Abstract: An electric vehicle supply equipment (EVSE) is provided with an integrated arc fault detection circuit interruption (AFCI) device to supply electricity to an electric vehicle (EV) being a load. The EVSE comprises a coupler and an AFCI device including: a controller including a processor and a memory, circuitry and computer-readable firmware code stored in the memory which, when executed by the processor, causes the controller to: detect an arcing level of arcing between the coupler and a charge port of the EV or any other series or parallel arcing within the EVSE, compare the arcing level to a threshold level to determine a hazardous nature of arching, and analyze the arcing level to determine not only if it is currently hazardous but if it is likely to become hazardous in a near term and recommend repair or replacement of the coupler and the charge port before damage occurs.

Abstract: This document discloses a solution for a method of monitoring an electric power grid. According to an aspect, a method comprises: obtaining, on a basis of one or more physical stimuli generated endogenously in the electric power grid, a first set of measurement data associated with a first location of the electric power grid, the physical stimuli belonging to nominal or near-nominal operation of the electric power grid and generating at least one of voltage fluctuation and current fluctuation that exceeds at least one threshold; computing a grid strength of the first location of the electric power grid on the basis of the first set of measurement data; mapping the grid strength to a grid strength of a second location of the electric power grid on the basis of the first set of measurement data and correlation between electrical characteristics of the first location and the second location.

Abstract: A test instrument connectable to a cable television (CATV) network to provide a high resolution time domain reflectometry (TDR) in a fault location measurement is disclosed. The test instrument may have a port connectable to a test point in the CATV network. The test instrument may also have a processing circuit to perform a calibration measurement and a fault location measurement by transmitting frequency-chirped probe pulses into a closed calibration circuit within the test instrument, and receiving return signals at an analog-digital converter in the test instrument. The processing circuit may resample the calibration measurement and the fault location measurement at a high sampling rate, cross-correlate the fault location with the calibration measurement to generate a cross-correlation TDR waveform, and generate a new TDR waveform using a refinement processing technique to remove echoes from the cross-correlation TDR waveform.

Abstract: A fault isolating device for use in a microgrid disconnected from a main power grid includes a voltage meter for detecting a voltage anomaly indicative of an electrical fault, a timer for establishing a time window that begins and ends a predetermined time after a voltage anomaly is detected, a switch that is opened at the start of the time window, and a microcontroller that determines whether to leave the switch open to isolate a faulted portion of the microgrid or to close the switch. A plurality of fault isolating devices can be distributed throughout a microgrid to isolate a faulted branch or faulted branches of an islanded microgrid without interfering with normal fuse operation when the microgrid is connected to the main power grid.

Abstract: The present disclosure provides techniques for estimating network states using asynchronous measurements by leveraging network inertia. For example, a device configured in accordance with the techniques of the present disclosure may receive electrical parameter values corresponding to at least one first location within a power network and determine, based on the electrical parameter values and a previous estimated state of the power network, an estimated value of unknown electrical parameters that correspond to a second location within the power network. The device may further cause at least one device within the power network to modify operation based on the estimated value of the unknown electrical parameters. The leveraging of network inertia may obviate the need for probabilistic models or pseudo-measurements.

Abstract: A diagnostic method of switchgear and a device of switchgear that allow regularly grasping a state with high accuracy with a simple configuration is provided. The diagnostic method of switchgear includes: obtaining signals from an acceleration sensor mounted to a switchgear and a load current flowing through the switchgear; determining a frequency to be focused from a spectrum analysis result of the signals from the acceleration sensor in an advance preparation phase of diagnosis of the switchgear, generating learning data using at least the frequency and the load current as feature values; and regularly diagnosing the state of the switchgear from the feature values obtained during diagnosis and the learning data during the diagnosis of the switchgear.

Abstract: A system for detecting water trees in branching underground electrical cables includes a pulse generator configured to inject a pulse into a first underground cable that branches into a second underground cable and a third underground cable. The system includes a first sensor associated with the first cable, a second sensor associated with the second cable, and a third sensor associated with the third cable. The system includes a control device configured to obtain a first, second, and third signal associated with the first, second and third sensors, respectively. The control device determines a lead-lag relationship between the second and third signals and determines presence of a water tree within at least one of the second and third cable based on the lead-lag relationship. When presence of a water tree is determined, the control device generates a control action associated with repairing or replacing the second and/or third cable.

