Inductive Measurement Technique Research Articles

A Self-Sensing Method for Electromagnetic Actuators with Hysteresis Compensation

Self-sensing techniques are a commonly used approach for electromagnetic actuators since they allow the removal of position sensors. Thus, costs, space requirements, and system complexity of actuation systems can be reduced. A widely used parameter for self-sensing is the position-dependent incremental inductance. Nevertheless, this parameter is strongly affected by electromagnetic hysteresis, which reduces the performance of self-sensing. This work focuses on the design of a hysteresis-compensated self-sensing algorithm with low computational effort. In particular, the Integrator-Based Direct Inductance Measurement (IDIM) technique is used for the resource-efficient estimation of the incremental inductance. Since the incremental inductance exhibits a hysteresis with butterfly characteristics, it first needs to be transformed into a B-H curve-like hysteresis. Then, a modified Prandtl–Ishlinskii (MPI) approach is used for modeling this hysteretic behavior. By using a lumped magnetic circuit model, the hysteresis of the iron core can be separated from the air gap, thus allowing a hysteresis-compensated estimation of the position. Experimental studies performed on an industrial switching actuator show a significant decrease in the estimation error when the hysteresis model is considered. The chosen MPI model has a low model order and therefore allows a computationally lightweight implementation. Therefore, it is proven that the presented approach increases the accuracy of self-sensing on electromagnetic actuators with remarkable hysteresis while offering low computational effort which is an important aspect for the implementation of the technique in cost-critical applications.

Qualitative and Quantitative Analysis of Different Inductance Measurement Techniques for IPM Synchronous Machines

The accurate estimation of equivalent circuit parameters (EEC) is necessary for performance analysis and control of electric drives using the analytical models of electrical machines. The analytical models of PM motor assume constant values of d and q axis inductances. Since the B vs. H curve of the lamination material is non-linear, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L_{d}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L_{q}$</tex-math></inline-formula> inductances vary as the stator current increases. So, the assumption of constant inductances results in an erroneous prediction of the motor’s behavior. Hence, an accurate estimation of nonlinear variation of inductances in PM motors is necessary. There are many techniques specified in standards and literature for the evaluation of IPM machine inductances. However, a reliable method to capture the nonlinear variation of inductances is not discussed. This work gives a comparative analysis of various inductance measurement techniques for the interior permanent magnet (IPM) machines to capture the nonlinear variation of inductances with current based on motor performance. Statistical and qualitative analysis of experimental and FEA results on an IPM motor design is done in this work to determine a reliable inductance measurement technique.

Analysis of Current Ripples in Electromagnetic Actuators with Application to Inductance Estimation Techniques for Sensorless Monitoring

Techniques for estimating the plunger position have successfully proven to support operation and monitoring of electromagnetic actuators without the necessity of additional sensors. Sophisticated techniques in this field make use of an oversampled measurement of the rippled driving current in order to reconstruct the position. However, oversampling algorithms place high demands on AD converters and require significant computational effort which are not desirable in low-cost actuation systems. Moreover, such low-cost actuators are affected by eddy currents and parasitic capacitances, which influence the current ripple significantly. Therefore, in this work, those current ripples are modeled and analyzed extensively taking into account those effects. The Integrator-Based Direct Inductance Measurement (IDIM) technique, used for processing the current ripples, is presented and compared experimentally to an oversampling technique in terms of noise robustness and implementation effort. A practical use case scenario in terms of a sensorless end-position detection for a switching solenoid is discussed and evaluated. The obtained results prove that the IDIM technique outperforms oversampling algorithms under certain conditions in terms of noise robustness, thereby requiring less sampling and calculation effort. The IDIM technique is shown to provide a robust position estimation in low-cost applications as in the presented example involving a end-position detection.

High-resolution inductive measurement of electrical resistivity and density of electromagnetically levitated liquid metal droplets.

A new device for the inductive measurement of electrical resistivity and density of liquid metals and semiconductors is presented. It is integrated in two electromagnetic levitation facilities operating under microgravity. As a result, the completely noninvasive handling and measuring of the metallic melt enables the extension of the accessible sample temperature range far into the undercooled liquid state below the melting point. The microgravity environment permits the undisturbed joining of the containerless inductive sample handling method by the electromagnetic levitation with the inductive sample measurement technique. The following sections explain in detail the basic principles and the technical realization of the whole measurement apparatus and present experimental data showing its high resolution resulting from the combination of microgravity, electromagnetic levitation, and inductive measurement technique.

