379 results about "High-pass filter" patented technology

The invention discloses a multi-mode hybrid energy storage cooperative control method and system for a megawatt-level network-building type energy storage power station, and the method comprises the steps: S1, collecting the frequency, voltage amplitude and phase of a power grid, and the charge state and temperature of each energy storage branch, and generating real-time monitoring data; s2, determining an operation mode of the energy storage power station based on a comparison result between the frequency deviation and the voltage deviation in the real-time monitoring data and a preset threshold value; s3, based on the operation mode of the energy storage power station, performing double-layer decomposition on the power instruction through a high-pass filter and a low-pass filter to generate a super-capacitor power instruction and a lithium battery power instruction; s4, generating an internal potential amplitude and a phase angle by adopting a virtual synchronous machine algorithm; and S5, on the basis of the amplitude and the phase angle of the internal potential and the detection result of the power grid connection state, executing switching control of a network construction type control mode or a network following type control mode. The millisecond-second level multi-time scale power optimal distribution is realized; self-adaptive inertia and voltage support is carried out; and island / grid-connected seamless switching is realized.

The invention discloses an electroencephalogram signal processing method and system based on motion artifact prediction. The method comprises the following steps: acquiring experimental electroencephalogram data when a testee executes a motion imagination task; discrete wavelet transform is carried out on experimental electroencephalogram data, and signals are decomposed into low-frequency components and high-frequency components through a low-pass filter and a high-pass filter; inputting the low-frequency component into a pre-constructed and trained ARIMA model, and predicting to obtain a linear artifact; inputting the high-frequency component into a pre-constructed and trained XGBoost regression model, and predicting to obtain a nonlinear artifact; combining the linear artifacts and the nonlinear artifacts to generate a complete artifact prediction signal; real electroencephalogram signals are separated through difference value calculation of the experimental electroencephalogram data and the artifact prediction signals. According to the method, the time sequence change of the motion artifacts is predicted by utilizing the ARIMA model, and the nonlinear artifact features are captured in combination with the XGBoost regression model, so that the motion artifacts can be effectively removed, and purer electroencephalogram signals can be recovered.

The invention discloses a composite fault signal separation method based on adaptive spectral kurtosis deconvolution. The method comprises the following steps: S1, carrying out noise reduction processing on an original composite fault signal; s2, separating the composite fault signal after noise reduction through Hilbert envelope demodulation; s3, optimizing a low-pass filter and a high-pass filter through a Bayesian objective function, and constructing a band-pass filter and a band elimination filter; and S4, carrying out iterative filtering on the composite fault signal after noise reduction through a band-pass filter and a band elimination filter, constructing a frequency-bandwidth fast spectral kurtosis graph according to a fast spectral kurtosis deconvolution method, obtaining a center frequency and bandwidth range corresponding to the maximum spectral kurtosis, and separating out the weak fault signal in the step S2. According to the method, a spectral kurtosis graph is constructed by combining a low-pass filter and a high-pass filter through a fast spectral kurtosis deconvolution method to determine the center frequency and the bandwidth range, targeted separation is carried out on composite fault signals, an initial filtering parameter range is provided for Bayesian optimization, and the fault separation efficiency and accuracy are improved.

The invention belongs to the technical field of underwater small target object analysis and recognition methods, and particularly relates to a sound signal feature optimization method for underwater small target object analysis and recognition. Comprising the following steps: 1, acquiring and processing original data; 2, eliminating interference line spectrums, and intercepting and splicing by adopting a time window to obtain a time recombination sound signal; using range transformation to optimize signal amplitude characteristics; processing the sound signal by using an FIR digital high-pass filter; obtaining an optimized signal by using a homomorphic filter; 3, extracting structural features, energy features, frequency features and sound intensity features of the optimized digital signals; step 4, sound signal feature fusion: carrying out underwater target sound signal feature fusion processing based on a canonical correlation analysis method; the invention provides a method for extracting effective sound signal data of an underwater target under the background of optimizing a complex marine environment, enhancing signal effectiveness during long-distance detection, and constructing effective sound signal features capable of being used for classification and recognition of the underwater target at the same time.

