Frequency Measurement Method Research Articles

The resonant frequency measurement method for superconducting cavity with Lorentz force detuning

The precise measurement of resonance frequency is very important to tune the cavity and stabilize the RF field. The minimal-reflection method is usually used to measure the cavity resonance frequency, but the accuracy may not meet the stability requirement for the superconducting cavity with narrow bandwidth. The falling-edge method with high precision has been used for the resonance frequency measurement of the normal conducting cavity, but it cannot be used directly for the superconducting cavity due to the effect of Lorentz Force Detuning (LFD). This paper presents the solution for applying the falling-edge method to measure the resonance frequency of superconducting cavity with LFD. The periodic iteration algorithm is developed to calculate the frequency detuning and phase shift caused by the dynamic Lorentz Force within RF falling-edge. The phase shift due to the deviation of initial resonance frequency is derived by subtracting the LFD item from the phase measurement, and the initial resonance frequency can be determined finally. The method has been tested on the superconducting cavity at CAFE facility, and the effectiveness has been demonstrated.

High-precision frequency measurement for microresonant sensors based on improved modified multi-phase clock method.

Microelectromechanical system resonant sensors are widely used in high precision applications. Frequency measurement plays an important role in such frequency readout sensors. This paper proposed an improved modified frequency measurement method based on the multi-phase clock (MPC), which can effectively improve the measurement accuracy but does not reduce the output rate. Innovative claims include (1) building a model of measurement error for MPC in which the probability of triggering error under different conditions is calculated, (2) improving the accuracy of the MPC measurement by phase reverse, and (3) proposing an algorithm to eliminate jitters of the measured signal. We compared the measurement results of this optimized MPC realized by the field programmable gate array (FPGA) device with those of the conventional MPC, spectral measurement, and equal precision measurement implemented with the National Instruments acquisition equipment PXI-4461 and USB-6366, respectively. The results show that the bias instability of the adopted method is ∼10 µHz obtained by Allan variance analysis, which is better than that of the other three methods. It can meet the accuracy requirements for the resonant frequency measurement of state-of-the-art resonant accelerometers. In addition, an algorithm running in FPGA is proposed to eliminate jitters caused by the noise of the measured signal for enhancing the robust of optimized MPC. The results demonstrate that the optimized MPC has features of high accuracy and anti-interference capability and can be easily transferred to the application specific integrated circuit in the future due to its full digital circuit version.

High-precision nuclear-quadrupole-resonance thermometer for aerohydrodynamic research

In hydroaerodynamics, there are problems that require increased accuracy of temperature measurement. An example is the measurement of excess temperature at the periphery of turbulent jets. Unlimited temperature increase on the axis of the jet to increase the accuracy of measurement is impractical due to non-automodeliness by the Archimedes number. To do this, it is possible to use the phenomenon of nuclear quadrupole resonance. The device for exact measurement of temperature in the range from 0° C to +200 °C is offered. Using the LabView graphic programming package, a virtual model of an automatic thermometer based on nuclear quadrupole resonance in КClO3 was built. The temperature sensor is a superregenerative spectrometer with automatic monitoring of the center of the absorption line of the thermometric substance, consisting of the actual superregenerator, bandpass filter, comparator, DC amplifier and modulating voltage generator. The circuit that switches the supergenerator to the mode of continuous generation and output of information on the display contains a single vibrator, a buffer stage, a microcontroller and an indicator. From the output of the superregenerator, the absorption signal is fed to the bandpass filter, and then to the comparator. After the comparator, a voltage equal to the input voltage difference is amplified by a DC amplifier. This signal controls the resonant absorption frequency through the feedback circuit. The frequency of the sensor polling is determined by a single vibrator, the oscillations of which are synchronized with the clock generator. Measuring uncertainty in the range above changes from 0.02 K to 0.002 K It has been shown that either a manual frequency measurement method or a regenerative mode must be used to reduce the measurement uncertainty up to 0.002 K in the range. This improved automatic device is more complex, because of requirements of special measures to eliminate parasitic amplitude modulation. To increase the temperature range and precision, it is possible to find other thermometric substance, such as Сu2O crystals.

