Ing. Radek Sedláček, Ph.D.

The summing integration (SumInt) analog to digital conversion (ADC) technique combines and preserve many of excellent features of double integration and sigma-delta ADCs. It is well suited for application where integral of continuously sensed input signal carries information to acquire. It has been initially conceived at the PiKRON company for digitizing compounds responses measured by UV-VIS spectrophotometric detectors in high-performance liquid chromatography systems. The compound concentration in the sample is proportional to the integral/area under response peak. In a contrast to double integration ADC, the SumInt ADC integrates input signal continuously and does not require reset/idle interval control. In comparison to sigma-delta ADC, the frequency of reference switching is much lower (less charge leakage). The paid price is sampling interval floating in a range of up to one half of the fixed modulator interval. The actual ESA funded De-Risk project focuses on reuse of the technique for low analog components count conversion in radiation tolerant systems where FPGAs are already in use.

Článek popisuje inovovaný systém pro porovnávání stupnice UTC(FEL) generované cesiovými hodinami 5071A/001 v. č. 3519 v Laboratoři přesného času a frekvence FEL ČVUT (Praha 6, Dejvice) a národní časové stupnice UTC(TP) udržované v Laboratoři státního etalonu času a frekvence (Praha 8, Kobylisy). Původní systém využíval pro porovnávání metodu společných pozorování (Common-View) pomocí GNSS přijímačů GTR 51/55 a současně dvoucestnou metodu přenosu času po optických vláknech pomocí optoelektronických adaptérů MATRIX. Nová metoda porovnávání je založena na technologii White Rabbit, která je v časových laboratořích FEL ČVUT, ÚFE AV a CESNET předmětem výzkumu od roku 2019.

This paper discusses the problems of the noninvasive diagnostic of high-voltage machines. The main role of the diagnostic is to predict an upcoming machine failure. Frequency response and frequency domain spectroscopy methods are studied in this paper. The methods are compared in terms of common instrumentation features. A development of a hardware platform intended for both methods is presented. The platform is evaluated in the terms of accuracy and compared with laboratory instrumentation. The results of the evaluation showed the proposed solution is able to implement both methods and have a measurement accuracy comparable with market available instruments implementing only one method

V čase rozšiřování využívání GNSS systémů v široké oblasti aplikací a to i v rámci strategické infrastruktury vyvstává potřeba systému detekujícího případné rušení tohoto signálu za účelem snížení provozuschopnosti dané infrastruktury. Příspěvek popisuje systém detektoru rušení GNSS signálu GIDeLoc (GNSS Interference Detector and Localizer), jeho funkce a složení. Současně popisuje proceduru zastaničení, která slouží pro inicializaci systému před jeho nasazením, způsob synchronizace mezi jednotlivými měřicími stanovišti a postupy výpočtů relevantních k požadovaným výstupům ze systému.

A national traceability chain from dc quantum Hall resistance (QHR) to capacitance has been established at Korea Research Institute of Standards and Science using various impedance standards and coaxial bridges. An ac-dc calculable resistance standard of nominal value of 12.9 k Omega was used as a transfer standard from dc to ac at the frequency of 1.541 kHz. Two ac coaxial bridges, developed by INRiM, were employed: a ratio bridge, linking the 103-k Omega ac resistor to the 12.9-k Omega ac-dc calculable resistor calibrated in terms of the dc QHR and a quadrature bridge, calibrating the 1000 pF capacitors versus the 103-k Omega ac resistors. The ratio bridge defines the 103-k Omega resistor as a two-terminal-pair (2TP) standard and the 12.9-k Omega resistor as a four-terminal-pair standard; a cable correction was applied to the 2TP defined standard. The stability of all standards has been monitored for more than 3 years to be within a few parts in 10(6). The capacitance value, obtained with the new traceability chain, shows an agreement (a few parts in 10(7)) in a comparison with the reference values, traced from the National Institute for Standards and Technology (USA).

This paper deals with a comparison between digital and analog implementation of a synchronous detection algorithm. The commonly used implementation methods of synchronous detection are stated within the paper. The paper describes FPGA-based digital and analog hardware approaches, focusing on the digital design. The characterizations of the used analog-to-digital converters are measured. A direct comparison between both proposed approaches in terms of sensitivity along with long-term stability is described. The results achieved, along with identified limitations and proposed improvements are widely discussed.

V čase stálého rozšiřování využívání GNSS systémů v široké oblasti aplikací, a to i v rámci strategické infrastruktury vyvstává potřeba systému detekujícího případné rušení GNSS signálu ohrožující provozuschopnost dané infrastruktury. Tento příspěvek popisuje systém, který je schopen odhalovat takovéto rušení typu „jamming“ a „spoofing“. Systém poskytuje uživateli informaci o spolehlivosti a integritě GNSS signálu a lokalizaci zdroje rušení. Zamezí tak případným nehodám či hrozbám vedoucím ke snížení bezpečnosti provozu infrastruktury, která využívá informace o poloze a času získané z GNSS.

