It is noticed in the paper that scaling of digital measurement signals during computer processing increase their volume so that after using standard compression methods it is impossible to obtain the volume of the compressed original signal. A reverse scaling operation with reduction of numeric errors is proposed as the method preceding compression. The operation restores the original signal and, therefore, restore the original signal volume. The rule of encoding measurement results into a certain number of significant digits is ecalled. The binary version of this rule is presented and it is observed that its application improves signal compressibility.

The paper presents an analysis of a coder with adaptive difference quantization (ADQ) [1] for compression of measurement signals. Thanks to the adaptation of the compression algorithm parameters to the variability characteristics (i.e. to the dynamics) of the signals recorded, the compression ratio can be optimised. The results of the study on efficiency (compression ratio) of the discussed compression algorithm compared with known lossless algorithms are presented in the paper. The study was carried out taking into account the influence of dynamical properties of the measurement signals.

The paper deals with the accurate slip measurement of induction motors. The proposed procedure uses a non-invasive slip measurement scheme based on digital filtering and dynamic parameter estimation. The slip measurement is carried out without speed sensor and is deduced analyzing the magnetic field harmonics spectrum in proximity of the induction motor. First the emf induced waveform, taken from a searching coil, is filtered using algorithms based on the discrete Fourier transform. Then the stator frequency and rotor requency are obtained by comparing the filtered voltage with a mathematical model using an optimization procedure. The model's parameters are varied until an adequate match is obtained with the filtered voltage. Experimental results are presented to validate this method.

The shunt active power filters are used to attenuate the harmonic currents in power systems by injecting equal but opposite compensating currents. Successful control of the active filters requires an accurate current reference. In this paper the current reference determination based on predictive filtering structure is presented. Current reference is obtained by taking the difference of load current and its fundamental harmonic. For fundamental harmonic determination with no time delay a combination of digital predictive filter and low pass filter is used.

Characterization of measurement by uncertainty becomes a commonly accepted practice. Since in case of several sources of uncertainties which may even be correlated finding the resulting uncertainty according to the Guide to the Expression of Uncertainty in Measurements [1] is not an easy task, computer simulations are a suitable tool respecting the possible correlations of quantities influencing uncertainty. Analysis of DFT spectrum uncertainty was published elsewhere for coherent sampling. We compare correction factors and remaining uncertainties of two methods of the DFT spectrum analysis applicable for noncoherent sampling. Simulations are performed on power-line frequency with predefined harmonic components and noise and ideal quantizer with selectable resolution.