An apparatus and method are provided to correct for time-walk errors during photon detections (e.g., detecting gamma rays). A time-walk correction is determined using measurements of energy (or charge) that apply different time windows, enabling corrections accounting for variations in the ratio between fast and slow components in the detected pulse. For example, one time window can be used to integrate the leading end of the pulse, thereby predominantly measuring the fast component, while a second window is used to integrate a trailing end of the pulse to predominantly measure the slow component. Alternatively or additionally, low-pass and high-pass filters may select the slow and fast components, respectively. The time-walk correction is a function of multiple measurements representing different components (e.g., fast and slow) of the pulse shape.

The invention provides a brain image denoising method based on a U-shaped dynamic convolution multi-scale multi-branch network. The brain image denoising method comprises the steps that brain noise images to be denoised are input into three branch networks formed by U-netAM, DSHFN and MSDSRN in parallel; in the U-netAM branch, multi-level features are extracted through an encoder in sequence, after weighting is conducted through a channel and a space attention mechanism, the spatial resolution is recovered through a decoder, and a first feature map is obtained; in the DSHFN branch, the dynamic convolution kernel generates a corresponding convolution kernel in real time according to input image features, the image is decomposed into a low-frequency part and a high-frequency part, and the low-frequency part and the high-frequency part are subjected to weighted fusion after being processed by a low-pass filter and a high-pass filter respectively to obtain a second feature map; in the MSDSRN branch, adopting multi-scale depth separable convolution to extract multi-scale features in parallel, and obtaining a third feature map through residual connection and fusion; inputting the three feature maps into an FPB block for fusion to obtain a noise feature map; and performing pixel-by-pixel subtraction on the original brain noise image and the noise feature map, and outputting a denoised brain image.

The invention relates to the technical field of optical fiber sensing, in particular to a distributed optical vibration sensing early warning verification method for an island multi-source environment. Signals collected in different environments and different states are preliminarily divided into threat signals and non-threat signals, the effectiveness of data is further verified through frequency spectrum transformation, low-frequency noise and natural environment interference signals such as sea waves and wind sound are filtered out from the signals through a 5Hz high-pass filter, high-frequency noise is further suppressed by applying a wavelet denoising technology, and the non-threat signals are obtained. And useful signal features are reserved. A variational mode decomposition technology is adopted to carry out multi-scale decomposition on signals, and multiple classic features of a mode function obtained after decomposition are selected to extract feature vectors. Low-frequency effective signals are extracted, and high-frequency noise is removed, so that essential characteristics of the signals can be better captured. And the data subjected to signal processing is input into a CNN-LSTM-Attention model for deep learning analysis.

The invention discloses a beat frequency comparison device mediated by an optical frequency comb. The beat frequency comparison device comprises the optical frequency comb, a first frequency stabilized laser, a first beat frequency device, a first frequency mixer, a first high-pass filter, a second frequency stabilized laser, a second beat frequency device, a second frequency mixer, a second high-pass filter, a DDS signal generator, a third frequency mixer and a low-pass filter. Frequency-stabilized lasers output by the first frequency-stabilized laser and the second frequency-stabilized laser and an optical frequency comb output by the optical frequency comb are subjected to beat frequency in the first beat frequency device and the second beat frequency device respectively, and first beat frequency and second beat frequency are obtained; the first beat frequency and the second beat frequency are mixed with the carrier envelope offset frequency of the optical frequency comb, and a first sum frequency and a second sum frequency are filtered out; the first sum frequency obtains a synthetic frequency through direct digital frequency synthesis; the second sum frequency and the synthetic frequency are mixed in the third mixer, and then the difference frequency is filtered out through the low-pass filter. According to the invention, beat frequency comparison of frequency-stabilized lasers with different wavelengths can be realized, and the influence of the stability of the optical frequency comb is avoided.

The invention provides a phase-sensitive optical time domain reflectometer system and method, and the system comprises a first polarization-maintaining coupler which is used for dividing laser generated by a DC laser, and obtaining first laser and second laser; the optical fiber measurement front-end module is used for processing the random signal through pulse shaping and multi-carrier modulation technologies to generate an electric signal, and sequentially performing modulation, amplification, Rayleigh scattering and amplification on the first laser after the electric signal is generated to obtain amplified Rayleigh backscattered light; the second polarization-maintaining coupler is used for dividing the second laser to obtain third laser and local oscillation light; the delay optical fiber is used for processing the third laser to obtain delay light; the third polarization-maintaining coupler is used for combining the delayed light and the amplified Rayleigh backscattered light to obtain combined light; the receiver is used for processing the combined light and the local oscillation light to obtain multiple paths of target electric signals; and the oscilloscope is used for processing multiple paths of target electric signals through low-pass and high-pass filters and a phase noise compensation algorithm so as to determine power and phase distribution. The system cost can be reduced.

