Abstract: A protective relay determines frequency of an AC signal of an electric power system. The protective relay includes a circuit measuring the AC signal period between zero crossings to provide a measured period value. A microprocessor includes a random access memory having a five-element array, which collects five consecutive values of the measured period values. A microprocessor routine chooses a median from the measured period values and generally determines the frequency based upon the median. The median is ignored and the previously determined line cycle period is adjusted to determine the new line cycle period if: an absolute value of a difference between a last value of the measured period values and a previously determined line cycle period is not less than a predetermined value; and the last value of the measured period values is within the limits of the array.

Abstract: The CPU outputs to the delay circuit 22 delay time setting signals for setting the delay time, based on input delay time data input from an external input device. The delay circuit 22 re-sets the delay time via new delay setting signals input from the CPU 24 and delays the trigger signals input from the trigger circuit 21 based on the specified delay time and outputs the resulting signals to the clock generator 23. The clock generator 23 outputs new sample start signals to the A/D sampler 3 at the input timing of the delayed trigger signals input from the delay circuit 22, thus changing the sampling start timing of interference signals in the A/D sampler.

Abstract: The present invention relates to a high speed sample and hold circuit having a plurality of sample and hold subcircuits coupled in parallel between an input and an output. The circuit also having a calibration sample and hold subcircuit coupled to the plurality of sample and hold subcircuits. The calibration circuit is operable to modify a timing for one or more of the plurality of sample and hold subcircuits to thereby reduce sampling mismatch between the plurality of sample and hold subcircuits. The present invention also having a method of reducing timing mismatch in a high speed, parallel coupled sample and hold circuit.

Abstract: A digital video signal monitoring apparatus comprises means (2,4,6) for receiving a digital video signal and extracting therefrom a plurality of digital signals, each of which comprises a plurality of successive digital sample values. The apparatus further comprises means (10) for interpolating additional digital values intermediate the successive samples of the or each extracted digital signal and means for displaying the waveform of the or each extracted digital signal as a series of discrete points corresponding to its respective digital sample values and interpolated digital values. Thus, none of the original signal information is lost in displaying a signal waveform having a substantially continuous appearance.

Abstract: A method and an apparatus for measuring the instantaneous frequency of FM modulated signals, includes sampling, instantaneous frequency computing, and lowpass filtering. FM modulated signal are sampled at prescribed intervals to provide digitized FM signal. The instantaneous frequency is computed by manipulating the digitized FM signal mathematically using a new mathematical equation proposed in this invention to provide the instantaneous frequency based on digitized FM signal samples. More accurate instantaneous frequency values can be obtained by filtering the computed instantaneous frequency values using a lowpass filter.

Abstract: A method and apparatus for spectral analysis of a sampled signal are provided. According to the method, a first time interval &Dgr;T is determined which represents a sample set over which the signal can be averaged for purpose of decomposing the signal into instantaneous mean and random components. From random component of the signal, the optimal time-dependent time interval AW over which the random component should be averaged to obtain the instantaneous frequency spectrum (IFS) is then calculated based upon the instantaneous signal memory. Signal memory specifies the extent in time beyond which the signal “forgets” its past behavior and thus is a measure of its degree-of-randomness. Defining AW in this way reduces the likelihood that short-lived events are lost (or masked) due to uncharacteristically short (or long) averaging intervals. Importantly, both time intervals &Dgr;T and AW are dynamic and vary randomly with time.

Abstract: A frequency synthesized signal generator outputs a frequency synthesized signal having a frequency equal to a repetition frequency of a signal under test by employing a reference signal. A phase comparator detects a phase difference between a phase of the frequency synthesized signal and a phase of the signal under test, and outputs a phase difference signal. A voltage control oscillator generates a reference signal phase-synchronized with the signal under test based on the phase difference signal output from the phase comparator, and feeds the reference signal back to the frequency synthesized signal generator. A sampling signal generator circuit generates a sampling signal applied to a sampling section by employing the reference signal output from the voltage control oscillator.