Output Signal Of Probe Research Articles

Single-Ended Eddy Current Micro-Displacement Sensor with High Precision Based on Temperature Compensation.

To measure the micro-displacement reliably with high precision, a single-ended eddy current sensor based on temperature compensation was studied in detail. At first, the principle of the eddy current sensor was introduced, and the manufacturing method of the probe was given. The overall design plan for the processing circuit was induced by analyzing the characteristics of the probe output signal. The variation in the probe output signal was converted to pulses with different widths, and then it was introduced to the digital phase discriminator along with a reference signal. The output from the digital phase discriminator was processed by a low-pass filter to obtain the DC component. At last, the signal was amplified and compensated to reduce the influence of temperature. The selection criteria of the frequency of the exciting signal and the design of the signal conditioning circuit were described in detail, as well as the design of the temperature-compensating circuit based on the digital potentiometer with an embedded temperature sensor. Finally, an experimental setup was constructed to test the sensor, and the results were given. The results show that nonlinearity exists in the single-ended eddy current sensor with a large range. When the range is 500 μm, the resolution can reach 46 nm, and the repeatability error is ±0.70% FR. Within the temperature range from +2 °C to +58 °C, the voltage fluctuation in the sensor is reduced to 44 mV after temperature compensation compared to the value of 586 mV before compensation. The proposed plan is verified to be feasible, and the measuring range, precision, and target material should be considered in real-world applications.

Precision measurement of 5-DOF rotational error motion using two multi-probe error separation methods

This study proposes a new method for the precision measurement of the 5-DOF error motion of rotating machines. The developed seven-probe error separation system uses two measurement units, consisting of an upper four-probe unit and a lower three-probe unit, for the separation of error signals. From the seven probe output signals, the profile signals of the measured surface and the 5-DOF error motion signals, including random components, can be precisely separated. An analysis was carried out to examine the effects of the intersection term by the 5-DOF error motion signals, which is an additional measurement error cause. Furthermore, an effective calculation process capable of calculating a precise surface profile and error motion signal by compensating for the effect was proposed. Numerical validation tests and measurement experiments were performed. This showed it was possible to make accurate measurements by separating the 5-DOF error motions and surface profile signals and using a compensation calculation process. In addition, the effect of the stability error of the probe, which can be a significant factor in increasing measurement uncertainty, on the measurement results was observed and analyzed. Based on the geometric relationship of the measurement system, a process for estimating the expected effect of the stability error of the probe on the measurement result was presented. By applying this process, it is possible to determine the scale of probe stability error to secure the measurement reliability required when selecting a probe used in the system.

Non-Steady State NMR Effect and Application on Time-Varying Magnetic Field Measurement.

The measurement of a time-varying magnetic field is different from a constant magnetic field, due to its field intensity variation with time. Usually, the time-varying magnetic field measurement converts the solution of the magnetic induction intensity into the calculation of the induced electromotive force (EMF); then, the magnetic induction intensity is obtained by the time integration of the EMF, but the process is vulnerable to external interference. In this paper, a non-steady state nuclear magnetic resonance (NSS-NMR) scheme for the measurement of a time-varying magnetic field is proposed. In a time-varying magnetic field environment, an RF excitation signal with a certain frequency bandwidth is applied to excite the nuclear spin system. The NSS-NMR signal, which varies with time in the frequency range corresponding to the frequency bandwidth of the RF excitation, could finally be obtained after a series of processing of the probe output signal. During the NSS-NMR experiment, an orthogonal dual-coil probe is adopted to synchronously generate the RF excitation and induce the probe output signal. Moreover, a directional coupler that utilized in the experiment outputs a reference signal from the coupling port for the subsequent signal processing. The experimental results show that the weak NSS-NMR signal is indeed observed. The longitudinal time-varying magnetic field ranges from 0.576 T to 0.582 T, which is inverted by the Larmor precession relationship, have been successfully detected based on the so-called NSS-NMR effect.

An Efficient Method for Predicting the Output Signal of an Eddy Current Probe Around the Edge of a Conductive Cylindrical Rod

We propose a semi-analytical model to predict the output signal of an eddy current probe around the edge of a conductive cylindrical rod. The proposed model is based on the truncated region eigenfunction expansion method and uses the second-order vector potential to formulate the resultant boundary problem. The use of appropriate boundary conditions on the truncation locations leads to less complex eigenvalue equations which remarkably increases the computation speed. The validity and computation efficiency of the proposed model are demonstrated by comparing the simulation results of several case studies with measurements and those obtained using a commercial finite element code.