The invention belongs to the field of motor control, and discloses a rotating speed fluctuation suppression anti-interference control method for a low-speed permanent magnet direct drive motor. According to the method, a first-order linear active disturbance rejection controller is designed in a rotating speed loop, an improved LESO is designed by constructing a state observation error differential term and a coefficient thereof, an integral + differential parallel structure is constructed in a signal transmission path for estimating total disturbance of the rotating speed loop, and the medium-high frequency disturbance tracking speed is increased by using the phase lead characteristic of the differential term. And by combining a second-order IIR Butterworth high-pass filter, high-frequency noise introduced due to the increase of the bandwidth of the observer can be accurately separated and filtered out, the inherent contradiction between bandwidth improvement and noise amplification in the traditional LADRC is broken through, and the improvement of the rotation speed fluctuation suppression ratio under the low-speed working condition is realized. Model-free predictive control is adopted in a current loop, dependence of a system on accurate modeling of motor parameters is reduced, current tracking errors generated under the condition of parameter mismatch are reduced, torque pulsation caused by current fluctuation is reduced, and then rotating speed fluctuation is reduced.

The invention relates to a double-branch reconstruction type image anomaly detection method for industrial quality inspection, and belongs to the field of anomaly detection. The method comprises the following steps: 1) carrying out pseudo-anomaly synthesis on an original industrial image, and constructing a training sample containing anomaly features; 2) adopting a pre-trained feature extraction network to perform feature extraction on the pseudo abnormal samples and the normal samples; 3) using a Butterworth high-pass filter to extract a high-frequency component of the pseudo abnormal sample; 4) constructing a double-branch reconstruction network, respectively reconstructing the pseudo-abnormal features and the high-frequency components, and realizing feature alignment and reconstruction of pseudo-abnormal data by taking normal sample feature distribution as a target; and 5) verifying the effectiveness of the proposed method in an anomaly detection task through a comparison experiment with a plurality of existing methods. The innovation point of the invention lies in providing a new pseudo-abnormal data generation mechanism, designing a space and high-frequency double-branch reconstruction network, and significantly improving the detection capability of structural and logic anomalies in industrial quality inspection.

A vehicle includes a suspension system having a damping system that includes a plurality of dampers and a plurality of damper valves. The vehicle further includes one or more processors configured to determine energy content of an acceleration signal indicative of acceleration of the vehicle. The one or more processors are further configured to dynamically tune a cutoff frequency of a high-pass filter based on the energy content of the acceleration signal. The one or more processors are configured to filter, via the high-pass filter, a velocity signal derived from the acceleration signal to output a filtered velocity signal. The one or more processors are configured to control operation of the damping system based on the filtered velocity signal.

The invention relates to the technical field of control of a hybrid energy storage system of a direct-current optical storage overcharge station, and provides a double-layer fuzzy dynamic power distribution control method of a hybrid energy storage system, which comprises the following steps of: performing combined optimization by taking a direct-current bus reference current Idcref, a super capacitor state SOCsc and a storage battery state SOCbat as input; a first-layer fuzzy controller is constructed to dynamically adjust a filtering time constant T to serve as a parameter of a high-pass filter, and an initial power distribution instruction is generated; constructing a second-layer fuzzy controller to dynamically adjust the super capacitor protection state instruction Isc; and finally, based on the data obtained in the above process, adjusting the output reference current of the hybrid energy storage battery and the output reference current of the super capacitor in real time. According to the method, the charge states of the storage battery and the super capacitor are comprehensively considered at the same time to dynamically distribute the power, and the economical efficiency and the safety of operation of the hybrid energy storage system are improved.

An integrated triggering system for a pulsed-power driver is presented. The triggering system includes a pulse distribution circuit that couples externally generated trigger pulses to midplanes of a limited number of stages of the pulsed-power driver. The pulse distribution circuit includes common midplane nodes, each coupled to a group of midplanes of a same stage via respective isolating inductors. Isolating elements are coupled between the common midplane nodes of a same stage. The triggering system further includes a protection circuit configured to reduce coupling of high voltages triggered at the midplanes to external circuits while allowing the trigger pulses to couple to the midplanes. The protection circuit includes a high pass filter comprising a capacitor. The triggering system further includes a midplane biasing circuit configured to provide a reference ground to the midplanes of all stages. The midplane biasing circuit includes a resistive ladder with nodes coupled to the midplanes.

