Yakup Gülmez

Four-terminal-pair capacitance characterization at frequencies up to 30 MHz using resonance frequencies

A new approach is proposed for the characterization of Agilent 16380A-type four-terminal-pair (4TP) air dielectric capacitance standards, which in the present study ranged from 1 pF to 1000 pF up to 30 MHz. The main objective is to determine all residual parameters of the four-terminal-pair capacitor (C4TP) defined in previous investigations. The key feature of this study is to find all resonance frequencies of C4TP up to 500 MHz using 4TP impedance and admittance values calculated from scattering parameter measurements employing a vector network analyzer. Inductive residual parameters of C4TP are calculated from these resonance frequencies, and capacitive residual parameters are measured by using a 1 kHz capacitance bridge.

A new design for calculable resistor

UME has improved a coaxial and bifilar type of resistors that have been widely used for determining of the resistance unit from DC to up to several kHz at many primary laboratories. This paper describes the modeling, construction and measurement results of the calculable resistors, which are specially designed in order to eliminate the effects of vibration and mechanical shocks during transportation, at a nominal value of 1 k/spl Omega/, 10 k/spl Omega/ and 12,906 k/spl Omega/.

A microwave system for humidity measurements

A microwave humidity measurement system based on microwave resonance has been developed at TÜBİTAK UME (National Metrology Institute of Turkey). This technique is based on microwave resonance frequency detection of a cavity that is sensitive to permittivity of air and water content. We have designed a copper microwave cavity resonator, a microwave electronics and a software to measure relative permittivity of air. Experimental results show good agreement with traditional humidity measurements in the range from 25% RH to 80% RH.

Intercomparison of a 10 mH inductance standard between UME-PTB

Turkish and German Metrology Institutes (UME and PTB) performed an intercomparison of 10 mH inductance standards at 1 kHz. The measurements of the thermostatically-controlled transfer standard of PTB were taken by new Maxwell-Wien bridge with a Wagner arm made in UME. Relative difference of UME and PTB measurements on the same standard was found to be 5.10/sup -6/. Results have shown that this type of Maxwell-Wien bridge is capable of producing very precise measurements on standard inductors and promised further developments that will increase the accuracy of the system.

Comparison of the input electrical power measurement methods for HIFU transducers

HIFU (High Intensity Focused Ultrasound) transducers are attractive tools for cancer therapy. They must be used carefully for operator and patient safety as they produce very high powers up to a few hundred watts, and characterized in many ways. The ultrasonic power of a transducer is directly proportional to the applied input electrical voltage, current and consequently electrical power. Internationally accepted methods for measurements of ultrasonic output power up to 10 W are well established in the IEC 61161 standards [1]. The same method was used for higher powers up to 150 W with an uncertainty of 4.7% for 1.1 MHz and 5.0% for 3.3 MHz in an intercomparison between national metrology institutes [8]. In this paper, input electrical power of the HIFU transducer, which is mainly converted into ultrasonic energy, was determined. 3 methods for the measurement of electrical power delivered to a reactive ultrasonic (HIFU) transducer were compared. Electrical power measurements were realized with an expanded uncertainty of 3.3 % for up to 50 W and 4.3 % for up to 100 W in the frequency range between 0.93 MHz and 3.1 MHz. Measurement devices were calibrated and verified by establishing traceability to electrical and ultrasonic standards at TÜBİTAK UME (The Scientific and Technological Research Council of Turkey, National Metrology Institute) primary laboratories. Electrical power measurement results obtained by this method were also compared with two different conventional power meters. Electrical power measurement results detailed in this paper showed an agreement with each other and conventional power meters.

S-parameter resonance method for the calibration of standard capacitors

National Metrology Institute of Turkey (TÜBİTAK UME) has developed a new approach for the characterization of Agilent 16380A-type four-terminal-pair (4TP) air dielectric capacitance standards in the range of 1 pF to 1000 pF up to 30 MHz. This method is based on determining all residual inductive parameters of 4TP standard air dielectric capacitors from resonance frequencies. These resonance frequencies were calculated using impedance and admittance values obtained from scattering parameter measurements up to 500 MHz employing a vector network analyzer. Capacitive residual parameters were measured by using a 1 kHz capacitance bridge.

Fabrication of 10 mΩ/10 A DC current shunt at UME

In this study, it is aimed to fabricate DC current shunt in the range from 1 A to 10 A with high accuracy and low drift. Resistance value of shunt was chosen as 10 mΩ which is compatible to the national traceability chain. 10 mΩ DC current shunt was fabricated, characterized and was put into use at TÜBİTAK UME (National Metrology Institute of Turkey) DC Resistance Laboratory.

An inductive voltage calibration system based on bootstrapping method

The need of calibrated inductive voltage dividers (IVD) with the smallest possible uncertainties was appeared for determination, maintenance and dissemination of the ohm and the farad in audio frequencies. In this paper an IVD calibration system that is based on bootstrapping method is described and the preliminary results and improvement efforts are mentioned. The relative uncertainty of the system from the preliminary results is 2.10/sup -8/ for the inphase component, 5.10/sup -8/ for the quadrate component at 1 kHz.