Abstract: An example device includes at least one processor configured to receive electrical parameter values corresponding to at least one first location within a power network. The at least one processor is further configured to determine, using matrix completion and based on the at least one electrical parameter value, an estimated value of at least one unknown electrical parameter. The at least one unknown electrical parameter corresponds to a second location within the power network. The at least one processor is also configured to cause at least one device within the power network to modify operation based on the estimated value of the at least one unknown electrical parameter.

Abstract: The present disclosure provides a method for detecting presence of a bidirectional amplifier. At least one radio signal is transmitted by a detection device, the at least one radio signal being a two-tone stimulus. The at least one transmitted radio signal is received by the bidirectional amplifier. The radio signal is processed by the bidirectional amplifier, thereby amplifying the radio signal while generating third order or higher intermodulation products such that an amplified radio signal is generated that includes the third order or higher intermodulation products. The amplified radio signal is transmitted. The amplified radio signal is received by the detection device. The amplified radio signal is analyzed by the detection device, thereby obtaining detection results. Further, a system for detecting presence of a bidirectional amplifier is shown.

Abstract: In one embodiment, the PIM load includes a variable attenuator; a detector configured to detect a signal characteristic associated with a signal received by the PIM load; and a controller configured to control the variable attenuator based on output from the detector.

Abstract: Disclosed herein are methods, systems, and devices for system event detection associated with power grid components. Methods include detecting, at a plurality of sensors, emissions from a system event associated with at least one winding of a power component. Methods also include determining, using a processor, a plurality of event parameters based, at least in part, on measurements made by the plurality of sensors, the event parameters identifying arrival times of the emissions at each of the plurality of sensors. Methods further include generating, using the processor, an output identifying an estimate of a position of the system event within the power component, the estimate being generated based, at least in part, on the arrival times identified by the plurality of event parameters.

Abstract: A dynamic dual-port passive intermodulation reference signal generator for calibrating an intermodulation testing device includes: a power allocation coupling network, a non-linear device located under a biasing condition, and a voltage modulation module. Extraction of a carrier signal is performed through a power distribution coupling network; the carrier signal as extracted excites a non-linear device to generate an intermodulation signal; this part of signal, together with the excitation signal, is coupled back to two ports of the generator by the same power distribution coupling network, thereby forming reflected and transmitted reference intermodulation levels as reference sources for calibrating the intermodulation testing apparatus.

Abstract: In the method for transmitting data representing an ultrasonic measurement signal of an ultrasonic measuring device, in particular for a vehicle, from a transmitter to a receiver a digitized analog ultrasonic measurement signal is provided in the transmitter. On the transmitter side the ultrasonic measurement signal is sampled at a multiple of its frequency and divided into individual successive blocks of sampling values. The sampling values of the sampled ultrasonic measurement signal are transformed in blocks into the frequency range. Those frequency portions of the spectrum whose amplitude is smaller than a presettable threshold value, or the frequency portions of the spectrum above an upper frequency limit value and/or below a lower frequency limit value are removed. The amplitude range covered by the remaining frequency spectrum is scaled by a scaling factor for further reduction of the data. The data of each block with the scaling factor assigned to the respective block are transmitted to the receiver.

Abstract: An excitation core includes an annular strip-shaped magnetic substance, in which both ends of the strip-shaped magnetic substance are overlapped in a thickness direction and are in contact with one another. A sensor head includes: this excitation core and a magnetism collecting body. The magnetism collecting body includes a strip-shaped first magnetism collector and a strip-shaped second magnetism collector, the first magnetism collector having both ends thereof in contact with both ends of the second magnetism collector to form the annular magnetism collecting body, the magnetism collecting body being disposed on an inside or an outside of the reinforcing body.

Abstract: Provided are a gas insulated switchgear (GIS) internal video monitoring system and a GIS internal video monitoring method. The GIS internal video monitoring system includes a GIS video sensor installed on a GIS enclosure and configured to acquire an open/close state of a GIS internal conductor in a real time manner, an intelligent power source module, a video server, and a video monitoring background system configured to control the intelligent power source module to supply power to the video sensor, where the GIS video sensor is connected with the video monitoring background system through the video server.

Abstract: A single-ended traveling wave fault location estimation is calculated using this disclosure, and a confidence level is determined based on available independent fault location estimations. Hypothesis are calculated based on traveling wave times and values, wherein the values indicate a polarity that is the same as the first received traveling wave. Hypothesis are then compared against results of other fault location estimations, and confidence levels assigned accordingly. The fault location is then calculated and displayed based on the hypothesis and confidence levels.