A Frequency Measurement Algorithm for Power Quality Monitoring Terminal

With the continuous access of high-power electronic equipment, electric vehicles and other loads in the user side, the frequency of power grid fluctuates. As one of the power quality parameters, higher or lower frequency has a negative impact on power system and users. Therefore, the accurate measurement of frequency is of great significance to the State Grid and users. In order to measure the frequency accurately, this paper proposes a frequency measurement method according to power quality monitoring technical specifications issued by the State Grid in 2017. Through the design of band-pass filter to filter out DC (Direct Current) component and high-frequency harmonic interference, along with the improved zero-crossing detection process, aim to judge the whole cycle wave number and its occupation time in ten-second time interval. Matlab is used to simulate the accuracy of the algorithm under different conditions. The results show that the error range measurement of frequency is far less than the accuracy level of class A and S power quality testing equipment. Therefore, this algorithm is feasible in the application of power quality monitoring terminal.

A frequency measurement method using rising-falling edge of square wave for increasing proton magnetometer precision

To improve the measurement precision of the proton magnetometer (PM), a multi-average multi-cycle frequency measurement (M-MFM) method using both rising and falling edge of square wave is proposed in this study. First, the M-MFM method using Rising-Falling edge of square wave is presented based on the multi-cycle frequency measurement (MFM) method, and the formula of frequency measurement is deduced. Then, the relative error of the proposed method is analyzed, and the proposed method is optimized by solving the minimum value of the relative error formula. Finally, the implementation process of the proposed method in STM32 is introduced. The experimental results of the frequency measurement demonstrate that the measurement precision for low SNR sine signals is significantly increased by the proposed method. The experimental results of the magnetic field measurement show that the sensitivity is about 0.11 nT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> @0.25 Hz in the range of the geomagnetic field while the proposed method is adopted by the PM, which is better than that of the other methods and the commercial instruments.

Lock-in frequency measurement with high precision and efficiency.

This paper describes a new method of frequency measurement based on lock-in amplifiers (LIAs). In contrast to other frequency measurement methods, such as fast Fourier transformation (FFT), zero crossing, and scanning autocorrelation, this method is based on an adaptable LIA design for high-precision determination of not only the frequency but also the amplitude and phase of periodic signals, even when they are buried in heavy noise with low signal-to-noise ratios. Mathematical derivation of the local spectrum around the center frequency is performed, and the local frequency spectrum waveform of the sinusoidal signal, regardless of whether it is pure or noisy, is found to be exactly of a bell shape that can be described by a three-parameter sine function. Based on the principle of LIAs, the correct frequency can produce a peak amplitude in the local spectrum. As a result, the amplitudes of three frequency points around the target frequency can be used to precisely determine the peak frequency via sinusoidal fitting. The efficiency of the proposed method is log2(N) times that of FFT. Simulation results show that the new algorithm can reach the theoretical Cramer-Rao lower bound and remain below a lock-in upper bound. The new frequency measurement method has been implemented in an field-programmable gate array (FPGA)-based device and systematically tested for its dependence on the frequency, amplitude, and signal-to-noise ratio with typical noise types. Theoretical and experimental results show that the new method can be used in fine determination of the frequency if the user has prior knowledge of the approximate location of the frequency.

동기발전기 위상각 안정도 향상을 위한 에너지저장장치(GS-ESS) 적용에 관한 연구

For various reasons, the power system stability margin is continuously decreasing. However, in case of Korea, the expansion of the transmission system is facing difficulties due to worsening social acceptability. As an alternative, a technology to increase the power system stability margin using some converter-based facilities is being proposed. In this paper, GS-ESS(Generator Stabilization Energy Storage System) was proposed as a measure to improve the angular stability of synchronous generator. To overcome the limitations of typical ESS frequency measurement methods(using PLLs), GS-ESS directly measures the rotational speed of the generator mechanically and converts it into an electrical signal.<BR>In this case study, PSS/E simulation has been performed to analyze the effect of GS-ESS application. For this simulation, we used the 21 buses test system and GS-ESS was installed in the plant bus. And then we analyzed the effects of improving stability according to capacity and response speed in case of fault on the interconnection line between generator and power system. As a result, this case study showed that GS-ESS can be contributed to improving the angular stability of the synchronous generator.

A Self-adaptive and Self-Sufficient Energy Harvesting System.

Self-adaptive vibration energy harvesters convert the kinetic energy from vibration sources into electrical energy and continuously adapt their resonance frequency to the vibration frequency. Only when the two frequencies match can the system harvest energy efficiently. The harvesting of vibration sources with a time-variant frequency therefore requires self-adaptive vibration harvesting systems without human intervention. This work presents a self-adaptive energy harvesting system that works completely self-sufficiently. Using magnetic forces, the axial load on a bending beam is changed and thus the resonance frequency is set. The system achieves a relative tuning range of 23% at a center frequency of 36.4 Hz. Within this range, the resonance frequency of the harvester can be set continuously and precisely. With a novel optimized method for frequency measurement and with customized electronics, the system only needs 22 µW to monitor the external vibration frequency and is therefore also suitable for environments with low vibration amplitudes. The system was verified on a vibrational test bench and can easily be tailored to a specific vibration source.

