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.
An Automatic System for AC/DC Calibration
An automatic ac/dc difference calibration system using direct measurement of thermoelement EMFs is described. The system operates over a frequency range from 20 Hz to 100 kHz, covering the voltage range from 0.5 V to 1 kV. For all voltages, the total uncertainty (including the uncertainty of the specific reference thermal converters used) is 50 ppm at frequencies from 20 Hz to 20 kHz, inclusive, and 100 ppm at higher frequencies up to 100 kHz. In addition to ac/dc difference testing, the system can be used to measure some important characteristics of thermoelements, as well as to calibrate ac voltage calibrators and precision voltmeters. Results of intercomparisons between the new system and the manual NBS calibration system, using single-range, coaxial-type, thermal voltage converters as transfer standards, are reported. The results indicate that the ac/dc differences measured are accurate to well within the combined total uncertainty limits of the two systems.
The costs of identifying undiagnosed prostate cancer in asymptomatic men in New Zealand general practice
Background. Screening for prostate cancer (PCa) using the prostate-specific antigen (PSA) test is widespread in New Zealand. 3 informed testing history in 2007–09 were NZ$8887 compared to NZ$13 870 if the men had PSA tests in 2007–09. If we assumed a PSA test involved a full 15-minute general practice consultation, the estimated costs increased to NZ$26 877 per PCa identified. Conclusions. Screening of asymptomatic men for PCa is widely practiced. Most of the costs of screening were incurred in general practice. Calls for men to receive increased information on the harms and benefits of screening will substantially increase the costs. The current costs could be reduced by better targeting of screening.