Spectral Domain Optical Coherence Tomography for Non-Destructive Testing of Protection Coatings on Metal Substrates

In this paper we demonstrate that optical coherence tomography (OCT) is a powerful tool for the non-destructive investigation of transparent coatings on metal substrates. We show that OCT provides additional information which the common practice electrical impedance spectroscopy (EIS) cannot supply. First, coating layer thicknesses were measured and compared with reference measurements using a magnetic inductive (MI) measurement technique. After this validation of the OCT measurements, a customized sectioned sample was created to test the possibility to measure coating thicknesses with underlying corrosion, which cannot be analyzed accurately by MI or EIS measurements. Finally, we demonstrate the benefit of OCT on a standard sample. The OCT measurements provide the correct coating layer thickness with high lateral resolution and even enable metal and corrosion layers to be distinguished from each other.

Simple method for measuring the equivalent series inductance and resistance of electrolytic capacitors

A simple equivalent series inductance (ESL) and equivalent series resistance (ESR) measurement technique for capacitors is presented. A low-cost square waveform voltage source coupled with a reference resistor can be used to measure the ESL, ESR and capacitance of an electrolytic capacitor. By connecting a capacitor in series with a reference resistor, the equivalent output step response of the capacitor voltage reveals the ESL and ESR of the capacitor. To effectively capture the output step response, a square input waveform is used instead. The square waveform voltage source can easily be realised using a DC voltage source and simple switching devices. Experimental results are included to demonstrate the effectiveness of the proposed scheme.

Line inductance measurement by using commutation time in line commutated converters

Finding line inductance using wiring diagrams of the network is usually difficult or even impossible. In general, line inductance has to be measured in a simple nondisruptive way without service interruption. Several line inductance measurement techniques have been suggested previously, but they suffer from a number of limitations. In this paper, a novel line inductance measurement technique that uses the current commutation in a line-commutated converter is proposed. An expression for the line inductance as a function of phase-to-phase voltage, utility angle frequency, load current, triggering angle α and commutation time is procured. The line inductance is calculated by recording the commutating current waveforms by means of an accurate oscilloscope and measuring the other required values. Because of its simplicity, diode converter is employed in the experimental circuit when α = 0. The experiment is repeated for the case in which the phase inductances are different, and these phase inductances are calculated. To verify the performance of the proposed line inductance measurement technique, the known inductances are added in series to the line phase inductances. The results obtained show that the line inductance can be measured by the proposed measurement method precisely below 6% error. Finally, the error sources that may be encountered when the proposed method is applied are discussed.

Electrical resistivity measurement of liquid metals

Two facilities for the complete noninvasive measurement of the electrical resistivity of liquid metals above the melting temperature and in the undercooled liquid state below the melting temperature are presented: a ground-based facility that was built up in our laboratory and the microgravity facility TEMPUS. Both facilities are unique in combining the containerless positioning method of electromagnetic levitation with the contactless, inductive resistivity measurement technique, thereby enabling for the first time measurements in the undercooled liquid state of a metal. The principles and technical realizations of the levitation and measurement technique of both facilities are presented. Furthermore, experimental resistivity data for Cu60Ni40 as well as Co80Pd20 alloy are presented which indicate atomic ordering effects in the undercooled melt.

Effect of porosity and metallic insertions on electrical resistivity of A2011 aluminium alloy

A rotational, contactless inductive measurement technique has been used to determine the effect of pores and metallic insertions on the electrical resistivity of A2011 aluminium alloy at different temperatures. It is shown that the electrical resistivity increases with the total volume of pores, and is also dependent on the location and orientation of pores. Additional energy losses were found on the contact surfaces between sample and insertions.