A broad range frequency measurement method for continuous and pulsed THz waves.

This paper proposes a method to measure the frequency of terahertz (THz) waves based on the Zeeman effect and the high magnetic field technology with a wideband range from 60 GHz to 3 THz. As the frequency of THz waves absorbed by the sample is linear to the magnetic field in the Zeeman effect, the frequency can be measured by the magnetic field strength. A comparison study of THz frequency measurement was carried out in two magnet systems (a superconducting one and a pulsed one) to investigate the performance in two kinds of high magnetic fields. The experimental results of 60-700 GHz show that this method has high resolution (about 0.001%), excellent linearity, and good repeatability. Moreover, the proposed method can measure polychromatic signals simultaneously as well as the single pulse frequency in the order of tens of microseconds.

A Novel Three-Point Windowed Interpolation DFT Method for Frequency Measurement of Real Sinusoid Signal

A Novel Three-Point Windowed Interpolation DFT Method for Frequency Measurement of Real Sinusoid Signal

A multiple microwave frequency measurement based on stimulated Brillouin scattering in few-mode optical fiber

Abstract A novel multiple microwave frequency measurement method is proposed. The operational principle is based on stimulated Brillouin scattering (SBS) in few-mode fiber (FMF). Due to the existence of SBS between the different modes of FMF, there are several different Brillouin frequency shifts in the fiber. Thus, a microwave frequency can be measured using an existing technique; even if the difference in the unknown frequencies is twice that of one of the Brillouin frequency shifts, the frequencies can be distinguished from the acquired signal powers of different ports of a mode-division multiplexer.

Real-Time Direct Measurement Method of Power System Frequency

Accurate measurement of grid frequency timely is essential to the stable operation of a grid network and the performance of a grid-connected converter. When harmonic pollution exists in the power system, indexes of timeliness, accuracy, and noise rejection performance are required to be considered synthetically. However, these indexes are usually difficult to be taken care of at the same time, and problems of convergence and stability should also be considered. In order to calculate grid frequency precisely and timely, this paper proposes a grid frequency measurement method. A three-level function of the grid voltage signal is defined step by step. On the basis of the function, equations with the signal's frequency and amplitude as two unknowns are established. Finally, a system of equations is obtained and solved in order to calculate grid frequency. The proposed method calculates grid frequency precisely through strict theoretical derivation, possesses a strong anti-disturbance ability against harmonics, and is simple for realization. In addition, because of the absence of iteration and feedback calculation, problems of convergence property as well as stability do not exist. Effectiveness of this method is proved through simulation and experiment.

Wide-range, high-accuracy multiple microwave frequency measurement by frequency-to-phase-slope mapping

A photonics-based method of instantaneous frequency measurement (IFM) based on Stimulated Brillouin scattering (SBS) is proposed and theoretically analyzed. The principle of the technique is the employment of the Brillouin gain-loss compensation and monotonous frequency-to-phase-slope mapping (FTPSM) method, where the FTPSM is realized utilizing the correlation between Brillouin phase shift and unknown signal frequency. With the new technique, the frequency of a signal and multiple unknown RF signal can be measured and due to bypass a fundamental trade-off between measurement range and accuracy through our method, resulting in the measurement range of the system is extended from 2VB to 4VB with a higher accuracy ~4 MHz. In addition, the influences of the pump light wavelength variation and power change on the performance of the IFM system are discussed.

On-chip two-step microwave frequency measurement with high accuracy and ultra-wide bandwidth using add-drop micro-disk resonators.

An on-chip two-step microwave frequency measurement method with high accuracy and an ultra-wide frequency measurement range is reported. A silicon photonic integrated micro-disk resonator (MDR) array is used to coarsely measure the signal frequency via an array of add-drop MDRs with smaller disk radii; then an MDR with a larger radius is used to finely measure the signal frequency, which is done by monitoring the optical powers of the optical signals from the through port and drop port of the MDRs. The proposed system features a very compact structure, ultra-wide frequency measurement range, and high frequency measurement accuracy, which is verified by a proof-of-concept experiment using two MDRs with radii of 6 and 10μm. A frequency measurement of microwave signals from 1.6 to 40GHz is implemented with a measurement error of less than 60MHz. The stability of the system is also evaluated.