A national traceability chain from dc quantum Hall resistance (QHR) to capacitance has been established at KRISS using various impedance standards and ac coaxial bridges. Two bridges developed by INRiM, were employed: a quadrature bridge, calibrating 1000 pF capacitors versus 103 k Omega ac resistors and a ratio bridge, linking the ac resistor values to an ac-dc calculable resistor calibrated in terms of the dc QHR. The capacitance value obtained with the new traceability chain showed an agreement (a few parts in 10(7)) in a comparison with the scale maintained at National Institute for Standards and Technology (NIST, USA).

This paper describes a development of a hardware platform suitable for the frequency domain spectroscopy (FDS) and frequency response analysis (FRA) applied for high-voltage machines diagnostics. The principle of the FDS and FRA methods widely used by maintenance technicians are briefly reminded. Important technical requirements for the instruments utilizing these methods are stated. A design of a hardware platform with parameters fitting both of the method and engagement of the latest electronics components is discussed. In order to verification of the design platform, a basic implementation of a vector voltmeter is described. Long term stability, phase shift sensitivity, and accuracy of the platform are evaluated.

This paper describes a developing of an analog to digital front-end suitable for the frequency domain spectroscopy (FDS) of high-voltage machines. The principle of the FDS is described and the requirements for the instruments utilizing this method are stated. The design of the front-end is described as a base of an FDS analyzer instrument. A basic implementation of the vector voltmeter is described. The implementation is verified in order to stability, a phase shift sensitivity and accuracy.

Measurement of the capacitance and the dissipation factor of the high-voltage machines insulation systems is one of several method used in the technical diagnostics. This paper deal with the development of instrument designed for measuring capacitance and dissipation factor of such machines. There is described principle of ratio measurement method as well as developer hardware based on FPGA application. Finally the measurement error analysis is given and its correction is presented.

This paper deals with the complex design of the partial discharge system for high-voltage machines diagnostics. The result of the work is complete measurement system, which fulfils specified functionality. Implementation relies on the FPGA with the advantage of system-on-the-chip technology. This solution enables flexible and powerful signal processing. Measurement principles and methods together with the test results are also mentioned.

This paper describes improved calculable 4TP coaxial capacitance standards with nominal values 10 pF and 100 pF. Modifications of construction and internal wiring made possible to lower and better define mutual inductions between some standard's parts than in previous version. Frequency dependencies of the standards were calculated up to 1 MHz and first measurements shown a good consistency between theoretical calculations and measurements. Achievable relative accuracy of measurements with such a type of capacitors seems to be on the level 10-5 in frequency range at least up to 1 MHz.

This paper describes a hardware design of a fully digital wideband PD meter based on application of FPGA as well as design of coupling device required for PD measurements. The designed coupling device has frequency bandwidth of 1 kHz - 10 MHz. The PD signal is digitalized by a fast 14-bit A/D convertor sampling at frequency of 50 MSa/s. The digital samples of PD signal are read by the FPGA, subsequently filtered by a number of digital FIR filter banks and stored in a 32 MB SDRAM memory. On request from PC software, the FPGA send samples in reduced form through Ethernet interface for the next signal processing and evaluation all important parameters of PD analysis. The paper also describes a design of smart charge calibrator especially developed for the PD meter testing and calibration.

This article focuses on the diagnostic system under development, which will enable to measure dissipation factor, energy and frequency of partial discharge occurrence. Based on measured results the related software will help to determine probable time between failures of power equipments. This procedure will result in significant economic savings in terms of inspections, repairs and shutdowns of equipments.

A four-terminal pair coaxial a.c. bridge was developed for calibrating both resistance and capacitance ratios and working in the frequency range from 100 kHz up to 1 MHz. Use of the same a.c. bridge with minimal changes for calibrating reference dividers and unknown impedances simplifies the whole calibration process. 1:1 and 10:1 ratio calibrations are performed with uncertainty of a few parts in 1e5. Bridge performance was checked on the basis of resistance ratio measurements and also capacitance ratio measurements.

Two bridge circuits for relating three-terminal or two-terminal pair impedance standards of any kind are described, balancing of which is made by voltages supplied from stable generators. In the first case two voltages are supplied, amplitude and phase of one of them being controllable. Four voltages are used in the second case and only their amplitudes are changed in the course of the balancing process. As a particular form of the second circuit, a coaxial quadrature bridge for relating resistance and capacitance standards has been realized and tested.

This paper describes a design of two-channel digital compensation unit which has been developed for accuracy measurement of four-terminal-pair (4TP) impedance standards by the three-voltmeter method. The FPGA based compensation unit senses a residual voltage on the low potential port of the compared impedances continuously. The sensing process is made by means of a synchronous detection technique; a principle of the lock-in amplifiers is implemented on the FPGA. Simultaneously a voltage proportional to the residual voltage is injected into a main measuring circuit via an injection transformer. Thanks to this feedback, residual voltages at low potential port of measured impedances are reduced more than 1000 times. A typical level of residual voltages is about 5 uV. The compensation unit operates in the frequency range from 10 kHz up to 2 MHz. The unit is controlled by a PC via optical insulated USB port.

