Zero-crossing Point Research Articles

Simultaneous Estimation of Ofloxacin, Clotrimazole, and Lignocaine Hydrochloride in Their Combined Ear-Drop Formulation by Two Spectrophotometric Methods.

Two sensitive, accurate, and precise spectrophotometric methods have been developed and validated for the simultaneous estimation of ofloxacin (OFX), clotrimazole (CLZ), and lignocaine hydrochloride (LGN) in their combined dosage form (ear drops) without prior separation. The derivative ratio spectra method (method 1) includes the measurement of OFX and CLZ at zero-crossing points (ZCPs) of each other obtained from the ratio derivative spectra using standard LGN as a divisor, whereas the measurement of LGN at the ZCP of CLZ is obtained from the ratio derivative spectra using standard OFX as a divisor. The double divisor-ratio derivative method (method 2) includes the measurement of each drug at its amplitude in the double divisor-ratio spectra obtained using a standard mixture of the other two drugs as the divisor. Both methods were found to be linear (correlation coefficients of >0.996) over the ranges of 3-15, 10-50, and 20-100 μg/mL for OFX, CLZ, and LGN, respectively; precise (RSD of <2%); and accurate (recovery of >98%) for the estimation of each drug. The developed methods were successfully applied for the estimation of these drugs in a marketed ear-drop formulation. Excipients and other ingredients did not interfere with the estimation of these drugs. Both methods were statistically compared using the t-test.

A pulse-width modulation technique for BLDC motor drive system to reduce commutation time

Commutations occurring in brushless DC motor (BLDCM) drive system cause failure of a sensorless drive based on zero-crossing detection of back-electromotive force (BEMF) when the commutation angle reaches or exceeds 30°. On the other hand, increasing the load on the motor slows down falling process of outgoing phase current during commutation. This paper presents a new method for complete vanishing of outgoing phase current before BEMF zero-crossing point, using a pulse-width modulation (PWM) mode in which an adaptive pattern is inserted to H-PWM_L-ON mode synchronously with commutation time. The proposed PWM mode can be used for sensorless drive based on direct BEMF zero-crossing detection method. The proposed method is applied to a 14 kW/220 V BLDCM with constant v/f control, and the results show that as the duty cycle of PWM is reduced, commutation time becomes shorter and the transferred power to motor is increased compared to H-PWM_L-ON mode.

Self-Correction of Commutation Point for High-Speed Sensorless BLDC Motor With Low Inductance and Nonideal Back EMF

This paper presents a novel self-correction method of commutation point for high-speed sensorless brushless dc motors with low inductance and nonideal back electromotive force (EMF) in order to achieve low steady-state loss of magnetically suspended control moment gyro. The commutation point before correction is obtained by detecting the phase of EMF zero-crossing point and then delaying 30 electrical degrees. Since the speed variation is small between adjacent commutation points, the difference of the nonenergized phase's terminal voltage between the beginning and the end of commutation is mainly related to the commutation error. A novel control method based on model-free adaptive control is proposed, and the delay degree is corrected by the controller in real time. Both the simulation and experimental results show that the proposed correction method can achieve ideal commutation effect within the entire operating speed range.

A 2 GSps, 8-Bit Folding and Interpolation ADC with Foreground Calibration in 90 nm CMOS Technology

A single channel 2 GSps, 8-bit folding and interpolation (F&amp;I) analog-to-digital converter (ADC) with foreground calibration in TSMC 90 nm CMOS technology is presented in this paper. The ADC utilizes cascaded folding, which incorporates an interstage sample-and-hold amplifier between the two stages of folding circuits to enhance the quantization time. A master-slave track-and-hold amplifier (THA) with bootstrapped switch is taken as the front-end circuit to improve ADC’s performance. The foreground digital assisted calibration has also been employed to correct the error of zero-crossing point caused by the circuit offset, thus improving the linearity of the ADC. Chip area of the whole ADC including pads is 930 μm × 930 μm. Postsimulation results demonstrate that, under a single supply of 1.2 volts, the power consumption is 210 mW. For the sampling rate of 2 GSps, the signal to noise and distortion ratio (SNDR) is 45.93 dB for Nyquist input signal.

