Performance of Single Junction Thermal Voltage Converter (SJTVC) at 1 MHz via Equivalent Electrical Circuit Simulation
The physical structure of the SJTVC can be represented via simulation using an equivalent RLC circuit to investigate the performance and estimate the error sources when using this device as a precise tool for AC voltage and current measurements. This paper describes instruments and techniques that apply on 0.6 V thermal converters to achieve this target. The technique was performed, theoretically and practically, to investigate the frequency-dependence of the SJTVC up to 1 MHz. The LTspice/SwCAD III simulator was used to analyze the effect of the physical structure of SJTVC in an effort to better understand the origin of errors at 100 kHz and 1 MHz. The practical results were firstly measured at National Institute for Standard and Technology (NIST), US to validate the simulation model at 100 kHz. The model then used to estimate the AC-DC transfer error of the SJTVC at 1 MHz. Some of the dominated error sources such as the changes of the real part of the heater impedance, the effect of thermocouple grounding and the power consumed in the internal resistance of the thermocouple are estimated at 100 kHz and 1 MHz. The expanded uncertainty assigned to the AC-DC automated calibration system of NIS is also described.
A Step-Down Technique to Calibrate AC Current Down to 10 μA Using a Precision 10 mA Current Shunt
This paper describes a calibration procedure for AC current measurements at 1 mA, 100 µA and 10 μA using a NIST-calibrated 10 mA current shunt as a reference standard. The procedure involves a step-down technique using the reference transfer standards (RTS) as a precision current divider. The RTS is used at values of 370 Ω, 3.3 and 30 kΩ to provide the intended currents. Uncertainty calculations are estimated for calibrating the AC current of 10 mA, 1 mA, 100 μA and 10 μA at 55 Hz and 1 kHz. The expanded uncertainties are around the values of 37 nA and 1 nA for the ranges of 1 mA–10 μA respectively.
AC-DC Difference Calibrations
Abstract: This publication collects and summarizes the specialized information needed to operate the ac-dc difference laboratory and calibration service at NIST (Gaithersburg). It also serves as a convenient reference source for the users of this calibration service and other interested people by documenting the service and its underlying background in considerable detail. It contains the following: an annotated table of contents, a topical index, and a glossary of common ac-dc acronyms; an overview of the service; selected published papers; instructions for the operation of the comparator systems; a schedule for the recalibration and periodic checks of the NIST thermal converters; and a sample report of calibration.