Validations of simulation of UHF electromagnetic wave propagation in an oil‐filled tank by time‐domain measurements

Degradation of the electrical insulation within power transformers by partial discharge (PD) may lead to catastrophic failure of the apparatus, hence PD should be detected at an early stage. Ultra-high frequency (UHF) measurement method, i.e. detecting electromagnetic (EM) waves in the UHF range radiated from PD, has recently received attention for its various advantages, such as the robustness against external noises and its capability of localisation of the PD position. However, the EM waves suffer attenuation while propagating within transformers, in some cases, which results in undesirable low detection sensitivity. To evaluate the propagation and attenuation characteristics of the EM waves quantitatively, the simulation technique of the EM wave propagation is of importance. In this study, at first, the EM waveforms as well as attenuation properties of their amplitudes and cumulative energies while propagating through transformer windings in an oil-filled tank were experimentally investigated. Next, the detailed conditions for simulating the EM wave propagation based on time-domain finite integration technique were described. Then, the simulated results were compared with the experimentally obtained ones. These simulation and measurement results showed good agreement with each other, therefore the authors have successfully validated the newly developed simulation of the EM wave propagation.

A precise resonance frequency measurement method based on ISO‐standardized setups for contactless chip cards

A precise resonance frequency measurement method based on ISO‐standardized setups for contactless chip cards

Photonics-Based Broadband Microwave Instantaneous Frequency Measurement by Frequency-to-Phase-Slope Mapping

A photonics-based broadband microwave instantaneous frequency measurement (IFM) method is proposed by monotonously mapping the frequency to the slope of the time-varying phase of the microwave signal under test. This frequency-to-phase-slope mapping approach is realized utilizing a variable photonic delay line and a microwave photonic in-phase/quadrature (I/Q) mixer, where the I/Q mixer is composed of two phase modulators connected tail to tail within a fiber loop, an optical 90° hybrid, and a pair of low-speed balanced photodiodes. Thanks to the monotonous frequency-to-phase-slope mapping property, as well as the use of photonic delay line and microwave photonic I/Q mixing, the IFM system can achieve a wide-range frequency measurement without ambiguity. An experiment is performed. The established IFM system is able to operate from 5 to 67 GHz with a measurement error of less than 500 MHz, which achieves the widest frequency measurement range ever recorded by photonics-based IFM systems. In addition, the influences of the I/Q phase mismatch and the amplitude noise on the performance of the IFM system are also discussed. We believe that this photonics-based IFM system is a promising solution for wideband microwave frequency measurements.

A study on dynamic measurement methods based on vibrating wire sensors

Vibrating wire sensors are widely used in long-term static strain monitoring. However, when dynamic measurements are needed, conventional measuring methods are unsuitable. On the basis of the static measuring method, in this paper we propose a new method of dynamic frequency excitation and measurement based on vibrating wire sensors. In the dynamic frequency excitation method, we adopt intermittent self-adaptive excitation which allows the internal steel in the sensor to vibrate continuously, without attenuation. In turn, this allows us to continuously collect and analyze the sensor signal. We use a dynamic frequency measurement algorithm to subsequently process the data, which interpolates three spectral lines based on a windowed fast Fourier transform. The resonance frequency of the sensor is obtained, which then allows us to dynamically acquire the strain. Through data analysis, the theoretical calculation error of the resonance frequency can be obtained to within 0.015 Hz, and the theoretical sampling rate of dynamic strain measurement can reach to 325 Hz. In addition, through our experiments, the efficiency and the feasibility of our methods are verified.

Large‐scale source‐grid‐load friendly interactive system introduction and real load shedding verification test technology

On the basis of briefly analysing the construction background, systemic function, and practice situation of large-scale source-grid load friendly interactive system and introducing real load shedding verification of the system, this paper proposed an effective strategy validation technique based on preset instruction release mode, a time test method of real load shedding control command transmission according to global GPS clock synchronisation technology, and a frequency measurement method according to zero-crossing detection and digital filter technology. These methods can accurately measure the system's control time and dynamic frequency on real load shedding. The real experimental results verified that quick load shedding time and frequency control effect when DC-blocking fault happens meet system expectations. It effectively verified the function design of large-scale source-grid-load friendly interactive system.

Метод измерения частоты основного тона речевого сигнала для систем акустического анализа речи

Метод измерения частоты основного тона речевого сигнала для систем акустического анализа речи