Implementation of a MFAC based position sensorless drive for high speed BLDC motors with nonideal back EMF

In order to improve the reliability and reduce power consumption of the high speed BLDC motor system, this paper presents a model free adaptive control (MFAC) based position sensorless drive with only a dc-link current sensor. The initial commutation points are obtained by detecting the phase of EMF zero-crossing point and then delaying 30 electrical degrees. According to the commutation error caused by the low pass filter (LPF) and other factors, the relationship between commutation error angle and dc-link current is analyzed, a corresponding MFAC based control method is proposed, and the commutation error can be corrected by the controller in real time. Both the simulation and experimental results show that the proposed correction method can achieve ideal commutation effect within the entire operating speed range.

Arc flash fault detection in wind farm collection feeders based on current waveform analysis

High impedance faults (HIFs) are easy to occur in collective feeders in wind farms and may cause the cascading of wind generators tripping. This kind of faults is difficult to be detected by traditional relay or fuse due to the limited fault current values and the situation is worse in wind farms. The mostly adopted HIF detection algorithms are based on the 3rd harmonic characteristic of the fault zero-sequence currents, whereas these 3rd harmonics are very easy to be polluted by wind power back-to-back converters. In response to this problem, the typical harmonic characteristic of HIF arc flash based on Mayr’s arc model is first analyzed, and the typical fault waveforms of HIF in wind farm are presented. Then the performance of the harmonic based HIF detection algorithm is discussed, and a novel detection algorithm is proposed from the viewpoint of time domain, focusing on the convex and concave characteristic of zero-sequence current at zero-crossing points. A HIFs detection (HIFD) prototype implementing the proposed algorithm has been developed. The sensitivity and security of the algorithm are proved by field data and RTDS experiments.

Detection of rice phenology through time series analysis of ground-based spectral index data

Monitoring crop phenology is of great importance for vegetation classification, yield estimation, and irrigation and fertilization management. To test the ability of ground-based remote sensing in detecting major phenological dates of rice, canopy spectra were collected by two portable spectrometers. The Red-edge Chlorophyll Index (CIred edge) and Normalized Difference Vegetation Index (NDVI) time-series derived from ground-based spectrometers were employed to detect the main specific phenological dates. CIred edge was obtained from ASD FieldSpec Pro spectrometer, while NDVI was from ASD FieldSpec Pro spectrometer (referred to as NDVIASD) and GreenSeeker RT 100 (referred to as NDVIGS). The phenology detection method consists of two procedures: (i) smoothing the temporal CIred edge and NDVI data with the double logistic regression function to represent intra-annual vegetation dynamics, (ii) determining the phenological dates through extracting the maximum, minimum and zero-crossing points (FDmax, FDmin and FDzero) from the first derivative value of the smoothed NDVI and CIred edge temporal profiles. A comparison of remote sensing-based estimates with field observations over three growing seasons with different cultivars, planting densities and nitrogen (N) rates showed that CIred edge can accurately estimate the dates of jointing, middle booting and dough grain. NDVI from both spectrometers can be used to detect the dates of active tillering, middle heading and maturity. Specifically, NDVIGS yielded better performance than NDVIASD for estimating the three phenological dates. Compared with growing season and planting density, rice cultivar and N rate exhibited more significant impact on the accuracy for phenology detection. This work has great potential to provide valuable support for assessing crop growth status and providing precise management strategy. The dates of active tillering, jointing and maturity detected from a combination of CIred edge and NDVI could be useful for irrigation and fertilization management, and harvest determination, respectively.

A rapid method for calculating maximal and minimal inter-satellite distances

This paper proposes a method to rapidly and effectively calculate the maximal and minimal distances between a pair of satellites in which the leader is in an elliptic orbit. The principal idea of this method is simplifying the nonlinear squared distance function into a Taylor series with limited orders and further fitting the trigonometric functions in the derivative function of the simplified squared distance by piece-wise quadratic polynomials. By solving the zero-crossing points of the fitted quadratic curve, the critical points of the original nonlinear distance function are approximately determined. It turns out that the accuracy of the obtained solutions of the extreme distances depends on the number of intervals of the polynomial fitting. The bigger the number of intervals is, the better the accuracy. However, it is also noticed that the number of intervals is not necessary too big. For real applications a small value (e.g. 8) may be enough for the number of intervals. Besides, the method is apparently more effective for the small eccentricity cases. Finally, some simulations are further carried out to demonstrate the performances of this new method.

