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.
Accurate radio-frequency microvoltages
The questionable accuracy of radio-frequency microvoltages has been of great concern to the radio field for many years. There is an urgent need for a simple, yet reliable, source of microvolts for measurements in general and for radio receiver sensitivity determinations in particular. Extremely simple devices, which seem to satisfy that need most adequately, were recently developed. They are sources of potential drop obtained across a known resistance through which known currents flow. These devices provide constant voltage sources of accurate microvolts over a range of 1 to 105 and wider, at all frequencies to 300 megacycles and higher. They are adaptable for balanced as well as for unbalanced sources. Their electrical constants are simply determined by using known direct voltages and currents. Basic principles, design features, and applications are discussed.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.