Particular Issues Associated with Performing Meterage Through the Use of Magneto Therapy Devices

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Particular Issues Associated with Performing Meterage Through the Use of Magneto Therapy Devices 1 Y.S. Lapchenko1,a, V.Y. Denysiuk1,b, V.V. Krasovski1,c, V.P. Symonyuk1,d 1 – Lutsk National Technical University, Lutsk, Ukraine a – y.lapchenko@lntu.edu.ua b – v.denysiuk@lntu.edu.ua c – vlkras@i.ua d – v.symonyuk@lntu.edu.ua DOI 10.2412/mmse.91.41.874 provided by Seo4U.link

Keywords: magneto therapy, inductor, magnetic induction, electronic oscillograph, electromotive force, transducer.

ABSTRACT. This article describes the features of the measurement of magnetic parameters of magneto therapy devices.

The following measurement of magnetic induction of a continuous magnetic field, the magnetic induction of the sinusoidal magnetic field. Also describes the inductive method of measuring a variable magnetic induction of the sinusoidal and non-sinusoidal of the magnetic field.

Introduction. Magnetic fields which are used in magneto therapy and magneto biology, generally are inhomogeneous and limited in volume, they are distinct in the variety of parameters. Thus, the magnitude of magnetic induction can range from fractions to hundreds milliteslas; the fields can be continuous and variable/alternating (sinusoidal, rippled, pulsed), they are characterized by various frequencies and waveform of the currency that goes through the inductor. At this variety of parameters, relevant industrial metering devices can scarcely ever be found. However, even if they are available, the process of measurement and obtaining a result is quite time-consuming. Firstly, it is related to the fact that key parameters of the magnetic field, magnetic induction and its gradient, are vector quantities and must be estimated not only in magnitude (module), but also in orientation.

Transducers, which respond to the direction of a vector, are used for metering quantities. That kind of transducer must be compact, much smaller than the field action area, because the induction aggregates throughout the transducer [1].

Research results. For the convenience of use and the increase of mechanical performance, the transducer along with the connected wires are usually mounted in an applicator which is a thin plastic plate considerably more long than wide, and is sufficient for manipulating.

Using a step-by-step approaching during the process of metering, a place where a vector of magnetic induction vertical to the surface of the transducer is found, which is shown by a maximum value of a device attached to it. In the process of magnetic induction metering on the surface of the magnetic field source, an applicator is attached against this surface. Taking into account that magnetic field is inhomogeneous, when magnetic induction and its gradients are in nearly, yet surrounding points, they can fundamentally differ depending on the type of source (constant magnet, solenoid, electromagnet), its configuration (the form of section, correlation of crosswise size and longitudinal size), and dimensions, metering result is valid only to the point at which it is received. In other words, the results of metering parameters of the field must be snapped to coordinate grid.

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

When it comes to commercialization, as the identity of magneto therapy device’s design is provided with a set of production documents, for the purpose of electrics and background data control, it is sufficient to check magnetic induction in one pre-selected point, usually near the poles or at the axis of symmetry. However, this value, which is usually brought in the device configuration, is not only deficient for the characterization of inhomogeneous magnetic field intensity, but in fact it does not let assess the field and cannot be used in describing an operative factor or while attempting to reproduce it. In order to characterize inhomogeneous field (while the homogeneous field in magneto therapy devices should be considered as an exception), it is needed to “snap” an image of magnetic field in the coordinate grid, which makes possible to assess the value of magnetic induction, its gradient and the direction in the centre of an action or in other studies area. The metering can be done once at any moment before or after treatment or experimentation, without a patient, in the air, and they will stay the same in the volume of biological object placed into the field, because living tissues are transparent for low-frequency magnetic field. So simplifies the metrological assurance in magneto therapy and magneto biology.

Getting started metering in variable magnetic field, it is necessary to know the current waveform that supplies the inductor. Industrial gauges are usually designed for continuous field or a field that varies in accordance with the law and approaches sinusoidal. Upon these and other laws of field alteration, different methods of metering are used, one of which is inductive.