Laser differential fitting confocal microscopy with high imaging efficiency.

Based on the optical arrangement of a bipolar differential confocal microscopy (BDCM), laser differential fitting confocal microscopy (DFCM) is proposed in this paper using the feature of BDCM that a zero-crossing point (ZCP) of the axial response curve precisely corresponds to the focus of the system objective. A linear segment of the DFCM axial response around the ZCP is used to fit a straight line. Focus can be determined by solving the equations of the fitting lines, and then, the sample surface could be measured and reconstructed with a high resolution. Compared with the curve-fitting peak detection, which is an algorithm for focus detection widely used in conventional confocal microscopy, the line-fitting zero solution method used in DFCM has several advantages, such as high precision and sensitivity. Most importantly, precise focus detection can be realized using less data, i.e., DFCM has a high measurement efficiency. Furthermore, DFCM can effectively eliminate common-mode noise in a confocal microscopy system and has good noise suppression and disturbance resistance capability.

The effect of surface charge decay on the variation of partial discharge location

The accumulation of surface charges generated by a discharge at the solid-gas interface in a void is an important factor that can affect partial discharge (PD) characteristics. In this paper, with the help of the surface charge measurement system based on Pockels effect, the phenomenon of surface charge decay was observed by comparing its dynamic distribution during a PD sequence under variable voltage cycle. Moreover, the decay time of surface charge was measured. It is found that the decay rate of positive surface charge was much faster than that of negative one. The effect of surface charge decay on variation of partial discharge location was investigated when the voltage with variable cycle was applied. Two terms, the coincidence rate of hetero-discharge location (CRHEL) and the coincidence rate of homo-discharge location (CRHOL) were introduced to describe this effect. As the applied voltage cycle increased, CRHEL before and after voltage zero-crossing point decreased. Besides, CRHEL from a void between two dielectric surfaces (called VTD electrode) was larger than that from a void between a metal surface and a dielectric surface (called VMD electrode). Regarding VMD electrode, CRHEL for the case with negative discharges occurring in the former half-cycle was larger than that with positive discharges occurring in the former halfcycle. However, there was almost no difference about CRHEL for these two cases when VTD electrode was used. After the applied voltage cycle exceeded 500 ms, the coincidence phenomenon of homo-discharge location during negative half-cycle was observed in the usage of VMD electrode, and CRHOL became larger with voltage cycle increasing. As for VTD electrode, there was no coincidence of homo-discharge location. These results were attributed to the charge decay and the difference of discharge initiation position.

Advanced Design and Operation Consideration for Close-Connected Winding Permanent-Magnet Brushless DC Machine

Advanced design and operation consideration for the close-connected winding permanent-magnet brushless DC machine is proposed in this paper, including circulating current elimination, fault-tolerant control for the breakdown of a power electronic switch, and a sensorless control method. With the finite-element analysis, the influence of machine design parameters on circulating current is investigated. By properly controlling the status of power electronic switches, the coils being connected into the equivalent circuit can be changed to avoid the failure switch. Sensorless control is explored by detecting the zero-crossing point of electromotive force.

A Digital Hysteresis Current Controller for Three-Level Neural-Point-Clamped Inverter With Mixed-Levels and Prediction-Based Sampling

For a grid-tied three-level neural-point-clamped (NPC) inverter, fully digital hysteresis controller with simple variable hysteresis band is insufficient to stabilize switching frequency ( fs ). The challenge mainly comes from the restriction of analogue-to-digital converter (ADC) sampling frequency, which leads to inaccurate current-boundary-touching capture. As a result, $f_{s}$ jitter appears. This phenomena becomes much more serious around grid voltage zero-crossing points due to zero-approaching hysteresis band, where obvious $f_{s}$ variation happens. To stabilize $f_{s}$ in a fully digital manner, two techniques are proposed in this paper: the mixed-level scheme and the prediction-based sampling method. The former one is used to cope with the obvious $f_{s}$ variation around grid voltage zero-crossing points. It switches operating status from three-level state into two-level state around grid voltage zero-crossing points to enlarge the hysteresis band for digital implementation. The latter one is used to resolve $f_{s}$ jitter. It makes the sampling and switching to happen at the moment of current boundary-touching to achieve the most effective boundary-comparing with the lowest ADC sampling frequency. With these two techniques, $f_{s}$ of the grid-tied three-level NPC inverter could be well stabilized with a fully digital hysteresis controller, and therefore, high-quality grid-side could be achieved.