Simultaneous Measurement of Radius and Coating Thickness of Finite Length Metal Rods by Eddy Current Surface Probes

The paper proposes an efficient inverse method for simultaneous measurement of radius and coating thickness of a finite length metal rod, using the output signal of a surface eddy current probe. The proposed method adopts a physical model for iterative solution of the inverse problem. It utilizes a hybrid conjugate gradient optimization algorithm in the inversion process, and adopts an efficient forward problem solver to obtain the predicted probe output signal in each iteration. The solution of the forward problem is based on the truncated region eigenfunction expansion method and uses the even/odd parity solution decomposition to treat the governing boundary value problem. The main feature of the proposed inversion method is its robustness in the presence of noise regardless of the choice of the initial values. Experimental and simulation results are provided to demonstrate the validity of the proposed methods for solving the forward and inverse problems. It has been shown that the rod radius and coating thickness can be measured with an error less than 5% of the true value when the probe is located at the half distance from the edge of the rod.

Measurement and Suppression of Transverse Optical Pumping in a Spin-Exchange Relaxation-Free Co-Magnetometer

The transverse optical pumping (TOP) introduced by a probe beam can result in a polarization error in the output signal of a spin-exchange relaxation-free (SERF) co-magnetometer. In this paper, a model capable of quantitatively evaluating TOP in a SERF co-magnetometer is established based on three characteristics of the probe beam. According to this model, a novel fast measurement method for TOP based on steady-state response output signals and longitudinal polarization information is proposed. Furthermore, a method of suppressing TOP based on counter-propagating beam is suggested, and the circular polarization-induced TOP is effectively reduced by finely adjusting the amount of phase retardation of an octantal waveplate. Eventually, the counter-propagating beam scheme achieves a 22.74% TOP suppression ratio. The stability of both the short- and long-term outputs of the SERF co-magnetometer is improved and the lowest point of the Allan variance is 0.006°/h better than the original. Moreover, the coupling effect between the probe beam power fluctuation and output signal bias of the SERF co-magnetometer is decreased.

ADMISSIBILITY DIAGNOSTICS OF USING A FOERSTER PROBE AS PART OF A MAGNETOMETER

We have discussed a diagnostics method to assess the admissibility of using a Foerster probe as part of a magnetometer. The diagnostics is based on the compatibility analysis of the magnetic field (MF) induction (B) conversion by a Foerster probe with the parameters of a specific series of Foerster probe output signal converters (OSC). As a reference source of MF, we have used the Earth’s MF. The analysis uses a Foerster probe magnetometer designed according to the MF compensation method in the Foerster probe core piece. The subject of our analysis is the value of the OSC output signal under normal climatic conditions (NCCs), when the Foerster probe is exposed to extreme temperatures. Following the diagnostics, we have made a YES/NO decision on the admissibility of using a Foerster probe with OSCs of this series. As OSC parameters, that limit the use of a Foerster probe, we have adopted the values of the minimum and maximum codes of a digital-to-analog OSC converter, as allowed by relevant documents. The first two diagnostics stages are carried out with inductions of ±Bcon under NCCs, taking into account the Foerster probe zero offset. In this case, Bcon ˂ Вmax, where Вmax is the Foerster probe’s working range. Two subsequent diagnostics stages are carried out using the calculated and experimental characteristics, taking into account the Foerster probe zero offset under effect of extreme temperatures of different signs. We have demonstrated the temperature error specifics and presented the diagnostics algorithm.