An interface circuit configured in accordance with certain aspects of this disclosure has a high-pass filter and a low-pass filter. The high-pass filter may include a capacitor coupled between an input of the interface circuit and an output of the interface circuit and a resistor coupled between the output of the interface circuit and a voltage reference source. The capacitor and resistor may be configured to provide a low-pass filter that couples the reference voltage source to the output of the interface circuit. The interface circuit provides a feedforward loop that includes the reference voltage source and an amplifier. The amplifier has an input coupled to the input of the interface circuit and an output coupled to the reference voltage source.

The invention provides a network construction type converter fault ride-through control method based on model predictive control and a resonance controller, and the method comprises the following steps: A, obtaining a reference value of power under a fault according to a network construction type converter and a virtual synchronous generator (VSG) mathematical model with the purpose of providing required positive sequence reactive power; step B, extracting a fault transient component through a high-pass filter and generating a capacitor voltage positive sequence reference value by using a resonance controller; step C, selecting different capacitor voltage negative sequence reference values according to different control targets; step D, obtaining a filtering current reference value through the reference values of the positive sequence capacitor voltage and the negative sequence capacitor voltage, and constructing a cost function containing current amplitude limiting; and selecting an optimal voltage vector. Compared with the existing method, the method has the advantages that the transient suppression is faster, the steady-state current is not influenced, the resonant controller specifically suppresses a 50Hz transient component, and the reactive response speed is improved by 43% compared with that of a virtual impedance method.

The application discloses a kind of LCL grid-connected current feedback active damping control method and system, belong to power filter control technical field, including the grid-connected current i2 of the acquisition inverter net side;Grid-connected current i2 flows through negative low-pass-high-pass filter and is handled, obtains feedback current;Feedback current and the output of inverter current controller are superposed, as the control signal of LCL filter.The application will not amplify high-frequency harmonic current, and the control system still has good robustness when LCL filter parameter changes.

The application discloses a local discharge signal processing method and device under high-frequency square wave voltage, wherein the method comprises the following steps: filtering low-frequency noise signals of a test power supply by using a high-pass filter with a preset cutoff frequency, wherein the test power supply is a high-frequency square wave power supply for local discharge test of an insulation sample; obtaining a local discharge starting voltage of the insulation sample, collecting a local discharge signal when a test voltage is the local discharge starting voltage, obtaining a characteristic frequency band of local discharge of the insulation sample according to the local discharge signal, and the test voltage is a high-frequency square wave voltage of the test power supply; performing modal decomposition on the local discharge signal of the characteristic frequency band to obtain a plurality of modal components, selecting a plurality of modal components satisfying a preset condition to perform noise reduction processing and signal reconstruction, and obtaining a denoised local discharge signal of the insulation sample under the high-frequency square wave voltage. The application can avoid interference of the high-frequency square wave power supply on the local discharge signal, and obtain a local discharge signal with high signal-to-noise ratio under the high-frequency square wave voltage.

To provide a partial discharge measuring device and partial discharge determination method for AC rotating electric machines that are inexpensive, do not require modification work on existing equipment, and have a low risk of accidents. [Solution] The partial discharge measuring device 1 according to the present invention measures partial discharge occurring in an AC rotating electric machine 3, and is characterized by comprising: a metal foil electrode 5 of a predetermined area attached to the outer surface of the power main cable 13 within 1 m from the end of the lead wire 11 of the AC rotating electric machine 3; a circuit 7 with one end connected to the metal foil electrode 5 and grounded via a detection resistor 25; and a partial discharge measuring device 9 that measures the voltage signal caused by the partial discharge occurring at both ends of the detection resistor 25 by inputting it via a high-pass filter 27.

