We describe D-permeameter originally designed by Trnka and later improved by Fajt and Kaspar and we analyze its precision for the measurement of different soft magnetic materials. The device measures DC hysteresis loops using compensation method, so that H and B can be calculated from the magnetization and compensation currents. The differences from results obtained by other standard methods are below 2%.
Stejně jako původní vydání knihy Elektrická měření – přístroje a metody z roku 2003 i toto shrnuje informace týkající se oblasti elektrických a magnetických měření na úrovni absolventa inženýrského studia elektrotechnických oborů. Vzhledem k prudkému rozvoji elektroniky a číslicové techniky však byla náplň většiny kapitol značně modernizována popř. rozšířena a část věnovaná analogovým přístrojům naopak významně zredukována. V publikaci jsou vysvětleny základní principy používané v současné době pro měření elektrických popř. magnetických veličin a principy nejčastěji používaných metod pro měření ostatních fyzikálních veličin s mezipřevodem na elektrický signál. Jsou popsány též běžně používané měřicí přístroje a principy jejich činnosti, s čímž samozřejmě souvisí i jejich vlastnosti. Vzhledem k tomu, že jejich základním blokem jsou analogově-číslicové popř. číslicově-analogové převodníky, je samostatná kapitola věnována i digitalizaci signálu. Problematika určování nejistot měření je klíčovým parametrem při řízení a kontrole kvality výroby. Nejistotám měření je proto věnována nejen celá 1. kapitola, ale odhad nejistot je také zmíněn i v kapitolách věnovaným metodám měření aktivních elektrických veličina parametrů pasivních součástek.
The effect of conductor permeability on electric current transducers
In this paper, experimental works and theoretical analysis are presented to analyze the influence of the conductor permeability on the precision of yokeless current sensors. The results of finite-element method (FEM) fit well the measured field values around the conductor. Finally we evaluate the difference in magnetic fields distribution around non-magnetic and magnetic conductor. The calculated values show that the permeability of the ferromagnetic conductor significally affects the reading of the electric current sensors even at DC.
A COMPARISON OF DC AND AC METHODS FOR CALIBRATION OF SEARCH COILS WITH A HIGH AREA TURNS VALUE
Search coils are widely used for measuring AC magnetic fields, and in special cases for measuring DC magnetic fields with the webermeter and for comparing magnetic flux density standards and magnetic flux standards. This paper compares the measuring equipment that is used and the accuracy that can be achieved by known DC and AC methods for calibrating search coils with a high area turns value.
Magnetic Heating by Silica-coated Co-Zn Ferrite Particles
This study is aimed at the preparation of silica-coated nanoparticles of cobalt–zinc ferrite and their heating properties with respect to potential application in magnetic fluid hyperthermia. The magnetic cores of Co0.4Zn0.6Fe2O4+γ possessing two different sizes were prepared by the coprecipitation method followed by annealing and mechanical treatment. The subsequent encapsulation of the samples by silica led to colloidally stable suspensions in water.
Calibrations of Phase and Ratio Errors of Current and Voltage Channels of Energy Meter
Sensors & Their Applications XVII. Bristol: IOP Publishing Ltd, 2013, pp. 1-5. Journal of Physics Conference Series. ISSN 1742-6588. Available from: http://iopscience.iop.org/1742-6596/450/1/012046
This paper deals with measurement of phase and ratio errors of current and voltage channels of a new produced energy meter. This fully digitally controlled energy meter combines the classical static energy meter with power quality analyzer. The calibration of phase and ratio errors in wide frequency range is then necessary. Paper shows the results of error measurement, introduces the mathematical approximations and describes the calibration constants. It allows error compensation and power calculation of particular harmonics. The electric power of the higher harmonics can be interesting information of distributed electric energy quality.
Frequency Analysis of DC Tolerant Current Transformers
This article deals with wide frequency range behaviour of DC tolerant current transformers that are usually used in modern static energy meters. In this application current transformers must comply with European and International Standards in their accuracy and DC tolerance. Therefore, the linear DC tolerant current transformers and double core current transformers are used in this field. More details about the problems of these particular types of transformers can be found in our previous works. Although these transformers are designed mainly for power distribution network frequency (50/60 Hz), it can be interesting to understand their behaviour in wider frequency range. Based on this knowledge the new generations of energy meters with measuring quality of electric energy will be produced. This solution brings better measurement of consumption of nonlinear loads or measurement of non-sinusoidal voltage and current sources such as solar cells or fuel cells. The determination of actual power consumption in such energy meters is done using particular harmonics component of current and voltage. We measured the phase and ratio errors that are the most important parameters of current transformers, to characterize several samples of current transformers of both types.