Reconstruction of surface radial profiles of the electrophysical characteristics of cylindrical objects during eddy current measurements with a priori data. The selection formation for the surrogate model construction

The prospects of solving the multi-parameter inverse problem of eddy current measurements are shown. This problem is the identification of the radial profiles of the electrophysical characteristics of cylindrical control objects by the approximation method. The method involves the use of a priori information about the testing objects obtained as a result of mathematical modelling. The problem statement is completed, the main stages of its effective solution are determined. A universal mathematical model of the measurement process is presented, a set of programs for its implementation in the Python 3 is created. The adequacy of the created software is proved by calculations on the test models for simple cases when analytical solutions are known. A series of numerical experiments using a set of programs are carried out. The experiments have shown the possibility of distinction of distribution profile types of material characteristics of modelling objects. The preparatory stage of constructing an approximation surrogate model for the case of the dependence of the output signal of the eddy current probe on the electrical conductivity and magnetic permeability at a fixed excitation frequency has been completed. The preparatory stage includes the Design of Computer Experiment creation based on Sobol’s LPt-sequences and the formation of training sample based on an “accurate” electrodynamic model. The ways of generalization to more complex cases of solving measurement problems are indicated.

Conductivity inversion of unidirectional CFRP laminate based on ECT using neural network

For the electrical anisotropy of carbon fiber reinforced polymer (CFRP), conductivity of unidirectional CFRP laminate in three directions was inverted in this paper. The three-dimensional eddy current electromagnetic model of unidirectional composites was constructed by ANSYS software, and the influence of the electrical conductivity of the material on the detection signal of the probe in the longitudinal, transverse and thickness directions was studied. In order to improve the amplitude of the probe output signal induced by the change of conductivity, the optimal detection angle of the eddy current probe was determined. On this basis, the relationship between the conductivity and the detection signal was studied to estimate the initial values of the conductivity based on the experimental data obtained by the eddy current testing (ECT). According to the forward model, the theoretical probe voltage under the estimated conductivity were calculated. The database consisting of conductivity and corresponding theoretical results was built for the neural network to construct the mapping that can estimate conductivity by experimental results. Using neural network for iteration, the conductivity was inverted quickly and precisely.

Measurement and Evaluation of Shaft Torsional Vibrations Using Shaft Instantaneous Angular Velocity

Online evaluation of possible failures of a turbine is a key factor for a successful long-term turbine operation. Fluctuations of generator air-gap torque, caused for example by nonstationary conditions of electrical power grid, influence shaft torsional vibrations as well as rotating blades vibrations. Symptoms of shaft torsional vibrations are not measurable by normally used relative shaft vibrations sensors, so special measurement must be used. The direct consequence of shaft torsional vibrations is local acceleration or deceleration of shaft circumference when it is measured by a stationary sensor. This paper deals with a measurement method using an optical probe measuring the passage of black and white stripes of a zebra tape, which is stuck on the rotor. The shaft torsional vibrations manifest themselves as a phase modulation of the optical probe output signal, so the sampling rate influence the achievable resolution of the calculated shaft vibrations. The presented method for the calculation of the shaft torsional vibrations is based on the evaluation of shaft instantaneous angular velocity. The advantage of this method is a direct compensation of possible nonregular geometry of the zebra tape. The analysis of shaft torsional vibrations evaluation using this method is supplemented by two case studies from the authors' current work.

Determination of 3-D velocity field from the four hot-wire output signals using „three against one“ algorithm

The advantage of ?three against one? algorithm for determination of 3-D velocity field from the four hot-wires output signals is presented. Three tests of this algorithm, with differently defined dependence between velocity components and probe output signals are conducted. Test with generalized hot-wire cooling law shows better results in comparison to the test based on King-Jorgensen equations. It is shown that ?three against one? algorithm has some advantage near the border of uniqueness range in comparison to the existing algorithms.

Progress and Trends in AIE-Based Bioprobes: A Brief Overview.

Luminescent bioprobes are powerful analytical means for biosensing and optical imaging. Luminogens featured with aggregation-induced emission (AIE) attributes have emerged as ideal building blocks for high-performance bioprobes. Bioprobes constructed with AIE luminogens have been identified to be a novel class of FL light-up probing tools. In contrast to conventional bioprobes based on the luminophores with aggregation-caused quenching (ACQ) effect, the AIE-based bioprobes enjoy diverse superiorities, such as lower background, higher signal-to-noise ratio and sensitivity, better accuracy, and more outstanding resistance to photobleaching. AIE-based bioprobes have been tailored for a vast variety of purposes ranging from biospecies sensing to bioimaging to theranostics (i.e., image-guided therapies). In this review, recent five years' advances in AIE-based bioprobes are briefly overviewed in a perspective distinct from other reviews, focusing on the most appealing trends and progresses in this flourishing research field. There are altogether 11 trends outlined, which have been classified into four aspects: the probe composition and form (bioconjugtes, nanoprobes), the output signal of probe (far-red/near-infrared luminescence, two/three-photon excited fluorescence, phosphorescence), the modality and functionality of probing system (dual-modality, dual/multifunctionality), the probing object and application outlet (specific organelles, cancer cells, bacteria, real samples). Typical examples of each trend are presented and specifically demonstrated. Some important prospects and challenges are pointed out as well in the hope of intriguing more interests from researchers working in diverse areas into this exciting research field.

