A circuit comprises: a sampling and holding circuit and a control circuit. The sampling and holding circuit is used for sampling the voltage of a voltage sampling point in a sampling stage and holding the sampling voltage of the sampling output end after the sampling stage is ended. The control circuit is used for controlling the sampling and holding circuit to enter the sampling stage when judging that the voltage of the voltage sampling point is in a sampling voltage segment according to the voltage of the voltage sampling point, and controlling the sampling stage of the sampling and holding circuit to be ended when judging that the voltage of the voltage sampling point is in a voltage inflection point according to the voltage of the voltage sampling point and the sampling voltage of the sampling output end.

A circuit comprises: a sampling and holding circuit and a control circuit. The sampling and holding circuit is used for sampling the voltage of a voltage sampling point in a sampling stage and holding the sampling voltage of the sampling output end after the sampling stage is ended. The control circuit is used for controlling the sampling and holding circuit to enter the sampling stage when judging that the voltage of the voltage sampling point is in a sampling voltage segment according to the voltage of the voltage sampling point, and controlling the sampling stage of the sampling and holding circuit to be ended when judging that the voltage of the voltage sampling point is in a voltage inflection point according to the voltage of the voltage sampling point and the sampling voltage of the sampling output end.

A motor drive apparatus includes a converter, a DC link capacitor, a plurality of inverters, a diagnosis command unit configured to give a command to one of the plurality of inverters to perform power conversion, an AC voltage detection unit configured to detect a peak value of AC voltage on an AC input side of the converter, a DC voltage detection unit configured to detect a value of DC voltage across the DC link capacitor, a calculation unit to calculate a difference between the value of DC voltage and the peak value of AC voltage, a storage unit configured to store the difference in association with the inverters, and a leakage current determination unit configured to determine that the inverter associated with the largest of the differences stored in the storage unit is the inverter that has caused the largest leakage current.

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.

Disclosed is a test device. The test device according to an embodiment of the present invention is operated by a power supply unit provided to be portable, and tests a sensor device using an alternating current of a high frequency. Therefore, the portability and operation reliability of the test device are improved, and the convenience of use can be improved since a separate wire member or the like for the operation of the test device need not be provided.

Disclosed is a test device. The test device according to an embodiment of the present invention is operated by a power supply unit provided to be portable, and tests a sensor device using an alternating current of a high frequency. Therefore, the portability and operation reliability of the test device are improved, and the convenience of use can be improved since a separate wire member or the like for the operation of the test device need not be provided.

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.

Systems and methods provide a portable, verified voltage source that allows safe testing of separate non-contact voltage measurement systems. A proving unit of the present disclosure provides a known or specified alternating current (AC) voltage output across an insulated wire, which AC voltage may be fixed or may be user-selectable through a suitable user interface. The proving unit may include a visual indicator and/or an audible indicator that provides the user with an indication confirming that the proving unit is supplying an output voltage with the specifications of the proving unit, so the user will know that the proving unit is operating normally and is ready for testing a non-contact voltage measurement system. If the proving unit cannot provide the specified voltage output, the indicator(s) provides a signal to the user that the proving unit is currently non-functional.