FIRST DERIVATIVE SPECTROSCOPIC METHOD FOR SIMULTANEOUS ESTIMATION OF MESALAZINE AND RIFAXIMIN IN SYNTHETIC MIXTURE

Objective: The present study was aimed to describe a simple, sensitive, rapid, accurate, precise and economical first derivative spectrophotometric method for the simultaneous determination of Mesalazine (MESA) and Rifaximin (RIFA) in synthetic mixture. Methods: The derivative spectrophotometric method was based on the determination of both the drugs at their respective zero crossing point (ZCP). The first order derivative spectra were obtained in 0.01 N NaOH and the determinations were made at 329.20 nm (ZCP of RIFA) for MESA and 292.80 nm (ZCP of MESA) for RIFA. The linearity was obtained in the concentration range of succinate 10-50 μg/ml for MESA and 10-50 μg/ml for RIFA. Results: The limit of determination was 0.321 μg/ml and 0.301 μg/ml for MESA and RIFA, respectively. The limit of quantification was 0.974 μg/ml and 0.912 μg/ml for MESA and RIFA, respectively. The mean recovery was 100.20 and 99.52% for MESA and RIFA, respectively. The method was found to be simple, sensitive, accurate and precise and was applicable for the simultaneous determination of MESA and RIFA in synthetic mixture. The results of analysis have been validated statistically and by recovery studies. Conclusions: The method was successfully applied to pharmaceutical synthetic mixture which is considered in approved patent which show no interference. The result of analysis has been validated statistically and by recovery studies. So, this method accurate, precise, robust, rugged and economic in nature.

Differential feature based hierarchical PCA fault detection method for dynamic fault

By sensor accuracy degradation or unwanted alternating current signals, sensor fault with zero cross point (ZCP) may occur in real systems and conventional data-driven fault detection methods could be invalid. In this regard, this paper proposes a hierarchical principal component analysis (PCA) fault detection method based on the differential features of dynamic faults to detect the fault with ZCPs. The main contribution of this work are as follows: (1) A new differential based feature extraction method is first proposed to well character the dynamic trend of the observation; (2) then, a hierarchical detection criterion is proposed according to the detection ability of each round of PCA anomaly detection; (3) it is convenient to extend the proposed method to other statistical based fault detection techniques whose detection criteria are also a distance defined by fault amplitude.

Characterization of MEMS Resonator Nonlinearities Using the Ringdown Response

We present a technique for estimation of the model parameters for a single-mode vibration of symmetric micromechanical resonators, including the coefficients of conservative and dissipative nonlinearities. The nonlinearities result in an amplitude-dependent frequency and a nonexponential decay, which are characterized from the ringdown response. An analysis of the amplitude of the ringdown response allows one to estimate the linear damping constant and the dissipative nonlinearity, and the zero-crossing points in the ringdown measurement can be used for characterization of the linear natural frequency and the Duffing and quintic nonlinearities of the vibrational mode, which arise from a combination of mechanical and electrostatic effects. [2015-0263]

Angular analysis of the B 0 → K *0 μ + μ − decay using 3 fb−1 of integrated luminosity

An angular analysis of the $B^{0}\rightarrow K^{*0}(\rightarrow K^{+}\pi^{-})\mu^{+}\mu^{-}$ decay is presented. The dataset corresponds to an integrated luminosity of $3.0\,{\mbox{fb}^{-1}}$ of $pp$ collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine $C\!P$-averaged observables and $C\!P$ asymmetries, taking account of possible contamination from decays with the $K^{+}\pi^{-}$ system in an S-wave configuration. The angular observables and their correlations are reported in bins of $q^2$, the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for $q^2$-dependent decay amplitudes in the region $1.1<q^{2}<6.0\mathrm{\,Ge\kern -0.1em V}^{2}/c^{4}$, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of $C\!P$-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions.

