and final uncertainty given for the different voltage levels. An independent method was developed for the calibration of thermal converters at 0.3 V and 0.2 V. The agreement between this method and the step-down is within the standard uncertainty.
Recharacterization of thermal voltage converters after thermoelement replacement
This paper describes the relationship between the characteristics of various thermoelements (TE's) as voltage or ourrent converters and the overall ac-dc differences of a voltage range. An algorithm is presented to predict the ac-dc differences of series resistors with different TE's, and a method for recharacterizing a thermal voltage converter containing a replacement TE is given. The measured results show that for most applications, a complete recharacterization of the TVC set is unnecessary.
Evaluation of AC-DC Transfer Errors for Thermal Converter-Multiplier Combinations
In the build-up calibration of precise coaxial ac-dc thermal voltage converters, separate thermal converter and multiplier modules are combined and intercompared. For routine calibration or testing to specification, ac-dc transfer errors associated with the thermal converter modules can usually be neglected. However, for the calibration of standards to the highest accuracy, where the uncertainty may be < 5 ppm at frequencies in the range 25 Hz to 100 kHz, thermal converter errors must be included. An expression is derived for ac-dc transfer error in a thermal converter-multiplier combination. Multiplier transfer error is subject to loading effects by the thermal converter module, and the sensitivity of multiplier transfer error to changes in converter loading is assessed. Experimental results are presented to demonstrate the contribution of thermal converter voltage and current transfer errors to the error of the combination.