The present invention discloses a multi-sensitivity composite vibration sensor and a separation method thereof. The composite vibration sensor includes a preamplifier and a signal separation unit. The preamplifier includes an access identification circuit, an analog switch, a microcontroller (MCU), an anti-reverse and interface protection module, and a signal acquisition unit. The signal acquisition unit is connected to the access identification circuit, then to the analog switch, then to the microcontroller (MCU), and finally to the anti-reverse and interface protection module. The signal separation unit includes a low-pass filter, a high-pass filter, a low-pass signal processor, a high-pass signal processor, an ADC (ADC) anti-aliasing, and an analog-to-digital converter (ADC). The low-pass or high-pass filter is connected to the anti-reverse and interface protection module. After the low-pass filter is connected to the low-pass signal processor, and after the high-pass filter is connected to the high-pass signal processor, both are connected to the ADC anti-aliasing. The ADC anti-aliasing is connected to the analog-to-digital converter (ADC). The sensor can obtain multiple sensitivities, so that the required signal has an appropriate sensitivity and a suitable signal-to-noise ratio is achieved during transmission.

The application relates to the field of high-pass filters, and relates to a high-pass filter processing device and a swing processing platform. The high-pass filter processing device comprises a base and a glue injection mechanism, the base is fixedly connected with a supporting column, the supporting column is slidably installed with a supporting plate, the glue injection mechanism comprises a glue storage bin fixedly connected with the base and a glue outlet pipe fixedly connected with the supporting plate; the glue storage bin and the glue outlet pipe are connected through a pipeline, the bottom of the glue outlet pipe is installed with a first glue outlet head, the supporting plate is installed with a conversion component, the first glue outlet head is connected with the conversion component, the conversion component is installed with a second glue outlet head which can also be connected with the glue outlet pipe; the high-pass filter swing processing platform comprises the high-pass filter processing device and a supporting table fixedly connected with the base, the supporting table is rotatably installed with a rotating disc, the rotating disc is installed with multiple groups of clamping components for fixing the filter. The application improves the problem of low processing efficiency of the filter.

The invention discloses a jitter suppression method and system for an AGV. The method comprises the steps that a rotor speed signal and a torque instruction signal of a permanent magnet synchronous motor of the AGV are collected; performing discretization sampling on the rotor speed signal to obtain a discrete speed signal; performing spectral analysis on the discrete speed signal to extract a corresponding vibration spectrum, and obtaining a main frequency point where resonance occurs; inputting the discrete speed signal into a high-pass filter to extract a component required by active damping suppression of a vibration frequency point, carrying out discretization differential on the discrete speed signal to obtain an acceleration signal, and carrying out band-pass filtering on the acceleration signal by adopting a band-pass filter to obtain a component required by acceleration feedback suppression; the cut-off frequency of the high-pass filter and the center frequency and bandwidth of the band-pass filter are determined by main frequency points; and a compensation torque signal is obtained according to the jitter component and the component required for acceleration feedback suppression, so that jitter caused by resonance of the AGV is suppressed according to the compensation torque signal.

Systems, apparatuses, and methods for performing efficient data transfer in a computing system are disclosed. A computing system includes multiple transmitters sending singled-ended data signals to multiple receivers. In order to better handle noise issues when using single-ended signaling, one or more of the receivers include equalization circuitry and termination circuitry. The termination circuitry prevents reflection on a corresponding transmission line ending at a corresponding receiver. The equalization circuitry uses a bridged T-coil circuit to provide continuous time linear equalization (CTLE) with no feedback loop. The equalization circuitry performs equalization by providing a high-pass filter that offsets the low-pass characteristics of a corresponding transmission line. A comparator of the receiver receives the input signal and compares it to a reference voltage. The placement of the comparator and the ratio of the inductances of the inductors of the bridged T-coil circuit are based on whether the receiver includes self-diagnostic circuitry.

A protection device against pulsed currents intended to transmit signals having frequencies lying in a transmission frequency band. The protection device has a signal conduction path and a shielding disposed around the signal conduction path. The signal conduction path has two spark gaps mounted in series and an inductor element linking a portion of the signal conduction path situated between the spark gaps. The inductor element is linked to the shielding. The protection device is configured as a high-pass filter allowing passage over the signal conduction path of the signals having frequencies lying within the transmission frequency band.

