Methods and apparatus to detect blank images in a digital video broadcast signal are disclosed. An example method of detecting a blank image includes receiving a compressed digital image including a plurality of DC values, analyzing a total number of bits in the digital image to determine if the digital image has a data size small enough to be a blank frame candidate, if the data size is small enough for the digital image to be a blank frame candidate, analyzing multiple areas of the digital image to determine if the multiple areas exhibit substantially a same complexity, if the multiple areas exhibit substantially the same complexity, determining a number of DC values in the plurality of DC values that meet a criterion, comparing the determined number of DC values meeting the criterion to a threshold, and identifying the received digital image as a blank image if the determined number of DC values exceeds the threshold.

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.

A waveform separator system for determining DC leakage current flowing through an insulating structure in a high voltage direct current power system, wherein the DC leakage current is a composite DC current comprising one or more high magnitude momentary spikes, and having a DC component and an AC component includes: (1) a waveform separator configured to receive the composite DC current flowing through the insulating structure and to separate the composite DC current into corresponding direct current (DC) and alternating current (AC) components wherein the AC component has a first rate of change, and wherein the DC component has a second rate of change, and wherein the first rate of change is greater than the second rate of change; (2) at least one comparator configured to receive the AC component and produce at least one corresponding digital signal; and (3) a processor configured to: (a) receive the at least one corresponding digital signal and the DC component, (b) analyze the at least one corresponding digital signal and the DC component, and; (c) determine a resultant leakage current flowing through the insulating structure.

A magnetic core is electromagnetically coupled to two conductors that allow an AC current to flow through. An exciter is configured to supply a winding with an excitation current that is an alternating current. A current detector is configured to detect a current flowing through the winding. A DC component detector is configured to detect a DC component level from the current detected with the current detector. Two contact elements are respectively disposed along the two conductors. A discrimination controller is configured to: turn the two contact elements on when the DC component level detected with the DC component detector is less than or equal to a threshold; turn the two contact elements off when the DC component level detected with the DC component detector is greater than the threshold; and turn the two contact elements off in de-energized condition.

A current detecting apparatus measures an input current or an output current of an electronic apparatus. The current detecting apparatus includes a current detecting module, a direct-current measurement module and a current detecting module. The current detecting module includes a coil configured to electromagnetically couple to a path of an input or a path of an output of the electronic apparatus to obtain a first voltage signal. The direct-current measurement module measures the path of the input or the path of the output to obtain a second voltage signal. The current detecting module converts the first voltage signal into a first current command, and converts the second voltage signal into a second current command. The first current command is an alternating-current component of the input current or the output current. The second current command is a direct-current component of the input current or the output current.

A method and a device for measuring a current flowing through a switch which has an unknown inner resistance and two connections, a voltage difference being measured at the switch. During operation, the current provided by an AC voltage source, which is part of an AC voltage circuit connected in parallel with the switch, is superimposed on the current to be measured, the current flowing through the switch, by way of the AC voltage source. Both the amplitude and the frequency of the current provided by the AC voltage source are known. An AC voltage component of the voltage difference and the amplitude of the component are ascertained, and the current between the connections is ascertained and output proportionally to the amplitude of the current of the AC voltage source.

System and methods for high accuracy, non-intrusive current sensing are provided. A system may include two magnetic field sensors configured for differential sensing. The system may further include frontend circuitry configured to remove direct current (DC) offset of the magnetic field sensors, upconvert the outputs of the magnetic field sensors, and filter out at least one frequency component from the up-converted signals. The system may receive output signals from the front-end circuitry corresponding to each sensor. The system may further calculate a differential signal based on the output signals. The system may apply optimal detection based on the differential signal and a reference signal to calculate a measurement of current flow. The system may determine a phase angle measurement between the differential signal and the reference signal to calculate a direction of the current flow in the conductor and output various measurement information related to the detected current.

Bias tees, according to certain embodiments of the present invention, include switches in the AC signal path, the DC signal path, or both, to improve the capability of the bias tees to be used for high impedance AC measurement, low current DC measurement, or both. Optical control of the switches, as well as control of the switches using a DC bias present within the AC signal input to the bias tee, is described. Including a set of diodes into the DC signal path, rather than a switch, provides enhanced capability of the bias tee to be used for high impedance AC measurements.

A test and measurement probe system, including an input to receive an input signal, the input signal including a low frequency (LF) and/or direct current (DC) component and an alternating current (AC) component, an extractor circuit, such as an AC coupling circuit or a LF and/or DC rejection circuit, configured to receive the input signal and to separate the AC component and the LF and/or DC component from the input signal, a first output to output the alternating current component to the test and measurement instrument, and a second output to output the direct current component to the test and measurement instrument. In some embodiments, the LF and/or DC component is digitized prior to being output by the second output.