A measurement system for determining a phase and amplitude influence of a device under test, comprising a measurement instrument having a signal generator, a local oscillator, a first mixer and an analysis unit is disclosed. The signal generator is configured to generate a source signal with a predetermined source frequency and a source phase, and to forward the source signal to the device under test, wherein the source signal is altered by the device under test in at least one of amplitude and phase, such that a measurement signal is generated and forwarded to the first mixer. The local oscillator is configured to generate a local oscillator signal with a predetermined local oscillator frequency and a local oscillator phase, and to forward the local oscillator signal to the first mixer. The first mixer is configured to mix the measurement signal and the local oscillator signal, thereby generating a first mixer signal. The analysis unit is located downstream of the first mixer and is configured to analyze the first mixer signal or a processed version of the first mixer signal. The measurement instrument is configured to perform at least two measurements of the phase and amplitude influence of the device under test by analyzing the first mixer signal or the processed version of the first mixer signal, wherein at least one of the source phase and the local oscillator phase is altered between the at least two measurements.

Conventional frequency detection circuits have a disadvantage that the circuit scale increases as the frequency of a reception signal to be detected increases.

A frequency detection circuit includes: a first signal source for outputting a first clock signal; a second signal source for outputting a second clock signal having the same frequency as but a different phase from those of the first clock signal; a first sample hold circuit for undersampling a reception signal using the first clock signal; a second sample hold circuit for undersampling the reception signal using the second clock signal; and a frequency calculating circuit for calculating the frequency of the reception signal using a phase difference between output signals of the first sample hold circuit and the second sample hold circuit.

A method for estimating a property of a signal (1) sensed in an electrical system, comprises the steps of sensing the signal (1) and estimating a fundamental period of a fundamental of the signal (1) by comparing the sensed signal (1) with at least one threshold (2) to detect threshold crossings and estimating the fundamental period from the threshold crossings. The signal property is then estimated from the fundamental period and/or from the sensed signal (1) during an interval of a length of the fundamental period. An electronic device according to the invention comprises a micro controller and/or an analogue circuitry which performs the method for estimating a property of a signal. Preferably, the micro controller and/or analogue circuitry controls other parts of the electronic device depending on the results obtained by the method for estimating a property of a signal.

A method for estimating a property of a signal (1) sensed in an electrical system, comprises the steps of sensing the signal (1) and estimating a fundamental period of a fundamental of the signal (1) by comparing the sensed signal (1) with at least one threshold (2) to detect threshold crossings and estimating the fundamental period from the threshold crossings. The signal property is then estimated from the fundamental period and/or from the sensed signal (1) during an interval of a length of the fundamental period. An electronic device according to the invention comprises a micro controller and/or an analogue circuitry which performs the method for estimating a property of a signal. Preferably, the micro controller and/or analogue circuitry controls other parts of the electronic device depending on the results obtained by the method for estimating a property of a signal.

A physical quantity measurement apparatus includes a first resonator, a second oscillator, and an integrated circuit device. The integrated circuit device includes a first oscillation circuit that causes the first resonator to oscillate, and thus generate a first clock signal having a first clock frequency, a second oscillation circuit that causes the second oscillator to oscillate, and thus generate a second clock signal having a second clock frequency which is different from the first clock frequency, and a measurement unit that is provided with a time-to-digital conversion circuit which converts time into a digital value by using the first clock signal and the second clock signal.

A physical quantity measurement apparatus includes a first resonator, a second oscillator, and an integrated circuit device. The integrated circuit device includes a first oscillation circuit that causes the first resonator to oscillate, and thus generate a first clock signal having a first clock frequency, a second oscillation circuit that causes the second oscillator to oscillate, and thus generate a second clock signal having a second clock frequency which is different from the first clock frequency, and a measurement unit that is provided with a time-to-digital conversion circuit which converts time into a digital value by using the first clock signal and the second clock signal.

An apparatus includes a capacitor, a reference voltage, an input signal to be measured, and a frequency calculation circuit. The frequency calculation circuit is configured to select a capacitance value for the capacitor, charge the capacitor with the reference voltage, discharge the capacitor to a threshold voltage, and, based on a comparison of time to discharge the capacitor to the threshold voltage with a clock cycle of the input signal, determine a frequency of the input signal.

A method for frequency estimation in a power system. The method includes detecting a condition of the power system, applying a first estimation process to a voltage signal of the power system responsive to a normal condition being detected, and applying a second estimation process to a current signal of the power system responsive to a fault condition being detected. The condition of the power system is detected utilizing a protective device. The condition of the power system includes one of a normal condition and a fault condition.

A method for frequency estimation in a power system. The method includes detecting a condition of the power system, applying a first estimation process to a voltage signal of the power system responsive to a normal condition being detected, and applying a second estimation process to a current signal of the power system responsive to a fault condition being detected. The condition of the power system is detected utilizing a protective device. The condition of the power system includes one of a normal condition and a fault condition.

A system frequency detector includes an orthogonal coordinate signal generator generating an orthogonal two-phase voltage signal from a three-phase voltage signal of three-phase alternating current power by converting the three-phase voltage signal into a two-phase voltage signal orthogonal to the three-phase voltage signal, converting the two-phase voltage signal into a voltage signal of a rotating coordinate system, calculating a moving average of the voltage signal of the rotating coordinate system, and performing an inverse transformation of the voltage signal of the rotating coordinate system after calculating the moving average. A frequency calculator calculates an angular frequency based on the two-phase voltage signal, and an arithmetic unit calculates a system frequency of the power system from the angular frequency. The frequency calculator includes a rate limiter in series with the arithmetic unit, the rate limiter limiting a change of the system frequency equal to or greater than a prescribed change rate.