ANALYSIS OF SURFACE DEFECTS OF ALUMINUM AND ITS ALLOYS WITH A SCANNING KELVIN PROBE

Currently, the use of probe electrometry in non-destructive testing is constrained by the complexity of measurement results interpretation. An output signal of electrometric probe depends on a number of physical and chemical parameters of surface including chemical composition variations, stresses, dislocations, crystallographic orientation of a surface, etc. The study aims to the use of probe electrometry methods for nondestructive testing and analysis of precision metal surfaces’ defects after different treatment or processing. Control of surface defects of aluminum and its alloys was performed with a scanning Kelvin probe technique. The results of scanning were plotted in a form of contact potential difference (CPD) distribution map. Additionally, a histogram of CPD values distribution and statistical characteristics including the expectation of CPD mean value and histogram half-width were calculated either for the whole distribution or for each individual mode in a case of multimodal distribution. The spatial CPD distribution of A99 aluminum and AMG-2 alloy surfaces after electrochemical polishing and diamond finishing was studied. An additional study was held for AMG-2 surface after the formation of 30 microns thick specific nanostructured alumina oxide surface layer. Higher quality surfaces have characterized as more homogeneous distribution of the physical properties (at half-width distribution histogram). Surfaces with higher mechanical strength and overall better mechanical properties found to have lower CPD values that correspond to higher electron work function and surface energy. The presence of the second mode in the CPD distribution histogram indicates the significant proportion of defect areas on the sample surface. Analysis of visualized CPD distribution maps using defined criteria allows detecting and characterizing such defects as residual stress areas, areas with reduced microhardness, surface contamination spots, corrosion defects. This provides the possibility of rapid nondestructive testing and diagnostic of precision metal surfaces, in particular the starting substrates for sensitive elements and sensory devices manufacture.

Heat Transfer Analysis and Modification of Thermal Probe for Gas-Solid Measurement

The presented work aims to measure the gas-solid two-phase mass flow-rate in pneumatic conveyor, and a novel modified thermal probe is applied. A new analysis of the local heat transfer coefficients of thermal probe is presented, while traditional investigations focus on global coefficients. Thermal simulations are performed in Fluent 6.2 and temperature distributions of the probe are presented. The results indicate that the probe has obviously stable and unstable heat transfer areas. Based on understanding of probe characteristics, a modified probe structure is designed, which makes the probe output signal more stable and widens the measuring range. The experiments are carried out in a special designed laboratory scale pneumatic conveyor, and the modified probe shows an unambiguous improvement of the performance compared with the traditional one.

An Efficient Modeling Technique for Analysis of AC Field Measurement Probe Output Signals to Improve Crack Detection and Sizing in Cylindrical Metallic Structures

The paper proposes an efficient modeling technique for predicting the output signal of an AC field measurement (ACFM) probe when encountering a fatigue crack in a cylindrical metallic structure. The proposed technique is used to determine the electromagnetic fields around an arbitrary-shape surface crack in a cylindrical metal, induced by a high frequency alternating-current-carrying coil of arbitrary shape. The modeling technique involves two steps. First, the finite-difference method is used to solve the governing Laplace equation inside the crack region. Then, the normal component of magnetic field at the crack opening on the metal is obtained to derive a closed-form solution in the Fourier domain for the regions outside the crack. Experimental and theoretical results associated with prototype ACFM probes confirm the validity of the proposed technique while demonstrating its remarkable computation efficiency. The latter is an important feature of the proposed modeling technique as a fast “forward” solver that results in a remarkable improvement in solving the “inverse” problem required for the sizing of fatigue cracks in cylindrical metallic structures, particularly in real-time applications.