An integrated on-line oil analysis method for condition monitoring

An on-line oil monitoring system offers a suitable solution to the practical problemsencountered in monitoring the conditions of machinery equipment. The objective ofthis paper is to present a systematic method for analysing wear particles in thelubricant used in a diesel engine, in a laboratory setting. An integrated on-line oilmonitoring system, which combines an inductive transducer with a fibre optictransducer, was developed to primitive design stage and some experiments havebeen done. The inductance transducer, whose operation is based on an inductivemeasurement technique, can detect large ferrous and non-ferrous wear debris. Aparticle’s material properties reflect its origin, and the frequency can be usedfor estimating wear particle size. The fibre optic transducer can detect smallparticles and is used for inspection of oil contamination levels. The integrated systemcombines the virtues of two measurement methods, extends the detection range andmeaningfully improves the reliability of oil monitoring. So it has great promise and thereare prospects for application as soon as the solutions to certain problems arefound.

Electrical resistivity measurements on binary Al-15 wt-%In alloy

A rotational contactless inductive measurement technique has been used to determine the electrical resistivity of an Al-15In (wt-%) binary alloy over a wide range of temperatures. It is shown that the electrical resistivity depends on the distribution of the indium within the aluminium matrix. The results can be considered as a first attempt to detect the onset of the sedimentation process, which occurs in alloys of this type, by measuring the electrical conductivity of immiscible alloys.

Electrical Resistivity of Undercooled Liquid Cu-Ni Alloys

Measured values for the electrical resistivity of undercooled liquid Cu-Ni alloys of different compositions are presented. The experiments were performed in a facility that combines the containerless positioning method of electromagnetic levitation with the contactless inductive resistivity measurement technique. For high nickel concentrations, i.e., for the liquid Cu20Ni80 and Cu40Ni60 alloys, the electrical resistivity shows, as well as for pure nickel and pure copper, the typical linear temperature dependence in the whole range from above to below the liquidus temperature. A significant deviation from the linear behavior occurs for liquid Cu60Ni40 and, less distinct, also for liquid Cu80Ni20. This is explained by a formation of nickel associates in the melt that influence the scattering cross section of the conduction electrons.

Electrical and thermal conductivity of A319 and A356 aluminum alloys

A rotational contactless inductive measurement technique has been used to measure the electrical resistivity of A319 and A356 aluminum alloys at both solid and liquid states. The method is based on the phenomena that when a conducting material rotates in a magnetic field, circulating eddy currents are induced and generate an opposing torque, which is proportional to the electrical conductivity of the material. The technique was checked and calibrated with pure aluminum where considerable electrical resistivity data exist in the literature. Wiedemann-Franz-Lorenz law was used to estimate the thermal conductivity of A319 and A356 aluminum alloys in liquid state.

Electrical conductivity measurements in liquid metals by rotational technique

The rotational contactless inductive measurement technique has been developed to measure the electrical conductivity of liquid metals. This method is based on the phenomena when a conductor material rotates in a magnetic field, circulating eddy currents are induced and generate a damping torque proportional to the electrical resistivity of the material. The technique was tested to measure the conductivity of five conductors and one low melting composite (LMA-158).

Inductance measurements in thin films

We present a new inductance measurement technique using a multi-frequency LCR meter. The inductance of superconducting (YBCO) delay lines was measured both as a function of temperature and bias current. The measured temperature dependence of the change in inductance for both meander and straight lines shows a square dependence on temperature, in good agreement with an unconventional pairing state. The effective magnetic penetration depth can be determined from the theoretical expression of the inductance for the case of a microstrip configuration with two identical superconducting films. The current-controlled inductance is well described by a modified Ginzburg - Landau equation.

Package inductance characterization at high frequencies

This paper describes a package inductance measurement technique based on network analysis and lumped element package model. Advantages of this technique include: 1. Measuring inductance over the same high operating frequencies of today's high-speed CMOS and ECL chips. 2. Providing information on a package's resonance frequencies and determining the limit of the lumped element model and 3. Utilizing a simple one-port measurement method, procedure and fixture design. Different packages and interconnects including a 120QFP, a 296TAB tape, a multilayer 224PGA and bonding wires of different length were characterized using this technique. Where possible, the inductance results obtained by this technique were compared with both modeling data and measurement data obtained by the conventional LCZ technique. In addition, the experiments were extended to compare the effective inductance of the ground path of one-metal and two-metal 360TAB tapes. The results provide important guidelines in determining design tradeoffs between one-metal and two-metal TAB tapes. >