Position Sensorless Control Without Phase Shifter for High-Speed BLDC Motors With Low Inductance and Nonideal Back EMF

This paper presents a novel method for position sensorless control of high-speed brushless DC motors with low inductance and nonideal back electromotive force (EMF) in order to improve the reliability of the motor system of a magnetically suspended control moment gyro for space application. The commutation angle error of the traditional line-to-line voltage zero-crossing points detection method is analyzed. Based on the characteristics measurement of the nonideal back EMF, a two-stage commutation error compensation method is proposed to achieve the high-reliable and high-accurate commutation in the operating speed region of the proposed sensorless control process. The commutation angle error is compensated by the transformative line voltages, the hysteresis comparators, and the appropriate design of the low-pass filters in the low-speed and high-speed region, respectively. High-precision commutations are achieved especially in the high-speed region to decrease the motor loss in steady state. The simulated and experimental results show that the proposed method can achieve an effective compensation effect in the whole operating speed region.

Interleaved Current Control for Multiphase Converters with High Dynamics Mean Current Tracking

This paper presents a current control for high-power multiphase converters, where fast and precise current reference tracking is required, and limited switching frequency is present. The proposed control is based on a synchronization signal and current error comparison bands per phase. The control calculates the switching time that adjusts the phase current error zero-crossing points with the synchronization signal to control the current mean value and provide the correct phase shift among phases. The aforementioned comparison bands allow us to determine the current error slopes required to calculate the switching instants. This methodology permits the precise current reference tracking regardless the load voltage and the voltage drop in the semiconductor devices and in the series resistance of the phase inductors. Additionally, band-crossing information allows the fast detection of major changes in the current error, and the optimal system behavior decision, minimizing the transient time. Furthermore, the current control is stable in the complete duty cycle range, which is evaluated by means of a small-signal model. Experimental tests on a low-scale four-phase buck converter validate the proposal.

Online Adaptive Compensation Scheme for Dead-Time and Inverter Nonlinearity in PMSM Drive

Abstract: The paper focuses on a novel online dead-time compensation strategy for vector controlled permanent-magnet synchronous motor (PMSM). The proposed approach is composed of two parts. The first adaptive parameter-independent part is based on the monitoring of harmonic distortion in the d-axis current. Consequently, the criterion is defined as the sum of squared id current between two zero-crossing points of the phase currents. This criterion is minimized by PI controller and the output is slowly time-varying voltage, which is used to calculate the compensation voltages. This approach is extended by observer of persistent voltage disturbance that is based on the model of PMSM. The effectiveness of the proposed approach is verified through the simulations and experiments.

Cogging Torque Optimization of Novel Transverse Flux Permanent Magnet Generator With Double C-Hoop Stator

This paper deals with a sizing optimization approach to reducing the cogging torque and maximizing the flux linkage of a transverse flux permanent magnet generator with double C-hoop stator and flux-concentrated rotor. The previous investigations demonstrated that the cogging torque is significantly influenced by $k_{s}$ and $k_{r}$ , which denote the ratios of circumferential widths of stator hoop and rotor core to pole pitch, respectively. The 3-D finite-element method (FEM) is employed to investigate the relationship between the abovementioned ratios and the cogging torques of both single-phase and three-phase prototypes. The optimal ratios of $k_{s}$ and $k_{r}$ , which comply with the equation, i.e., $(k_{{ r}} >1-k_{{ s}} )\cap (k_{{ r}} >1-0.788~*~k_{{ s}} )=k_{r} >1-0.788~*~ k_{{ s}} $ , are selected, and the procedures are described. The FEM results show that the amplitude of the cogging torque can be reduced significantly due to the reshaped rotor core. Besides, two additional zero-crossing points can be observed with the increase in $k_{r}$ and the decrease in $k_{s}$ . The cogging torque can be decreased by 20% with a skewed rotor core. A three-phase prototype is optimally designed and manufactured to verify the optimization approach.