Magnetic Nanoparticles for Therapy and Diagnostics
The research and utilization of the magnetic nanoparticles in, e.g., biology and medicine have been preferentially oriented on magnetite Fe3O4 and maghemite γ-Fe2O3. The complex oxides allow a better control of the magnetic properties in a desirable way. We demonstrate this approach on an example of the La1-xSrxMnO3 perovskites from the point of view of their use in self-controlled magnetic fluid hyperthermia and increase of contrast in magnetic resonance imaging. With materials possessing suitable values of transition temperature TC, coercivity and magnetization, the heating power generated by the nanoparticles was estimated by two independent methods and they were finally employed in vitro and in vivo hyperthermia experiments.
Effect of Half-wave Rectified Current on Readout of Energy Meter
Paper deals with effect of half-wave rectified current on the measurement in energy meter. This type of current can be normally present in distribution network and does not cause any problem in active energy consumption measurement. On the other hand it can be the cause of saturation of the high permeability core of dual core current transformers. Moreover half-wave rectified current brings the increasing of the reactive power and consequently also the apparent power. It causes rising of losses in the conductors. The simple energy meter, eg electromechanical, does not measure these values and the losses are hidden. In present day there are many problems with capacity of energetic distribution network. Therefore information about character of energy consumption can be very important.
We analyze the Influence of extemal "unclamped" currents on contactless current sensors, especially the gradient sensor arrays and the current clamps. Best suppression of close currents can be achieved by using magnetic yoke with optimized shielding. DCIAC fluxgate current clamps of our design have low perming error and suppress externa' current by the factor of 20 000.
MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE SENSITIVITY AND ORTHOGONALITY OF A TRIAXIAL VECTOR MAGNETOMETER
The temperature dependence of the sensitivity and orthogonality of a tri-axial vector magnetometer is measured with the use of a dedicated thermostatic system and a non-magnetic positioning platform. The dependency is obtained from the results of repeated scalar calibrations for different temperatures.
We analyze the influence of external "unclamped" currents to contactless current sensors, especially the current clamps. Best suppression of close currents can be achieved by using magnetic yoke with optimized shielding. DC/AC fluxgate current clamps of our design have low perming error and suppress external current by the factor of 20 000.
The Magnetic and Hyperthermia Studies of Bare and Silica-coated La0.75Sr0.25MnO3 Nanoparticles
Kaman, O., Veverka, P., Jirák, Z., Maryško, M:, Knížek, K., Veverka, M., doc. Ing. Petr Kašpar, CSc., Burian, M., Šepelák, V., Pollert, E.
Journal of Nanoparticle Research. 2011, 13(3), 1237-1252. ISSN 1388-0764.
The magnetic nanoparticles with a controlled size were prepared. The selected cores were encapsulated into silica shell. The heating experiments were carried oud in an AC field od frequencies 100kHz - 1MHz.
Compact Fluxgate Sensor with a Vector Compensation of a Measured Magnetic Field
Compact tri-axial fluxgate sensor which combines new materials, traditional ring-core topology and vector field compensation is introduced. Magnetometer construction and preliminary results are discussed.
Hybrid La(1-x)Sr(x)MnO(3) Nanoparticles as Colloidal Mediators for Magnetic Fluid Hyperthermia
Pollert, E., Kaman, O., Veverka, P., Veverka, M., Maryško, M., Závěta, K., Kačenka, M., Lukeš, I., Jendelová, P., doc. Ing. Petr Kašpar, CSc., Burian, M., Herynek, V.
Philosophical Transactions of the Royal Socxiety A - Mathematical, Physical and Engineering Sciences. 2010, 10.1098(368), 4389-4405. ISSN 1364-503X.