Abstract: A power distribution unit and a fault detecting method applied in the power distribution unit are disclosed herein. The power distribution unit includes an input terminal, an insulation fault detection circuit and a processing circuit. The input terminal is electrically coupled to a positive power line and a negative power line, and configured to receive a high voltage direct current (HVDC) voltage. The insulation fault detection circuit is configured to detect an insulation resistance value between a ground terminal and the positive power line or the negative power line. The processing circuit is configured to output a warning signal according to the insulation resistance value.

Abstract: A component monitoring system structured to monitor circuit breaker assembly component characteristics is provided. The component monitoring system includes a record assembly, a number of vibration sensor assemblies, a comparison assembly, and an output assembly. The record assembly includes selected nominal data for a selected circuit breaker component. The vibration sensor assembly is structured to measure a number of actual component characteristics for a substantial portion of the circuit breaker assembly and to transmit actual component characteristic output data. The comparison assembly is structured to receive an electronic signal from said record assembly and said sensor assemblies, to compare each sensor assembly actual component characteristic output data to said selected nominal data and to provide an indication signal as to whether said sensor assembly output data is acceptable when compared to the selected nominal data. The output assembly includes a communication assembly and an output device.

Abstract: An arc detection apparatus is provided. The arc detection apparatus detects an arc using an electrical energy, eliminates the possibility of a false arc detection caused by noise due to a power environment, increases accuracy of arc detection, and prevents fires that may occur in a home or an industrial site due to an arc occurrence.

Abstract: A semiconductor device includes first and second pads separated from each other, first and second test elements connected to the first and second pads and connected to each other in parallel between the first and second pads, a first diode connected to the first test element in series, and a second diode connected to the second test element in series.

Abstract: Systems and methods for testing a wireless device having a beamforming circuit are disclosed herein. An exemplary system includes a shielded test enclosure, a wireless channel emulator, and a test instrument. The shielded test enclosure provides a cable-free connection between the wireless device and the wireless channel emulator, thereby allowing for testing of various types of wireless devices, particularly those that do not have radio-frequency (RF) connectors. The shielded test enclosure is smaller in size and less-expensive than traditional multi-probe anechoic chambers. In one example application, the shielded test enclosure is used to house a multiple-input multiple-output (MIMO) antenna array of a wireless device and a probe antenna array. The probe antenna array is coupled to the wireless channel emulator and used to receive signals from MIMO antenna arrays of various sizes thereby eliminating the need to uniquely tailor the probe antenna array to any specific MIMO antenna array.

Abstract: An electronic device includes a first connection interface and a second connection interface configured to be electrically connected to at least one host system, a transmission control device, a data access device, and a channel-detecting device. The transmission control device includes a first communication channel electrically connected to the first connection interface and a second communication channel electrically connected to the second connection interface. The transmission control device determines a connection state according to impedance information and provides corresponding operation functions for at least one host system according to the connection state. The data access device is electrically connected to the transmission control device, and is configured to receive data transmitted by the host system. The channel-detecting device detects the impedance information between one or both of the first connection interface and the second connection interface and the at least one host system.

Abstract: The present disclosure relates to a method for testing connectivity. The method is applied to an electronic equipment which is disposed include two test units (e.g. network interface controller, RJ-45 connector) and a network transformer. The test unit couple to the network transformer so that can send a high frequency test signal or a low frequency test signal to the network transformer respectively. When the test unit receives a low frequency response signal, it means correspond internal circuitry of the network transformer does not have a open circuit fault. When the test unit does not receive a high frequency response signal, it means correspond pins of the network transformer does not have a short circuit fault.

Abstract: A method for monitoring partial discharges in an electric power transmission system includes the steps of: detecting electric pulses from a component of the electric power transmission system, repeating a battery of different tests adapted to provide each a result indicative of partial discharge activity, the tests being continuously performed in succession one after the other in a preset period of time, each including a set of operations of acquisition and evaluations of the detected electrical pulses, and differing each other for a plurality of different combinations of values taken by test parameters used for executing the acquisition and evaluation operations; analyzing the results obtained with time by the batteries of tests executed at different execution times in the present period of time; and generating an alarm depending on the outcome of the analysis step.

Abstract: There is provided a partial discharge sensor including a first flange formed at an end of a first conductor tube, a second flange formed at an end of a second conductor tube, a first insulating spacer sandwiched between the first flange and the second flange, a plurality of holes passing through the first flange, the first insulating spacer, and the second flange, at least two first conductors each passing through one of the plurality of holes to be disposed with electrically connected to the first flange and the second flange, a second conductor passing through one of the plurality of holes to be disposed with electrically connected to the second flange, and a second insulating spacer that insulates the second conductor and the first flange from each other.

