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.
IMPROVEMENT AND CONFIRMATION OF A NEW AUTOMATIC SYSTEM FOR AC-DC CALIBRATION AT NIS, EGYPT
The recent Improvements in AC-DC transfer capabilities at National Institute for Standards (NIS), Egypt, include an automated AC-DC transfer comparator system with international confirmation of the results through bilateral intercomparison with NPL, England. The system can be used to measure additional characteristics of thermoelements and operates over a frequency range from 20 Hz to 100 kHz for a voltage level from 0.5 V to 1 kV. The results of bilateral intercomparison including the proficiency test of the new system are reported. The expanded uncertainty assigned to the NIS working standard is given and its components are briefly discussed. The results show that the agreement between the two laboratories is better than the expected uncertainties
AC-DC comparators for audio-frequency current and voltage measurements of high accuracy
This paper surveys recent developments in high-accuracy ac-dc comparators, the basic standards for ac current and voltage measurements at audio and higher frequencies. These instruments compare the unknown ac quantity with a dc reference. The ac-dc transfer characteristics of thermal converters, the most widely used comparators, can be evaluated to about 10 ppm at audio frequencies in national metrology laboratories. With recent developments even better accuracies, and greater convenience with automatic comparisons, are feasible.