In this paper, improved sine-fitting algorithms for the measurement of amplitude and ph ase difference between two records of digitized sine waves with the same frequency are presented. These algorithms can be used for example in impedance measurements or to accurately measure the input and the output of a linear system to be characterized in the frequency domain both in amplitude and in phase.

A study of the resonance characteristics of low frequency ultrasonic transducers is presented in this work. The effect of the influence of the equivalent output resistance of the driving circuits on the shape of the frequency response and the sensitivity of the transducer is investigated. Theoretical presentation is accompanied by simulation analysis and verifying experimental measurements.

Performances of ΔΣ modulators are evaluated by applying a coherently sampled tone and by estimating powers of the in-band tones and noise. In particular, the power of the shaped noise is usually estimated by subtracting the evaluated input tone from the output data and by integrating the power spectral density estimated by means of the periodogram. Although the coherency, the finite number of processed samples induces spectral leaking of the wide. band noise, thus affecting the noise power estimate. To cope with such an issue, usually data are weighted by the Hanning sequence. In this paper, the noise power estimation error induced by the use of such window is investigated, and a criterion for choosing the minimum number of samples N which bounds the relative leakage error within a specified maximum value is explicitly given. Moreover, it is shown that, for an N, such an error is negligible for modulator orders lower than 3. Higher order modulators require the use of a large number of samples to bound the relative error of the noise power estimate when high oversampling ratios are employed.

A method for the assessment of the dynamic behaviour of heavy current shunts is described, which is based on the evaluation of the shunt frequency response through spectral analysis of input and output measured signals. The method has been tested by applying it to simulated current impulses and experimented in the case of a pulse current, generated by the discharge of a cable capacitance, measured by a thin walled coaxial-tube shunt.

Time Domain Spectral Analysis is presented in this paper as a new, original approach to the analysis of signal spectrum (having samples of the measured signal). The uniqueness of this method is in avoiding of any kind of Fourier transform, which showed to be of limited accuracy when the samples' errors (measurement imperfections) are taken into account, even applying windows and various approximations. The majority of calculations are based on our previously developed method for high accuracy measurement of a single sine wave. The basic idea of this method is to extract all time domain samples of a particular wave from samples of the whole signal, and then to calculate parameters of that component by applying the method for measurement of a single sine wave. This approach has been tested with extended and rigorous computer simulations (explained further in the text) and partially in real laboratory measurements. It is demonstrated that estimated accuracy of parameters of the fundamental wave is about 4 ppm, even though the samples' errors are of the order of 20 ppm. The estimated accuracy of the higher harmonics is better than 500 ppm (regardless of their number, and the same for amplitude and phase).