Abstract: A smart sensor network for power grid health monitoring includes a plurality of spaced sensors that are magnetically coupled to the power transmission line to be monitored. The sensors include a signal injection unit and a signal sensing unit. As such, one of the sensors acts to inject, via its signal injection unit, a high frequency signal through the magnetic coupling into the power transmission line, while sensors on either side of the signal injecting sensor act to block the injected signal, which is then detected by the signal sensing unit of the injecting sensor, and is used to measure the impedance of the power transmission line segment being analyzed. Based on the difference between a pre-measured impedance of the power transmission line being monitored and the actual impedance value of the power transmission line being measured by the sensor, the health of the power line can be obtained.

Abstract: Method and system allowing more accurate detection and identification of unwanted arcing include novel processing of signal voltage representing recovered power-line current. In one implementation, arc-faults are detected based on numerical analysis where individual cycles of line voltage and current are observed and data collected during each cycle is processed to estimate likelihood of presence of arc-event within each individual cycle based on pre-defined number of arc-events occurring within pre-defined number of contiguous cycles.

Abstract: A method for intermodulation measurement for locating points in a signal transmission path for a high-frequency signal that are faulty with regard to HF transmission properties of the signal transmission path, by generating a first HF signal uTest, having a carrier frequency f1 and a digital signal uCode modulated thereon; generating a second HF signal u2 having a frequency f2; introducing the first HF signal uTest and the second HF signal u2 into the signal transmission path at a predetermined introduction point; receiving an intermodulation product, which is generated in the signal transmission path from the first HF signal and the second HF signal at at least one faulty point, as an intermodulation product signal uRX; recovering a digital signal udemod from uRX; and determining a time shift tx between the digital signal uCode and the recovered digital signal udemod. The invention further relates to a measuring device for performing this method.

Abstract: Various devices, systems and methods are disclosed where a noise signal component of a sensor signal is used to obtain information about a sensor device. A device may include an evaluation circuit that is configured to receive a sensor signal having a noise signal component, and the evaluation circuit is further configured to evaluate the noise signal component to obtain information about a sensor device generating the sensor signal.

Abstract: In order to determine the occurrence of a fault, notably transient, in an electrical distribution network, a method and a device are developed based on the determination of the frequency (f) of the current signal circulating in a phase of the network. Notably, the difference between the determined frequency (f) and the natural frequency (f0) of the network is compared to a threshold.

Abstract: Methods, systems, and apparatus for circuit breakers with integrated safety, control, monitoring, and protection features. In one aspect, a circuit breaker includes, an input and an output, a switch coupled between the input and the output, a sensor configured to measure the current flowing from the input to the output, and a control system coupled to the sensor and the switch, wherein the control system is configured to perform operations including comparing a rate of change of the current measured by the sensor to a threshold rate of change of current, determining that the rate of change of the current measured by the sensor exceeds the threshold rate of change of current for at least a predetermined period of time, and as a consequence of determining that the rate of change of current exceeds the threshold rate of change, opening the switch, thereby disconnecting the input from the output.

Abstract: Described are methods and circuits for margin testing digital receivers. These methods and circuits prevent margins from collapsing in response to erroneously received data, and can thus be used in receivers that employ historical data to reduce intersymbol interference (ISI). Some embodiments detect receive errors for input data streams of unknown patterns, and can thus be used for in-system margin testing. Such systems can be adapted to dynamically alter system parameters during device operation to maintain adequate margins despite fluctuations in the system noise environment due to e.g. temperature and supply-voltage changes. Also described are methods of plotting and interpreting filtered and unfiltered error data generated by the disclosed methods and circuits. Some embodiments filter error data to facilitate pattern-specific margin testing.

Abstract: Method and system for implementing multiple user-initiated self-test sequences in a multifunction circuit breaker device uses a single test input to initiate both arc fault and ground fault testing while at the same time allowing the multifunction circuit breaker device to continue detecting actual arc faults and ground faults in near real time. Having one test input for multiple self-test sequences significantly reduces the number of mechanical and electrical components required by the circuit breaker device. The multifunction circuit breaker device also distinguishes between a simulated ground fault and an actual ground fault and avoids automatically tripping upon successful completion of the ground fault self-test sequence unless and until all self-test sequences have passed. In this way, users are not given a potentially incorrect indication that the multifunction circuit breaker device is working properly.