There is disclosed herein a method (100) for sub-synchronous damping control, SSDC, for a STATCOM (20) connected to an alternating current, AC, power grid (2). The method comprises measuring (110) a voltage representative of the voltage of the AC power grid and subjecting (120) the voltage to a low-pass filter and a high-pass filter. The method further comprises cross-coupling (130) an active power order of the voltage with a reactive power decoupler parameter of the voltage to receive a voltage phase angle parameter and cross-coupling a reactive power order of the voltage with an active power decoupler parameter of the voltage to receive a voltage magnitude parameter, and combining (140) the voltage phase angle parameter and the voltage magnitude parameter to provide a voltage reference to the STATCOM. There is also disclosed herein a converter for a STATCOM and a system comprising a STATCOM and said controller.

This invention belongs to the technical field of information technology, specifically disclosing a method and system for AGC load allocation in hydropower stations considering vibration risk. The method includes: acquiring real-time tilt angle time-series data of the unit bearing housing and guide vane support; processing the real-time tilt angle time-series data using preset high-pass and low-pass filters; the high-pass filter output representing rapid fluctuation components changing from seconds to minutes, and the low-pass filter output representing slow drift components changing from hours to days; calculating the transient vibration impact index and the long-term structural degradation index based on the amplitude characteristics of the rapid fluctuation components and the cumulative trend of the slow drift components, respectively; the transient vibration impact index reflecting the instantaneous mechanical stress level caused by the current load adjustment; the purpose of this invention is to solve the problem in the prior art of how to simultaneously identify and weigh the transient vibration risk caused by rapid tilt angle changes and the long-term structural degradation risk caused by slow tilt angle drift in load allocation decisions.

The application discloses a kind of virtual synchronous generator transient damping control methods based on state observation, comprising the following steps: step S1: the original rotor motion equation of VSG is constructed, and equivalent transient unbalance torque item is acted on the virtual shaft of VSG, the augmented dynamic model of VSG is obtained, and augmented state space equation is constructed;Step S2: the state vector of the state observer of classic Luenberger is estimated and corrected using Luenberger state observer combined with the measurable output of VSG model, and the recursive formula under the sampling period of step S2 is given;Step S3: the comprehensive feedforward compensation link containing high-pass filter is introduced, and strong active damping is provided in transient oscillation frequency band, combined with the recursive formula in step S2, the transient damping control of virtual synchronous generator under frequency band isolation is realized. T s The application provides strong transient active damping for system without increasing the order of main control system, effectively avoiding high-frequency noise amplification, and completely cutting off the interference to steady-state channel.

A kind of SINS self-aided navigation method based on maneuvering constraint and incremental filtering, 1 drives AUV to do periodic steady motion in horizontal direction, while maneuvering to specified direction, adds high-frequency component to the velocity in navigation coordinate system;2 obtains real-time data of inertial sensor installed on underwater AUV;3 input the horizontal velocity in navigation coordinate system obtained in step 2 into high-pass filter, obtains a set of horizontal velocity in navigation coordinate system with low-frequency error component removed;4 establishes Kalman filter, the increment of velocity component obtained in step 3 is input into Kalman filter as the measurement of Kalman filter, the obtained velocity error is compensated, and high-precision positioning value after self-aided compensation is obtained.The application effectively solves the problem that SINS positioning error diverges with time, compared with the positioning scheme of pure SINS solution, the velocity error can be limited in a very small range, and the positioning accuracy is greatly improved.

The utility model relates to a pole switch with integrated coupler and capacitive voltage sensor, including, first electric capacity CH is connected with power A, and second electric capacity CL is connected with first electric capacity CH, one input of high pass filter and low pass filter is connected with one end of second electric capacity CL respectively, the output of high pass filter is connected signal coupler, the utility model promotes long -term reliability and measurement accuracy: in traditional scheme, because voltage sensor and communication coupler are separate, are easily affected by outside environment and lead to system unreliable or measurement inaccuracy. And the utility model through adopting low pass filter isolation high frequency signal ensures voltage sensor normal work, and uses high pass filter to guarantee signal coupler normal operation, effectively prevented high frequency communication signal to voltage sampling loop's crosstalk and strong power frequency voltage to coupler's damage, improved the long -term reliability and voltage measurement accuracy of system.

According to some embodiments, a receiver comprises a positive terminal, a negative terminal, a first isolation capacitor connected to the positive terminal, a second isolation capacitor connected to the negative terminal, a resistor circuit connected to the first isolation capacitor and the second isolation capacitor to define a first high pass filter, an amplifier connected to the first high pass filter, a level detector connected to the amplifier, and a second high pass filter connected between the first high pass filter and the level detector.