Real-Time Dynamic Spectrum Analysis for Plasma Electron Density and Faraday Rotation Angle Measurement on HL-2A**supported by National Natural Science Foundation of China (Nos. 11375195 and 11275059) and the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB104003, 2014GB109001)

Electron density and Faraday rotation angle are important physical parameters in nuclear fusion research. To measure them simultaneously, the three-wave polarimeter/interferometer diagnostic system is applied. Both the final probe output signal and the reference signal contain three frequency components. The time-varying phase difference curve of each frequency component can be measured by the Real-time Dynamic Spectrum Analysis (RDSA) method based on Field-Programmable Gate Array (FPGA). The phase difference precision is better than 0.1° and the real-time feedback delay is less than 1 ms, which satisfy the requirements of HL-2A.

Fast circuit model for interaction of open‐ended rectangular waveguide probes with arbitrary‐shape surface cracks in metals

The study proposes a fast modelling technique to predict output signal of an open-ended rectangular waveguide when scanning an arbitrary-shape surface crack in a metal. In this technique, the crack is first segmented into an appropriate number of short rectangular waveguides each of which is modelled by a two-port network with an equivalent RLC circuit. The generalised scattering matrix technique is then used to predict the probe output signal. The efficiency of the proposed model is demonstrated by comparing the simulation results of several case studies with measurements and those obtained using the mode-matching method and a commercial finite integration technique code.

Real-Time Processing of Multifrequency Eddy Currents Testing Signals: Design, Implementation, and Evaluation

The design, implementation, and evaluation of a real-time digital signal processing architecture to generate and process multifrequency signals for eddy currents testing is described in this paper. This architecture is implemented on a dedicated instrument whose processing core is a field-programmable gate array. Stimulus generation is achieved using direct digital synthesis with some important improvements to reduce spurious frequency components. An in-phase and in-quadrature demodulation scheme is implemented to estimate the real and imaginary parts of the probe output signal. A cascaded integrator comb decimator is used to lower the sampling frequency and then allow narrowband filtering with low resources. The proposed architecture is able to generate and process the stimulus and input data at 125 MSamples/s and to estimate the input data components at 1.25 MSamples/s rate for eddy-currents with multiple simultaneous testing frequencies between 2.5 kHz and 10 MHz. Experimental validation is performed using a set of synthetic defects and two stimulus with different spectral composition.

Active vibrations control of journal bearings with the use of piezoactuators

Rotor instability is one of the most serious problems of high-speed rotors supported by sliding bearings. With constantly increasing parameters, new machines problems with rotor instability are encountered more and more often. Even though there are many solutions based on passive improvement of the bearing geometry to enlarge the operational speed range of the journal bearing, the paper deals with a working prototype of a system for the active vibration control of journal bearings with the use of piezoactuators. The controllable journal bearing is a part of a test rig, which consists of a rotor driven by an inductive motor up to 23,000rpm. The actively controlled journal bearing consists of a movable bushing, which is actuated by two piezoactuators. The journal vibration is measured by a pair of proximity probes. The control system enables run-up, coast-down and steady-state rotation. A real-time simulator dSpace encloses the control loop. Force produced by piezoactuators and acting at the bushing is controlled according to error signals derived from the proximity probe output signals. As it was proved by experiments the active vibration control extends considerably the range of the operational speed.

Real-Time mRNA Measurement during an in Vitro Transcription and Translation Reaction Using Binary Probes

In vitro transcription and translation reactions have become popular for a bottom-up approach to synthetic biology. Concentrations of the mRNA intermediate are rarely determined, although knowledge of synthesis and degradation rates could facilitate rational engineering of in vitro systems. We designed binary probes to measure mRNA dynamics during cell-free protein synthesis by fluorescence resonance energy transfer. We tested different mRNA variants and show that the location and sequence environment of the probe target sites are important parameters for probe association kinetics and output signal. Best suited for sensitive real-time quantitation of mRNA was a target site located in the 3' untranslated region, which we designed to reduce secondary structure. We used this probe-target pair to refine our knowledge of mRNA dynamics in the commercially available PURE cell-free protein synthesis system and characterized the effect of TetR repressor on mRNA synthesis rates from a T7 promoter.