Abstract: An apparatus and a method for detecting a dielectric breakdown in an eco-friendly vehicle are provided. The apparatus includes a measurer that is configured to measure resistance values of insulation resistors disposed across a high voltage battery and a controller that is configured to measure a voltage applied to the insulation resistor using the measurer and analyze a pattern of the measured voltage to detect a dielectric breakdown portion.

Abstract: An integrated circuit is described herein. According to one or more embodiments, the integrated circuit includes a local oscillator with a voltage-controlled oscillator (VCO) that generates a local oscillator signal. Further, the integrated circuit includes a frequency divider coupled to the VCO downstream thereof. The frequency divider provides a frequency-divided local oscillator signal by reducing the frequency of the local oscillator signal by a constant factor. A first test pad of the integrated circuit is configured to receive a reference oscillator signal. Further, the integrated circuit includes a first mixer that receives the reference oscillator signal and the frequency-divided local oscillator signal to down-convert the frequency-divided local oscillator signal.

Abstract: A unique electrical system includes a first electrical component and a second electrical component. A conductor electrically couples the first electrical component with the second electrical component. A sensor is constructed to sense an AC power flow in the conductor and output an AC signal proportional to the AC power flow. A band-pass filter is in electrical communication with the sensor and constructed to receive and filter the AC signal and to generate an AC voltage proportional on the AC signal. A controller is in electrical communication with the band-pass filter, and is operative to receive and sample the AC voltage. The controller is configured to execute program instructions to sum sequential AC voltage values received from the band-pass filter over a sample time period, and to determine whether an arc fault has occurred based on the summed AC voltage values.

Abstract: In accordance with embodiments disclosed herein, there are provided apparatus, systems, and methods for identifying cable-level faults in a copper plant of a DSL system. For example, such means may include identifying a group of Digital Subscriber Lines (DSL lines) within a common cable; determining a baseline of physical line characteristics for each of the DSL lines in the group; collecting current physical line characteristics for each of the DSL lines in the group; determining a physical line characteristics delta for each of the DSL lines in the group by comparing the current physical line characteristics to the baseline of physical line characteristics for each of the respective DSL lines; and indicating a defect in the common cable based on a quantity of the DSL lines in the group for which the respective DSL line's physical line characteristics delta exceeds a threshold. Other related embodiments are disclosed.

Abstract: A partial discharge signal processing device of the present invention is provided with: a partial discharge signal receiving unit disposed inside a high voltage electric machine device; a partial discharge signal processing unit; and a coaxial cable connecting the partial discharge signal receiving unit and the partial discharge signal processing unit. In addition, the partial discharge signal receiving unit comprises an electromagnetic wave receiving unit that receives electromagnetic waves generated by partial discharge. Further, the partial discharge signal processing unit comprises: a detection unit that detects a partial discharge signal transmitted through the coaxial cable; a band limiting unit that limits the frequency bandwidth of the partial discharge signal; an attenuation amount correction unit that corrects an attenuated partial discharge signal; and a signal output unit that outputs, to an external device, the corrected partial discharge signal.

Abstract: Determining a property of an electrical signal at a node instant at the current instant (INSTC); determining a previous function indicative of a property of the signal at the node at a previous instant; determining an error function in a previous frequency estimation at the node at a previous instant; determining a first current function indicative of the property of the signal at the node at INSTC in accordance with the determined property, the previous function, and the error function; receiving, from another node, a second current function indicative of a property of an electrical signal at the at least one other node at INSTC; combining the first current function and the second current function to produce a current combined function (CCF) indicative of a property of the signal at the node at INSTC; and estimating a current frequency of the signal at the node in accordance with the CCF.

Abstract: In a semiconductor device, received signals of different frequency bands are input selectively to low noise amplifiers. A plurality of primary inductors are coupled between differential output nodes of the respective low noise amplifiers. A secondary inductor is provided commonly for the primary inductors, and magnetically coupled to the primary inductors. A demodulator converts a received signal transmitted from one of the primary inductors to the secondary inductor by electromagnetic induction, into a signal of a low frequency.

Abstract: A test system for testing a plurality of devices under test (DUTs) is provided. The test system comprises a test signal generator configured to generate test signals to be transmitted to the DUTs, wherein the test signals comprise at least one synchronization signal. The test signal generator is configured to broadcast the at least one synchronization signal to the DUTs. It is thereby possible to simultaneously test more than one DUT.