Hybrid nanoparticles consisting of La0.75Sr0.25MnO3 cores covered by silica were synthesized by a procedure consisting of several steps, including sol-gel method in the presence of citric acid and ethylene glycol, thermal and mechanical treatment, encapsulation employing tetraethoxysilane and final separation by the centrifugation in order to get a required size fraction. Morphological studies revealed well separated particles which form stable water suspension. Magnetic studies include magnetization measurements and investigation of the ferromagnetic - superparamagnetic - paramagnetic transition. Magnetic heating experiments in a "calorimetric mode" were used to determine heating efficiency of the particles in water suspension and further employed for biological studies of extracellular and intracellular effects analyzed by the tests of viability.
Weak Points of Current Sensors in Static Energy Meters
The energy meters with dual core current transformers, that measure energy consumption of inductive or capacitive load and DC magnetic flux is present in the core, measure with the errors up to few tens of percentage. It is due to saturation of high permeability and it causes the step change of phase displacement. This change in dependence on the distance between permanent magnet and current transformer can be up to tens of degrees. The article deals with these errors and shows them in dependence on the type of load.
Automated System for the Calibration of Magnetometers
Automated non-magnetic calibration platform with three axes of freedom is presented. Main applications are scalar calibration of vector magnetometers and accelerometers and testing of their assemblies (e.g. an electronic compass).
Calibration of a Triaxial Fluxgate Magnetometer and Accelerometer with an Automated Non-magnetic Calibration System
A method, instrumentation used and results of calibration and testing of tri-axial magnetometers, accelerometers are presented. The method is based on a scalar calibration technique with the use of an innovative computer controllable non-magnetic platform. The speed, precision, comfort and repeatability of the measurement are superior to techniques which use hand-driven tools.
Detection of Disturbance of Working Conditions of Current Transformer in Energy Meters for Reduction of Unauthorized Current Consumption
Current transformers can be very easily affected by dc component of measured current. The behavior of such transformers can be different in comparison with normal conditions. The errors of power measurements arise in order of units of percent and can be both positive and negative according to the type of load for some type of current transformers. The errors are mainly caused by change of phase shift between primary and secondary current.
The source of the problem is dc magnetic flux in the ferromagnetic core of the current transformer. The presence of dc magnetic field in ferromagnetic core of current transformer can be, in some cases, detected by analyzing the frequency spectrum of current signal using a microcontroller, usually by measuring the second harmonic. According to these results the energy meter is able to decide about possibility of unauthorized current consumption.
Drawback of Using Double Core Current Transformers in Static Watt-Hour Meters
This article deals with dual core current transformers that are used in some modern static watt-hour meters where they should substitute the more expensive DC tolerant current transformer with linear hysteresis loop. It describes the problem of power consumption measurement on inductive or capacitive loads where some DC magnetic field is applied. In this case the core with high permeability is saturated and operating point is moved on hysteresis loop of low permeability core. Then additional errors occur and the sign of the error can be both positive and negative depending on load type. Dimension of errors can be in order from units up to tens of per cents and it relies on power factor and DC magnetic field. Explanation of this problem is described in the article as well as some results of measurements and comparison with theoretical computation.
Silica Encapsulated Manganese Perovskite Nanoparticles for Magnetically Induced Hyperthermia without the Risk of Overheating
Kaman, O., Pollert, E., Veverka, P., Veverka, M., Hadová, E., Knížek, K., Maryško, M., doc. Ing. Petr Kašpar, CSc., Klementová, M., Grünwaldová, V., Vasseur, S., Epherre, R., Mornet, S., Goglio, G., Duguet, E.
Manganese perovskite nanoparticles of the composition La0.75Sr0.25MnO3 uniformly coated with silica were prepared by encapsulation of the magnetic cores (mean crystallite size 24 nm) using tetraethoxysilane followed by fractionation. Resulting hybrid particles form a stable suspension in aqueous environmentat at physiological pH and posses a narrow hydrodynamic size distribution. Both calorimetric heating experiments and hysteresis loops in the alternating field revealed high specific power losses, further enhanced by the encapsulation procedure in the case of the coated particles. The corresponding results are discussed on the basis of complex characterization of the particles and especially detailed magnetic measurements. Moreover the Curie temperature (335 K) of the selected magnetic cores resolves the risk of local overheating during hyperthermia treatment.
