Tadeusz Skubis

A bridge for maintenance of inductance standard

A bridge for maintenance of primary 10 mH inductance standard is described. The bridge simplifies and speeds up the maintenance procedure of group inductance standard and enables also the calibration of an external standard in relation to any member of the group. It can measure directly the inductance and series resistance differences of compared inductors at frequency 1 kHz and at operating current less than 70 mA. The measurement range is within /spl plusmn/10 /spl mu/H and /spl plusmn/200 m/spl Omega/ of the nominal value, the resolution /spl plusmn/1 nH and /spl plusmn/20 /spl mu//spl Omega/, and type A standard uncertainties are smaller than /spl plusmn/2 nH, and /spl plusmn/1 m/spl Omega/, respectively. The inductance measurement uncertainty is approximately 20 times smaller than observed one-year drift of a single standard inductor. The bridge is provided with a serial PC interface, and a manual switch for fast choice of compared inductors. The paper presents the concept of the circuit and measurement procedure, enhancing the result accuracy. The influence of connecting cables and problems with switching of compared inductors are also discussed.

Vector Voltmeter for High-Precision Unbalanced Comparator Bridge

A new inductance comparator bridge has been constructed at the Institute of Measurements, Electronics, and Automatic Control (Gliwice, Poland) for the calibration of inductance standards in the frequency range of 100 Hz-10 kHz. Since the instrument belongs to the class of unbalanced transformer bridges, very accurate measurement of the voltage on the diagonal of the bridge is required. A vector voltmeter which enables the precise measurement of both components of the unbalance voltage is described in this paper. We report on the realization and characterization of the voltmeter which is an integral part of the new inductance comparator bridge.

Coherence of Comparison Results for 10 mH Inductance Standards

In the paper the method of checking coherence of comparison results for 10 mH inductance standards is presented. Formulas which determine level of coherence of comparison results for standard inductors are derived. Results for measurements of level of coherence for 10 mH inductance standards are presented and discussed. Coherence tests of comparison results are very good way to check comparators and help constructors of measuring equipment to improve designed instruments.

Thermal converter with quartz crystal temperature sensor for ac-dc transfer

The design and features of an experimental thermal ac-dc converter with frequency output are presented. A bulk acoustic wave LC-cut quartz resonator with linear frequency versus temperature characteristic is used as a temperature sensor. The resonator is excited through an inductively-coupled Butler oscillator. The sensitivity of this device is about 1 kHz/spl middot/K/sup -1/. In order to reduce the electromechanical coupling between the heater and the vibrating area, a thin-film Ni-Cr heater was sputtered at a location where the convex surface of the resonator intersects the nodal plane of the vibrations. The overall temperature coefficient of the output frequency is about -0.3%/spl times/K/sup -1/. The responsivity of the device is 300 kHz/spl times/W/sup -1/. The short-term stability of the output frequency permits an ac-dc transfer at the 10/sup -6/ level. The ac-dc voltage transfer difference of the converter is less than 10/spl times/10/sup -6/ at an input voltage of 3 V in the frequency range from (1-5) kHz. Below 1 kHz, the ac-dc transfer difference increases proportionally to the input power and doubles with a decade decrease of the input frequency. No resonances of the quartz plate were detected between 5 kHz and the frequency of the strongest fundamental thickness shear mode (9.5 MHz). Hence the converter can be probably used up to 1 MHz.

Undirected response transducer of magnetic field induction

This paper present the concept of the transducer for shape reconstruction and magnetic induction measurement of periodic arbitrary shape wave magnetic field. The measuring head consists of three coils with separated leads. Coils are fixed perpendicularly one to the other. Coil output voltages are synchronously sampled and the input samples are processed according to the algorithm developed. The characteristic curve of the transducer is theoretically deduced. Algorithm fixing signs of currently reproduced output samples of reconstructed shape wave is commented. Most significant uncertainty sources of the circuit thrust by essential blocks of signal processing path are analyzed. It was confirmed by simulation that the reconstructed wave shape and calculated induction value are independent of angle setting of measuring head in magnetic field. The transducer sensitivity to the angle setting in the magnetic field is very small.