Abstract: An electric arc detection device samples first, second and third filterings of a signal in a current window and in another window. A correlation is determined between first filtering samples of the current and the other window, a correlation is determined between second filtering samples of the current and the other window, and a correlation is determined between third filtering samples of the current window and the other window. An arc is then detected as a function of the correlations.

Abstract: A passive intermodulation (“PIM”) distortion test apparatus includes a housing, hammering elements disposed within the housing, each hammering element including a moveable striking member, a strike plate positioned above the hammering elements, where a bottom surface of the strike plate is positioned at a distance above the hammering elements such that the moveable striking members of the hammering elements impact the strike plate when moved into their activated positions, and a retaining member that is configured to hold a device under test on a top surface of the strike plate while a PIM distortion test is performed on the device under test.

Abstract: Method for determining the overall length (GL) of a jib (1, 4) of a crane in a wear-free manner, characterized in that a signal is coupled in at a first point (2, 5) of the jib (1, 4) and is coupled out at a second point (3, 6) of the jib (1, 4), the overall length (GL) being determined from the time required for the signal to go from the first point (2, 5) to the second point (3, 6).

Abstract: A sensing apparatus includes a probe and a sensing module. The sensing module includes a material sensing circuit, an operation unit and a signal output circuit. The sensing module generates a frequency sweep signal and sends the frequency sweep signal to the probe to sense a status of a material. The frequency sweep signal is a plurality of signals having different frequencies from each other in a predetermined frequency range. When the frequency sweep signal touches the material, an equivalent capacitance of the material is utilized to generate a reflected signal. The material sensing circuit receives the reflected signal and sends the reflected signal to the operation unit. The operation unit operates the reflected signal to generate a waveform signal to determine the status of the material. The operation unit utilizes an impedance spectrum to determine the status of the material.

Abstract: A method for detecting failures in electrical cable assemblies is provided. A cable test instrument obtains frequency domain data representing electrical characteristics of a cable link under test. A number of connectors in the cable link under test is determined based on the obtained frequency domain data. An estimated location of each of the connectors along the length of the cable link under test is determined by the cable test instrument. The connectors are ranked in accordance with their respective contribution to detected failures in the cable link under test.

Abstract: A method of controlling a power generation system following a transient grid event, and a system and controller to control the power generation system are described. The method includes sensing a rate of change of electrical frequency at terminals of a generator, determining a rate of change of shaft line acceleration, and identifying the transient grid event based on the rate of change of shaft line acceleration. The method also includes triggering an action to recover from the transient grid event when the rate of change of electrical frequency exceeds a first specified value and the rate of change of shaft line acceleration exceeds a second specified value for a specified duration.

Abstract: In a method for detection of an arc in a current path of a converter arrangement (2) for converting a DC input power to an output power, an arc is detected by sensing the current (4) in the current path by means of a current transformer (11), filtering the current signal (4?) with an analog band pass filter (14), converting the analog filtered current signal (4?) into a digital current signal (4??), determining the harmonic content (19) of the digital current signal (4??) and then deciding whether an arc exists if the harmonic content (19) exceeds a threshold, where the threshold is determined at the beginning as a multiple of the average harmonic content during a certain period of time of the current signal.

Abstract: A minimum level for a stimulation signal used in room correction processing is determined by measuring background noise. The stimulation signal is repeated a number of times and resulting responses are recorded. The recording responses are averaged, and the average is subtracted from each recorded response to obtain the background noise present in each recorded response. A stimulation signal to background noise ratio is computed from the stimulation signal and background noise and compared to an SNR threshold to determine if the stimulation signal level is sufficient to support the room correction processing. The background noise may be AC hum introduced electronically into the response signal, acoustic noise introduced by AC ventilation systems or noise emitting devices (refrigerators, etc), and it may be structure-born noise introduced by shaking the microphone, e.g. a bus drives by, shaking the floor the microphone is standing on.

Abstract: In monitoring an isolation of an ungrounded power grid an AC voltage source is connected to the power grid via at least one test resistor. A test signal with a periodic continuous voltage course with regard to ground and with a frequency is applied to the power grid by means of the AC voltage source. A leakage current flowing due to the test signal is measured; and an ohmic isolation resistance is determined from the leakage current. The frequency of the test signal is varied such that an active current part of the leakage current keeps a predetermined recommended value at varying leakage capacitances of the power grid. This provides for a desired level of accuracy at maximum speed of isolation or ground fault detection.