Drawback of Using Double Core Current Transformers in Static Watt-hour Meters
The current transformers in modern static watt-hour meters have to fulfil the criteria according to international standards. The manufacturers of the transformers use various techniques to obtain high DC tolerance. Some of them use the cores with low permeability and narrow and almost linear BH loop. These transformers are quite expensive and therefore some manufacturers use the double cores made from high and low permeability material. But as was found these transformers could bring additional errors in special conditions. The paper describes these conditions and explains the problems.
Non-Magnetic Platform for Scalar Calibration of Magnetometers
A complete system for scalar calibration of magnetometers is being introduced in this article. The main part of the system is an absolutely non-magnetic mechanical platform which is driven by piezoelectric motors. Together with the electronic control unit and software equipment it forms a unique system for on-site scalar calibration of spacegrade magnetometers. The parameters of the calibration system and experiences obtained during the construction phase are presented.
The Phase Displacement of DC Tolerant Current Transformers under DC Biasing
The most of the electronic static energy meters employ current transformers for current sensing. The current transformer has to fulfil some requirements according to international standards. Accuracy, together with the immunity against the dc current, is one of the requirements. Therefore manufactures of energy meter use the dc tolerant current transformers with linear hysteresis loop. These types of sensors have constant parameters and behaviour in very wide range of dc biasing. Second type of current transformers employs two cores with different parameters. But the parameters and behaviour vary with dc biasing. This paper deals with the changes of phase error of current transformers under dc biasing and describes the consequences of these changes.
The Precision of Gastric Motility and Volume Sensing by Implanted Magnetic Sensors
Characterization of ferromagnetic materials in the form of powders and dusts is required in many practical applications. Among them are biomedical applications like magnetopneumography and magnetic hyperthermia. In both cases, specific problems make the accurate measurement difficult. We describe the practical experience with static and dynamic characterization of powder specimens.
Current Sensors Suitable for Using in Electricity Meters
ICST 2007 - The 2nd International Conference on Sensing Technology. Palmerston North: Massey University, Institute of Information Sciences and Technology, 2007. pp. 519-522. ISBN 978-0-473-12432-8.
This article introduces the current sensors that are used in electricity meters. It shows their advantages and disadvantages. This paper is especially focused on DC tolerant current transformers and how they can be influenced by the DC component of measured current. Moreover the effect of a strong magnetic field generated by permanent magnets is analysed. Method to eliminate the disturbance and the stealing of energy is then presented. Next, the article deals with Rogowski coils and how it can replace the current transformers in electricity meters. Finally the problem of manufacturing precise coils, suitable for measuring the current in order of tens mA as it is required by the distributors of electrical energy, is presented.
DC Gradiometers for Bomb Detection: Scalar Versus Vectorial
Gastric electrical stimulation has shown positive effects on weight reduction and on various gastric motility disorders. This stimulation leads to earlier satiety thus decreasing food consumption significantly. For long term effective function some control of implant activity is necessary, for which gastric volume and movements have to be sensed. For this purpose we have chosen mutual induction principle between small implantable coils. Sensors have to fulfill many requirements including biocompatibility, mechanical and chemical durability and minimum power consumption. First successful in-vivo experiments were held with simple configuration of two implantable coils and an external electronics box.
In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mössbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature.
Magnetic Properties of Nanoparticles of Co Ferrite in AC and DC Magnetic Fields
Magnetic micro- and nanocomposites are prospective materials also for biomedical applications in diagnostics and therapy, among them for local destruction of unwanted, eg, cancer cells by magnetic fluid hyperthermia. With this purpose in mind we studied magnetic behaviour of the nanoparticles of Co ferrite in both dc and ac fields.
Measurement of Ratio Error and Phase Displacement of DC Tolerant Current Transformers
DC tolerant current transformers are used in modern electricity meters. This brings some advantages but at the same time increases ratio error and causes higher but almost constant phase displacement. Therefore it is important to measure both errors.
The indirect method of these errors measurement the errors has been tested on a commercial DC tolerant current transformer with manufacturer declared errors and the calculated errors were in very good accord with the declared parameters. This way the verify of the indirect method was proven and it has been used for further measurements. The measurements have been done with four DC tolerant current transformers that use cores made by different manufacturers. This article describes the method of measurement and shows the results.