A new series-parallel capacitance device for calibration of high-frequency inductive voltage dividers is described, which makes calibrations of ratios N:1, N = 1, …, 10 at a frequency of 1 MHz with uncertainties of less than one thousandth of a percent possible.

Two versions of four terminal-pair resistance standards have been made from surface mount resistors. Frequency characteristics of these standards, as well as frequency characteristics of a set of quadrifilar resistors with calculable frequency performance, have been measured by means of an Agilent 4285A precision LCR meter.

Two bridges for calibrating four-terminal-pair standards of self-inductance in the frequency range from 500 Hz to 10 kHz are described. The first is a multifrequency double-balance bridge for linking inductance to capacitance, the second one being a modified Maxwell-Wien bridge, in which inductive voltage dividers in conjunction with fixed resistance and capacitance standards serve as balance controls.

Four terminal-pair coaxial capacitance standards with nominal values of 1 pF and 10 pF have been realized, thin cylindrical electrodes of which are formed by copper foils glued on insulating supports. Parasitic inductances of both standards have been calculated and contribution of these inductances to frequency dependences of the standards has been evaluated. The values of the 1 pF and the 10 pF standard change by 0.04 % and -0.05% respectively when frequency changes from 1 kHz to 1 MHz.

Quadrifilar resistors with nominal values of 100 Ω, 1000 Ω and 10000 Ω, as well as a 100 Ω coaxial resistor, have been realized and their frequency dependences have been calculated from their constructional parameters. With the aim of experimentally verifying correctness of mathematical models used in these calculations, frequency dependences of ratios of parallel equivalent resistances of the realized resistors have been measured by means of a four terminal-pair transformer bridge.

A new technique for impedance measurement at frequencies around 1 MHz has been developed. The proposed method is based on the general principle of coaxial transformer bridges for impedance comparison. Two bridge arms are formed by the impedance standards to be compared, the other pair of arms by two voltages produced by a specially developed two-channel DDS generator. Amplitude resolution of 14 bits per channel and possibility of setting mutual-phase shift by steps of 3.8 x 10-4 rad make it possible to measure voltage ratios with uncertainties less than 1 part in 104. The method has been tested by measuring ratio of capacitances of two air capacitors having 1 pF and 10 pF nominal values. The difference of the actual and the measured ratio was less than 45 ppm.

A new construction of permuting capacitors device (PCD) for calibrating 10:1 high-frequency IVDs is described. SMD reed contacts are used for PCD capacitors switching. By means of a method based on the PCD and on voltage injection, calibration uncertainties better than 20 ppm (k=2) were achieved.

A new construction of permuting capacitors device (PCD) for calibrating 10:1 high-frequency IVDs is described. SMD reed contacts are used for PCD capacitors switching. By means of a method based on the PCD and on voltage injection, calibration uncertainties better than 20 ppm (k=2) were achieved.

Three versions of inductively coupled ratio arms have been prepared in the form of two-stage inductive voltage dividers. In a frequency range up to 1 MHz ratio errors of these dividers have been measured by comparison with a reference divider composed of eleven cyclically permuted capacitors.

A Maxwell-Wien bridge with a non-classical structure has been developed. The bridge allows a four terminal-pair measurement of inductance standards in the frequency range 500 Hz up to 10 kHz. The matter of bridge modifications concerns an application of inductive voltage dividers (IVD's) and precision electronic circuits, behaving as precise voltage followers. The designed voltage followers have been tested and the results of inductance measurements are corrected on their amplitude and phase errors. The preliminary results show that relative uncertainty (k=2) of inductance measurement (nominal value of 100 mH at frequency 1 kHz) is less than 50 parts in 1000000.

As the final stage of development of a new system for impedance calibrations, a facility for calibrating standards of mutual inductance has been realized. Being based on the threevoltmeter method, this facility makes it possible to calibrate 1 mH to 100 mH standards at frequencies up to 5 kHz with uncertainties of the order of 0.01 %. An improved direct connection technique is used when routine calibrations of mutual inductors are made by means of a four terminal - pair LCR meter.

A two-channel compensation unit based on an application of a digital signal processor is decribed. This special device, having implemented the algorithm of the synchronous filtering, is used for the compensations of spurious voltages in the measurement set-up of three voltmeter method. The unit works in frequency range 500 Hz - 5 kHz. If the compensation unit is applied into system, it is attainted the level of residual spurious voltages about a few of mikroVs. Thanks to this fact, the calibration of inductance standard in range 1 mH - 100 mH can be made with the uncertainty less than 100 ppm.

A two-channel compensation unit based on an application of a digital signal processor is decribed. This special device, having implemented the algorithm of the synchronous filtering, is used for the compensations of spurious voltages in the measurement set-up of three voltmeter method. The unit works in frequency range 500 Hz - 5 kHz. If the compensation unit is applied into system, it is attainted the level of residual spurious voltages about a few of mikroVs. Thanks to this fact, the calibration of inductance standard in range 1 mH - 100 mH can be made with the uncertainty less than 100 ppm.