Improved design of inductive voltage divider winding

The paper presents a parameter improvement method of the multifilar winding, commonly used in inductive voltage dividers. The method allows one to determine an optimal section connection sequence in multifilar bundle of wires forming the multisectional winding. The procedure of measurement of capacitances between pairs of individual sections and capacitances between individual section and its shield is presented. These capacitances are arguments of an optimizing function. Examples of calculations show that the inherent scatter of the multifilar winding capacitance can be used for winding parameter improvement. By using this method it is possible to lower the input capacitance of the winding as well as the correcting capacitors values by up to 2.5 times.

Calibration and Leakage Impedance Measurements of a Standard 1:2 Ratio Autotransformer Inductive Voltage Divider

A method and circuit for determination of the ratio error of an inductive autotransformer voltage divider having a 1:2 nominal ratio are shown in this paper. The circuit is used for measurement of a differential voltage between corresponding taps of the divider investigated and reference inductive divider based on which ratio error is determined. The distinguishing feature of the measuring method developed is the possibility of virtual reconstruction of the rated ratio value of a standard divider. Thus, during the measurement process, there is no need to use the standard divider; instead, a divider having the constant, unknown error is used. The proposed circuit can also measure the leakage impedance of divider windings when using the developed three-stage procedure of measurement. In this paper, the obtained measurement results of the ratio errors and winding leakage impedance for different divider load and in a wide frequency range are presented.

The Use of 1:1 Comparator Bridge for 10:1 and 1:10 Inductance Standard Transfer

An idea of using 1:1 high-precision comparator bridge for 10:1 and 1:10 impedance transfer is described in this paper. The procedure described in this paper was applied to transfer the unit of inductance from 10 to 1 mH, and from the 1 mH to the 100-\(\mu \) H standard inductor. A symmetric summing branch-joint was designed especially for adding in a series up to three GenRad-type standard inductors, and thereby enables the transfer. Uncertainty analysis and results of measurements performed for 10:1 transfer of inductance are presented. The analysis and the results achieved prove that using 1:1 impedance comparator bridge and applying proposed procedure is possible to transfer the unit to the objects of 10 times smaller values with relative standard uncertainty only a dozen percent higher than relative uncertainty estimated for 1:1 comparison of the standards having nominal values as the wanted standard. The idea presented here for inductance comparison is universal and can also be applied for other kinds of standards compared in National Metrology Institutes.

The directionless instrument for the periodical magnetic field analysis

The instrument for magnetic induction measurement is described. The instrument sensitivity depended on the field direction is significantly reduced. The instrument can recover the curve of induction B (for pulsating field) or induction modulus for rotating field in the real lime. Signal processing in the measuring chain is showed. A uncertainty of measuring process is estimated. Sources of most errors and uncertainties of the measuring path are pointed out. Special attention is paid into errors born in measuring head. Results of laboratory tests are compared with standard instrument ones. Application of the prototype is verified. The instrument presented offers wide possibilities of magnetic field measurement and can be treated as an optional to the solution based on Hall instruments, having some drawbacks in individual situations, e.g. at high temperatures.

Ambient temperature coefficient of thermal piezoacoustic sensors operating in a twin configuration

This paper is focused on the ambient temperature coefficient of the output frequency of thermal piezoacoustic sensors operating in a twin configuration (differential mode). The sources of the ambient temperature coefficient of the sensor are pointed out and the partial temperature coefficients of each block of the measurement chain are analysed with special attention to the influence of the non-linearity and mismatch of the frequency-temperature characteristics of the active and reference sensor. The derived equations are verified experimentally using the model of a thermal r.m.s. converter. A method for the reduction of the ambient temperature coefficient based on the proper choice of resonance frequency of the reference sensor is proposed. The presented analysis is valid for small variations of the ambient temperature, within the range of a few degrees Kelvin.