New Tc-tuned Magnetic Nanoparticles for Self-controlled Hyperthermia
Manganese perovskite nanoparticles of the XRD size in the range of 30 - 49 nm were synthesized via sol-gel technique employing citric and ethylene glycol. Their magnetic properties were investigated in the static and alternating magnetic fields. Partivular attention was paid to the relation between the size of particles and resulting magnetic power losses, measured by the calorimetric heating experiments on the stable water suspensions and of the hysteresis loops in the alternating fields on powdered samples.
Application of Fluxgate Gradiometer in Magnetopneumography
Two main errors exist in the current transformers: the ratio error and the phase displacement. These errors indirectly depends on apparent permeability of the ferromagnetic core. Precise current transformers usually use a core with high apparent permeability which ensures small errors. But even a small DC component of the measured current causes saturation of the core and growing errors. Therefore the cores with low permeability, narrow and almost linear hysteresis loop are used in the current transformers in the modern energy meters. This paper examines DC tolerance and its influence on the errors of the current transformer and describes the method of its measuring.
The article deals with fully digital compass based on AMR sensors and accelerometers. The developed device gives information about actual azimuth, roll and pitch. The article is especially focused on errors caused by sensors misalignment, cross-axis effect and temperature offset drifts of the sensors.
Measurement of Ratio Error and Phase Displacement of Current Transformers
The current transformers are used in almost all energy meters. Therefore it is important to know about their ratio error and phase displacement. Two ways can be used for measurement both of the errors. The direct method consist in comparison of the measured current transformer with the standard current transformer. The indirect method uses a measurement of magnetizing current and computation the errors from its value. This article deals with the indirect method and its using with measurement on DC tolerant current transformers that are presently used in the energy meters.
On-demand gastric electrical stimulation has been proposed to save energy of the pacing implant. For the purpose of control enough information about movement and size of stomach has to be measured with minimum external parts. Higher long-term efficiency of the method is expected in addition to its formerly documented positive effects in obesity treatment. Magnetic induction principle was chosen to measure the elongation of gastric wall between attached coils. In vivo a simple two coil configuration has been successfully tested and satisfactory resolution in demanded bandwidth has been proved. Especially for experimental studies directional dependence may be compensated by multi-axial sensor.
AMR Navigation Systems and Methods of their Calibration
The design of a navigation system with AMR and accelerometers is described in this article. The calibration methods of general triaxial sensor systems are discussed in this article and basic results are presented. The application of these calibration methods for developed navigation system is also included in this article.
Magnetopneumography (MPG) serves for examination of human lungs exposition to ferromagnetic dusts and fumes (e.g. in metal-workers in industry) through measurement of remanent magnetic field after magnetization of the subject in an electromagnet. Fluxgate gradiometer is used for measurement and various methods (neural networks, etc.) are used for evaluation and estimation of the inhaled dust amount and distribution.
New PCB (Printed Circuit Board) technology flat fluxgate sensor with integrated coils and amorphous alloy core was developed and its excitation parameters were optimized for low-power consumption. The power consumption achieved with 10 kHz, 300 mA p-p pulse excitation with duty cycle 12.5 % was only 3.9 mW, which is 3-times lower than that for sinewave flux density excitation. The sensor sensitivity reached 94 V/T.
Navigation System with Magnetometers and Accelerometers
Analog multipliers comprising the Hall sensors have been used in electronic design, typically in powermeters. This article summarizes the results of experiments performed with a commercially available anisotropic magnetoresistive (AMR) sensor, used for the same purpose. The on-chip compensation coil can be successfully used in the function of the "current clamps" of the wattmeter. Periodical re-magnetizing (flipping) of the sensor structure performed by the flipping coil can improve the device parameters. This paper is not a description of a functioning, practice-ready device. It reports an experiment showing the feasibility of AMRs in the area of power measurements.
AMR Navigation Systems and Methods of Their Calibration
The article deals with fully digital navigation system and method of its calibration using rotation in roll. The system calculates actial azimuth, roll and pitch from measurement of Earth's magnetic and gravitational filed vectors. Then the calculated azimuth is not influenced by actual roll or pitch.
AMR Navigation Systems and Methods of Their Calibration
The article deals with fully digital navigation system based on AMR sensors and MEMS accelerometers. Described are used calibration methods: scalar calibration for finding sensitivities, offsets and non-orthogonalities and rotation in roll and azimuth for finding angular deviations (misalignments) of the sensor coordinate systems.. The device calculates actual azimuth, roll and pitch from measurement of Earth's magnetic and gravitational field vectors. Then the calculated azimuth is not influenced by actual roll or pitch.
