Josip Butorac

Realization of the kilogram by measuring at 100 kV with the voltage balance ETF

The possibilities for adapting the existing electrostatic device known as the voltage balance ETF-84, to work with a voltage of 100 kV and a weight of 1 kg, are considered. A few theoretical analyses, experiments, and computer simulations have been carried out to define the measurement procedure needed at the required level of uncertainty of 1 part in 10/sup 8/. These analyses identified which parts of the balance itself and of the high voltage electrode isolation have to be reconstructed, as well as how the associated high voltage resistor has to be designed for this purpose.

Voltage balance for replacing the kilogram

The paper gives a short description of the basic principle of work of the ETF Voltage Balances, as well as the measurement procedures enabling the absolute determination of the Volt. We review previous results, and estimate the expected uncertainties for further experiments using the so-called charge-method. We review the calibration of the standards used with the balance. We have successfully started a new series of measurements at the end of 1993, and expect to report on the results at the end of 1994. >

Volt balance realization of the volt at ETF in Zagreb

A volt balance having plate electrodes operating in a temperature-controlled atmosphere of dry nitrogen is described. The voltage is measured by a special procedure of substitution of a weight for the electrostatic force, with automatic control of the balance equilibrium. This, together with the application of very sensitive capacitive transducers for measuring the balance equilibrium and electrode displacements enables a weighing reproducibility of less than 0.1 ppm to be achieved. The earthed electrodes are suspended over the beam arms by means of two thin strips separated one from the other in such a way that optimal sensitivity to the existence of horizontal electrostatic forces is achieved. Through the remote adjustment of the horizontal position of the high-voltage (H-V) electrodes, and by measuring the displacement of the suspended and H-V electrodes, it is possible to eliminate horizontal electrostatic forces. The displacement of the H-V electrodes by 51 mm (corresponding to a capacitance change of 100 pF) enables highly precise capacitance and length measurements to be made. The third improved version of the Zagreb Faculty of Electrical Engineering (ETF) volt balances is now being completed. The mean result of six measurements obtained with two earlier balances indicates that the difference between the International System (SI) volt determined by the ETF volt balances and volt BI-76 is +7.1 ppm with a random one-standard-deviation (1σ) uncertainty of 0.4 ppm and a systematic 1σ uncertainty of 1.6 ppm.

Calibration of the standard resistors by means of the standard capacitors and precise digital voltmeters

The calibration is carried out by measuring the ratios of voltages on an auxiliary resistor, once as a result of the current flowing through the previously calibrated capacitance standard, and the other time as a result of the current through the resistance standard. Using these voltage ratios, obtained with DC and low frequency AC current, measured by the precise digital voltmeters, a resistance standard can be calibrated with the uncertainty of 0.2 ppm.

DVM input and leakage resistance analysis in the DVM-based resistance measurement systems

The digit voltmeter (DVM) input and leakage resistances have been analyzed in the DVM-based resistance measurement system using one or two DVMs. The results are given both theoretically and experimentally. Shunting errors due to DVM-input and leakage resistances were substantially reduced by using a proper measurement method. The method is being further investigated for measuring high-ohm standard resistors.

Progress in measurements with the ETF voltage balance

The results of two series of measurements with the ETF-84 voltage balance carried out in 1987 and 1988, using the classical method of weighting, were previously presented by the authors (1988) with the proviso that some systematic errors had not been accounted for. Detailed analyses of these errors are not in progress, as are numerous experiments to determine the possible corrections and to estimate their uncertainties. A method for measuring the capacitive current when moving the high-voltage electrodes with a constant speed is established. In this method, there is no need to measure the AC capacitance between the electrodes. >

The basis of Croatian electromagnetic metrology

Measuring equipment, standards, methods and procedures necessary to ensure the traceability in the laboratory calibration system of electromagnetic quantities, are described. The accuracy scale and appropriate uncertainties appearing at the specific levels when measuring electric quantities such as voltage, current, power, resistance, capacitance etc., are analyzed. The research directions and possibilities of the international and national interlaboratory connections, are discussed.

Measurement of electrode surface effects in air capacitors using a precise Coulombmeter

A method by which air capacitor electrodes are charged with a DC voltage and then quickly discharged is described. Immediately afterwards, a very sensitive Coulombmeter is switched on to measure the additional discharging of thin dielectric films on the electrodes. The method makes possible the measurement of effects having a time constant of several milliseconds to several thousand seconds, and also enables the frequency dependence of the capacitance to be determined, even for time constants below 1 ms. >

Improved frequency measurement by means of DMM and verification of its specifications

A simple, but highly accurate, sampling method for the measurement of frequency by means of a digital multimeter (DMM) or a digital voltmeter (DVM) is explained both theoretically and from the applicative point of view. The mathematical background is given in short form, and comparison with other solutions is provided. High accuracy and behavior regarding random errors are foreseen by computer simulation and then proved in real laboratory measurements. Finally, verification of factory time-base specifications of sophisticated equipment is shown taking an HP 3458A DMM as an example device under test.

Use of precise digital voltmeters for ac voltage measurements

The possibility of using high-resolution digital voltmeters for ac voltage measurements at a frequency of about 16 Hz is presented. The method for the determination of correction factors in phase difference measurements with two synchronised voltmeters is described, and a level of uncertainty of 0,1 /spl mu/rad is achieved.