The aim of this paper is to estimate the limitations of parametric faults testing in analog circuits result from fault-driven instability. The linear fractional transformation (LFT) and structured singular value (SSV), the analysis methods from robust control theory, are employed to investigate which parameter could lead to instability of a circuit under test (CUT), and to quantify the deviation in component parameter value that will cause instability. The leapfrog filter is studied as CUT. The SSV based analysis procedure is applied to a Simulink model, which is realized as LFT representation of faulty circuit. Numerical results show that leapfrog filter is highly susceptible to lose stability due to faulty RC elements.

This paper describes the procedures developed in the Laboratory for Ship and Marine Hydrodynamics (LSMH) of NTUA to test large models of ships at sea. It is common practice in experimental ship hydrodynamics to test scaled ship models in Towing Tank facilities, to investigate their performance in calm water and in waves. However, it is both time-consuming and very expensive to generate conditions, which simulate properly the actual sea environment. Parameters of the environment such as the incident wave angle, the short-crested nature of the waves encountered in real world, the effect of the wind and the scale of the experiment, which should be accommodated in the available facility, reduce, or even prohibit in some cases, the execution of such tests.
An alternative to laboratory measurements is to conduct tests with larger models at sea and to record both the sea conditions and the ship performance. This paper describes the design, specification, instrumentation and preparation of this kind of tests. Their advantages and shortcomings are also discussed.

The traceability chain of the Primary Electromagnetic Laboratory (PEL) is presented, and the place of the resistance standard of 100 MΩ is analysed in details, as well as its construction and characteristics. Its one hundred 1-MΩ elements in parallel connection forms the 10-kΩ value, and can be easily compared to the reference 10 kΩ standard of PEL; in that way its long-term drift was found to be ≈ 0,067 ppm/day (ppm means parts per million). Furthermore, the method of comparison of 100 MΩ resistance standard by means of 100 pF capacitance standard and high-resolution digital voltmeters (DVs) is analysed, where DVs measure ac voltage of frequency close to 16 Hz in dcv range, and the mean value of one-third cycle is measured. It was found that the voltage ratio could be stable within the limits of 0,1 ppm when the additional frequency stabilization of the ac calibrator is used.

At IEN, a guarded switching system for automatic selection of high value resistors under calibration was developed and metrologically characterized. By means of this system it is possible to select and connect to the measurement system high value resistors in three terminals configuration. As a matter of fact, its guard system allows to reduce the effects due to all the dispersion currents, due to insulation resistances between the resistors under calibration and their shields and due to the switching and connection system (such as insulation resistances among connections, of cables and connectors used for resistors connections). This system utilizes some details of the device described in [6, 7]. The uncertainties that can be reached with the measurement system in connection with the scanner in the calibration of high value resistors and a compatibility test of measurement performed with and without the scanner, are also given.

Partial Discharges calibrator principles and microprocessor controlled calibrator design are discussed. The calibrator charge generation technique is classic electrical with storing capacitor. The microprocessor control of the calibrator is perspective because of easy calibrator parameters modification and remote control.