Commercially available AMR sensors can be used as simple analog multiplier devices, which can be used in real (active) electric power transducers. The electronics of such a device need not be complicated, when using the on-chip integrated coils. Periodical re-magnetizing (flipping) of the sensor structure can improve the device parameters.
AC Characterization of Materials for Fluxgate Cores
Na geodetické laboratoři Pecný a Fakultě elektrotechnické ČVUT byly koncem roku 2001 provedeny magnetické zkoušky gravimetrů LaCoste a Romberg typu G, č.137, č.176, č.1068. Pro měření bylo použito umělé magnetické pole vytvořené pomocí Helmholtzovy cívky. Vztah mezi záznamem gravimetrů a magnetickým polem byl určen pro horizontální i vertikální složku vektoru magnetické indukce. Byly zjištěny rozdíly mezi citlivostí jednotlivých gravimetrů na změny magnetického pole a především u gravimetrů č. 137 byla prokázána výrazná závislost na magnetickém poli. Třicetinásobné snížení tohoto rušivého vlivu bylo dosaženo umístěním gravimetru do permalloyového válce NiFe 76. Průběh magnetického pole v gravimetrické laboratoři na GO Pecný byl zjištěn měřením pomocí tříosého magnetometru.
GMI effect in permalloy can be used to measure DC magnetic fields. Impedance change of 50% at a field of 0.5 mT was observed at 200 kHz frequency. Magnetometer using biased two-stripe 10-cm long sensor achieved 10% linearity in open loop and 1% hysteresis error in the +/-80 uT range.
Precise Magnetic Sensors and Magnetometers for Military and Space Applications
Digital hysteresisgraph can be used for the measurement of dynamic hysteresis loops up to 100 kHz. Digital feedback allows achievement of sinusoidal flux density by iterative modification of the excitation voltage waveform. This approach is used for the measurement of closed (toroidal) samples at higher frequencies.
ČVUT se opakovaně stalo úspěšným nositelem vzdělávacích evropských projektů. V rámci tříletého pilotního projektu (1.12.2000-30.11.2003) "Modulární kurzy moderních senzorů", podporovaného programem Leonardo da Vinci Evropské unie (CZ/PP-134026), vytváří 9 partnerů z 8 evropských zemí výukové materiály pro prezenční i distanční výuku moderních senzorů v různých úrovních odbornosti a v několika jazycích. Naše pracoviště je koordinátorem celého projektu, druhým partnerem z ČR je Škoda Auto. Celkový rozpočet projektu je 597940 EUR, z toho příspěvek Evropské unie činí 398749 EUR ((pro ČVUT 76000 EUR). Partnery projektu jsou: VIA, ČVUT, ŠKODA, BFW, ICT, IDEC, M2A, ZSE, DCU.
Calibration of Triaxial Magnetometers by Theodolite
Although AMR and GMR sensors gradually penetrate many industrial applications, Hall sensors
still remain the most widely used solution. However, developersof modern systems often require
more added value than just plain sensor in order to satisfy specific needs in their construction.
The construction of temperature testing system is described. The description covers temperature chamber, cooling and heating system, testing methodology and complete testing system with computer control.
Digital dynamic hysteresisgraph for measurement in DC to 100 kHz frequency range was developed in out department. Among the errors influencing the measurement are also the phase shifts. This contribution deals with determination and software compensation of these phase shifts.
Feromagnetický prach usazený v plicích svářečů, brusičů a horníků z některých rudných dolů může být detekován měřením remanentního pole po stejnosměrném zmagnetování. Tato neinvazivní metoda se nazývá magnetopneumometrie. Tento příspěvek popisuje, jakým směrem se ubíral výzkum v této oblasti od r.1998 a jakých výsledků bylo dosaženo na katedře měření FEL ČVUT.
New Measurement and Calibration Methods of Electrical Quantities and Instruments. Budapest: IMEKO TC4 Technical Committee on Measurement of Electrical Quantities, 1996, pp. 141-144. ISBN 963-420-491-0.
New Measurement and Calibration Methods of Electrical Quantities and Instruments. Budapest: IMEKO TC4 Technical Committee on Measurement of Electrical Quantities, 1996, pp. 88-91. ISBN 963-420-491-0.