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.

A current sensor including a housing, the housing including a first module adapted to be clamped around a wire part of a power cable; a second module having a processing unit and a communication unit; the first module further including a device to measure the current through the wire of said power cable and to send the measured current to the processing unit through a first communication link. The processing unit includes a first time tracker; where the processing unit further includes software/hardware to increment the first time tracker if the measured current is above a first predetermined threshold and in that the communication unit includes a GSM module adapted to wirelessly transmit the value of the first time tracker.

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 voltage on-off detector includes an inverter between a first voltage source and a first node and having an input terminal that receives a third voltage, a first transistor having a first gate, and a first source and a first drain between the first node and a second voltage source, a second transistor having a second source connected to the second voltage source, and a second gate and a second drain connected to the first node, and an amplifier having an input terminal connected to an output terminal of the inverter and configured to output a first voltage from the first voltage or a second voltage from the second voltage source based on or in response to an output of the inverter.

A voltage on-off detector includes an inverter between a first voltage source and a first node and having an input terminal that receives a third voltage, a first transistor having a first gate, and a first source and a first drain between the first node and a second voltage source, a second transistor having a second source connected to the second voltage source, and a second gate and a second drain connected to the first node, and an amplifier having an input terminal connected to an output terminal of the inverter and configured to output a first voltage from the first voltage or a second voltage from the second voltage source based on or in response to an output of the inverter.

A circuit board which includes a circuit that measures an input voltage and an output voltage in a voltage converter that converts the input voltage which is a difference between first and second voltages into the output voltage which is a difference between third and second voltages, may include: first to fourth resistor circuits respectively including first to fourth resistor element groups; a first differential amplifier circuit configured such that the first voltage is inputted via the first resistor element group and the second voltage is inputted via the second resistor element group; and a second differential amplifier circuit configured such that the third voltage is inputted via the third resistor element group and the second voltage is inputted via the fourth resistor element group. The second and fourth resistor element groups may be arranged to be adjacent to each other between the first and third resistor element groups.

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.

A signal detection circuit is provided, and includes an input switch circuit, an amplitude detection circuit, a clock generating circuit, and an integration circuit. The input switch circuit receives a reference voltage and an input voltage and selectively outputs the reference voltage or the input voltage. The amplitude detection circuit detects an output of the input switch circuit to generate an amplitude voltage. The clock generating circuit controls the input switch circuit to alternately enter first and second phases, the input switch circuit is controlled to output the reference voltage in the first phase, and output the input voltage in the second phase. The integration circuit receives the amplitude voltage as an input, and generates an integration voltage corresponding to an accumulation result within a predetermined time interval. The predetermined time interval includes at least one period that cycles between the first phase and the second phase.

A signal detection circuit is provided, and includes an input switch circuit, an amplitude detection circuit, a clock generating circuit, and an integration circuit. The input switch circuit receives a reference voltage and an input voltage and selectively outputs the reference voltage or the input voltage. The amplitude detection circuit detects an output of the input switch circuit to generate an amplitude voltage. The clock generating circuit controls the input switch circuit to alternately enter first and second phases, the input switch circuit is controlled to output the reference voltage in the first phase, and output the input voltage in the second phase. The integration circuit receives the amplitude voltage as an input, and generates an integration voltage corresponding to an accumulation result within a predetermined time interval. The predetermined time interval includes at least one period that cycles between the first phase and the second phase.