Rheomagnetic properties of mixed magnetic particle suspensions

Single-domain magnetic particles are the essential ingredient of magnetic tapes, particulate recording disks and magnetic stripes. The particles are single-domain γ-Fe 2O 3, CrO 2 or barium ferrite, and non-magnetic α-Fe 2O 3 mixture. Each of these particles has intrinsic coercivity, which should be matched with the magnetic field strength of the writing element of a particular device. In this study a magnetic inductance measurement with low field strength was employed to obtain the magnetic permeability of suspensions containing two of the particle types mixed together as a function of composition and volume fraction of particles. The bulk magnetic property B is a linear combination of the contributions from each particle type such that the “excess” inductance is L − L s = Σφ iB i where φ i is the volume fraction and B i , is the magnetic property of particle type i. For the non-magnetic α-Fe 2O 3, B i = 0. This allows the formulation of mixed particle suspensions to obtain a desired property for custom-designed magnetic particle coatings. However, mixing magnetic particle types will broaden or produce a bimodal switching field distribution. This may affect the squareness of the magnetic hysteresis loop. These properties should be taken into account for the design of a practical magnetic coating with mixed particle suspension. Another requirement of the magnetic particle suspensions is that they remain well dispersed, even though strong magnetic forces between the particles promote flocculation. An extension of the inductance measurement technique is employed to study the flocculation of a suspension containing magnetic γ-Fe 2O 3 and non-magnetic α-Fe 2O 3. The presence of the α-Fe 2O 3 decreases the flocculation state of the suspension. Thus the suspension stability is enhanced by incorporating a small amount of non-magnetic particles in addition to surfactant.

Interpretation of the harmonic response of superconducting films to inhomogeneous ac magnetic fields.

We present a quantitative analysis of the response of a thin superconducting film to an applied nonuniform ac magnetic field. The analysis is directly applicable to the single-coil inductive measurement technique where a small coil driven by an ac current produces a nonuniform field, with ${\mathit{J}}_{\mathit{C}}$ determined by the appearance of a third-harmonic component of the voltage generated across the coil. We derive a simple model to explain the response of the film to the applied magnetic field in the absence of weak links. This model is used to predict the third-harmonic voltage generated across the coil. The derivation of the model explains why superconducting films having thicknesses even less than the penetration depth screen out the nonuniform ac magnetic fields generated by the coil. A simplified version of the model yields analytic expressions that describe the magnitude and phase of the third-harmonic component at high drive currents while the full model yields excellent agreement with experimental measurements for our highest quality epitaxial films. In other films, the presence of weak links leads to a characteristic signature in the harmonic response at low drive currents. We have also found that ion irradiation can reduce the critical current densities by significant amounts without introducing weak links into the film.

Percolative reconciliation between resistive and magnetic measurements of the transition temperature in HTS thin films

Several Bi-Sr-Ca-Cu-O thin films have been produced ex situ by sequential thermal evaporation. Characterizing the transition temperatures Tc of these films, a constant discrepancy between resistive and inductive measurements is observed. The resistive van der Pauw technique indicates Tc (onset) typically above 90 K and Tc (zero) at around 78 K. However, the Tc (onset) for these same films is not seen by an inductive measurement, in which the film surface is in physical contact with a flat spiral coil, inducing changes in the coil inductance during the superconductivity transition. Conversely, the inductive transition starts around 5 K above the resistively obtained Tc (zero). Percolation theory is employed in an attempt to explain this discrepancy and to establish generally how Tc (zero) can be found from the resulting curve in the inductive measurement technique.

Investigation of inter- and intragrain critical currents in high Tc ceramic superconductors

Polycrystalline sintered bulk samples of REBa2Cu3O7 with RE = Y, Gd were studied by a.c. susceptibility and an inductive measurement technique which allows the separation of intergrain (transport) from intragrain critical current density. Field and temperature dependence of the intergrain current are compared with theoretical predictions for a weakly coupled grain structure. Up to fields 0.3 T the weak link character of the intergrain current predominates. At higher fields it changes and points to a percolation current via superconducting grain boundaries. A quantitative correlation between intragrain current and twin spacing is hidden, probably by oxygen deficiency in the grain interior. No variation of the intragrain critical current density with temperature is observed up to 85 K in a textured specimen.