An absence of voltage indicator has an isolation circuit, an FM modulator attached to the isolation circuit, a reference oscillator, and a mixer attached to the reference oscillator and the FM modulator, wherein the output of the mixer is the difference of the two signals. In one embodiment, the FM modulator includes a variable capacitor which varies in response to a voltage in parallel to a fixed capacitor and an inductor in parallel to the capacitors.

An absence of voltage indicator has an isolation circuit, an FM modulator attached to the isolation circuit, a reference oscillator, and a mixer attached to the reference oscillator and the FM modulator, wherein the output of the mixer is the difference of the two signals. In one embodiment, the FM modulator includes a variable capacitor which varies in response to a voltage in parallel to a fixed capacitor and an inductor in parallel to the capacitors.

A switching arrangement for monitoring AC signals includes: one or a plurality of comparators, to which an AC signal to be monitored or a signal obtained therefrom is feedable in each case at a first comparison input, for comparison with a defined amplitude threshold value present at a second comparison input, so as to generate a first output signal at an output; a zero crossing detector, to which a reference signal or a signal obtained therefrom is feedable at a monitoring input, so as to generate a second output signal at an output of the zero crossing detector; a first timing element downstream of the zero crossing detector configured to generate a first clock signal as a function of the second output signal; and a second timing element downstream of the zero crossing detector configured to generate a second clock signal as a function of the second output signal.

Amplifying circuitry configured such that when a detection circuit detects an abnormal state in which the level of signals input to a main amplifying circuit exceeds a normal range, a control circuit sets the state of integration of signals in the integration circuit to a default state. When the detection circuit detects the abnormal state and then detects that an operating state returns to a normal state in which the level of signals input to the main amplifying circuit is included in the normal range, the control circuit cancels the setting of the default state in the integration circuit.

Amplifying circuitry configured such that when a detection circuit detects an abnormal state in which the level of signals input to a main amplifying circuit exceeds a normal range, a control circuit sets the state of integration of signals in the integration circuit to a default state. When the detection circuit detects the abnormal state and then detects that an operating state returns to a normal state in which the level of signals input to the main amplifying circuit is included in the normal range, the control circuit cancels the setting of the default state in the integration circuit.

A magnetic field detection device includes a magnetic field detection element, a modulation coil, and a demodulator. The magnetic field detection element has a sensitivity axis in a first direction. The modulation coil is configured to apply, to the magnetic field detection element, an alternating current magnetic field having a first frequency and a component in a second direction, the second direction being orthogonal to the first direction. The demodulator is configured to demodulate an output signal having the first frequency and outputted from the magnetic field detection element, and detect, on a basis of an amplitude of the output signal, an intensity of a measurement magnetic field to be received by the magnetic field detection element.

A magnetic field detection device includes a magnetic field detection element, a modulation coil, and a demodulator. The magnetic field detection element has a sensitivity axis in a first direction. The modulation coil is configured to apply, to the magnetic field detection element, an alternating current magnetic field having a first frequency and a component in a second direction, the second direction being orthogonal to the first direction. The demodulator is configured to demodulate an output signal having the first frequency and outputted from the magnetic field detection element, and detect, on a basis of an amplitude of the output signal, an intensity of a measurement magnetic field to be received by the magnetic field detection element.

An electronic circuit according to an embodiment includes a clock generator, a delay element, a first electromagnetic coupler, a first frequency converter, a second electromagnetic coupler, a second frequency converter, a controller and an output device. The clock generator is configured to generate a first clock signal. The delay element is configured to output a second clock signal which has a phase delayed with respect to the first clock signal. The first electromagnetic coupler is configured to transmit one of the first and second clock signals by electromagnetic coupling. The first frequency converter is driven by the one of the first and second clock signals transmitted from the first electromagnetic coupler and is configured to convert a first input signal to a first signal with a first frequency corresponding to the one of the first and second clock signals.

A current transformer (CT) for the purpose of, for example, current measurement, that uses a power line as a first coil and a second coil for measurement purposes, is further equipped with a third coil. Circuitry connected to the third coil is adapted to measure a signal therefrom. The measured signal from the third coil is compared to a signal measured from the second coil and based on the results, internal CT parameters are determined allowing calibration of actual results to expected results thereby providing an improved accuracy. This is especially desirable when using the CT for measurement of the like of current or phase of the primary coil when measurements are adjusted using the newly determined calibration parameters.

A current transformer (CT) for the purpose of, for example, current measurement, that uses a power line as a first coil and a second coil for measurement purposes, is further equipped with a third coil. Circuitry connected to the third coil is adapted to inject a known reference signal to the third coil of the CT. The injected reference signal, i.e., current, generates signals in the first and second coils of the CT. The signal generated in the second coil is compared using circuitry attached thereto to the reference signal. Based on the results, and the difference between the expected results and the actual results, updated calibration parameters are determined. These provide improved accuracy when using the CT, for example for measurement of the like of current or phase of the primary coil when measurements are adjusted using the newly determined calibration parameters.