In magneto therapy and magneto biology the intensity of variable field is usual to characterize by peak value of magnetic induction and its gradient. But industrial teslameters are standardized at the average (half-period average) or effective values (root-mean-square). The relation between amplitude (Ваm), average (Вav), and effective (Вe) values for some curves (fig. 1). They are in line in sinusoidal and pulsating double-wave curves, for which:

Bam  1,414Be  1,571Bav ,

(1)

and differ in pulsating half-wave curve:

Bam  2Be  3,142Bav .

(2)

Fig. 1. The relation between amplitude (Ваm), average (Вav), and effective (Вe) values for sinusoidal wave (a), pulsating double-wave curve (b), and pulsating half-wave curve (c): Т – period of variation; Т0 – length of half wave.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

In the general case, but with the increase of the correlation of the period of variation (Т) to the length of the half wave (Т0), the average and effective values decrease. Consequently, the result of pulsed magnetic field metering depends on the selection of value even more. Depicting magnetic induction of variable field, it should be necessarily indicated which value is the question, amplitude, effective or average.

Background noise (induction) affects the magnetic measurements significantly. If the source of magnetic field is absent, or at the long distance from it, and the device’s figures on the chosen scale differ from zero, the time of metering is changed, performs in another room or shielded cabin.

Industrial Magnetometers and the Scope of Their Use. General Characteristic. Our country does not produce devices that are intended for metering the intensity of non-sinusoidal variable fields, including pulsing and pulsed, and does not have industrial gauges for metering the gradient of magnetic induction at all. The major measure of inaccuracy is introduced, consequently, it belongs to the bounds of metering. For this reason, the measure of inaccuracy rises greatly at the distance from the end of the scale, and the first third of pointer-and-scale instruments is not in use generally.

Additional gauging errors are connected not only with the influence of the environment (temperature change, irrelevant magnetic fields etc.), but in many ways with the procedure of metering: with final dimensions of the transducer, inexactness of defining its place in the applicator, and, therefore, on the coordinate grid in the effective magnetic field action area, the aberration of the surface from the point which is perpendicular to the vector of magnetic induction, instability of the device’s figures, and, of course, the operator’s qualification. They can by many times exceed the main inaccuracies that are specified in the device’s description.

Magnetic Induction of Continuous Field Detectors. Magnetic field intensity is defined through the use of any magnetic induction detector which has a suitable scale, or using webermeters completed with metering coils. The limits of magnetic induction detecting through the use of webermeter are calculated according to a formula:

B  (10  ) / S K , mT where Ф – is a limit of webermeter’s detection, µWb; Sk – is a constant of metering coil, sm2.

Constant can not be increased randomly:

S K  wS , sm2,

(3)

It is explained by the fact that, on one side, the square S of the coils’ form of the section is limited, as a transducer should be compact, and, on the other side, for each webermeter there is a higher limit of coil resistance, so, the number of coils w cannot be arbitrarily large. It is well to bear in mind that the work with the webermeter puts some trouble, because the counting is carried out taking into account the difference of device’s figures, and the indicator “drags”.

Thus, the most casal and the least time-consuming is metering the magnetic field intensity using industrial magnetic field detectors. The intensity of continuous field can be defined through the use of industrial webermeters completed with the produced by the consumer, and those that have been metrologically checked with measuring coils.

Magnetic Induction of Sinusoidal Fields Detectors. To select the most appropriate teslameter which is intended to define variable field magnetic induction, inductor’s power current waveform and MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

its frequency must be acquainted, and in some cases a harmonic factor. An oscilloscope, a frequency meter and a distortion-factor meter are used to determine them [2].

Teslameters which are designed to work in a variable magnetic field, within all borders are suitable to measure induction of a sinusoidal field of 50 Hz. Allowable frequencies different from 50 Hz, as well as inaccuracies depend on the chosen metering borders. Thus, for example, through the use of milliteslameter Ф4356 within 0,1 and 0,3 mT it is possible to determine induction with 10% inaccuracy in the whole audio-frequency range, and on other borders the metering inaccuracy decreases, but the allowable frequency range is remarkably narrowed down.

Teslameter conforming to the waveform and current frequency, may also need limits of metering, which can be finalized when the value, wherein the scale is graduated – average, effective or amplitude – is known, because according to this, the limits of metering may change by a factor of 1,5.

Thus, the scales of Ф4356 are graduated upon the average values. For the purpose of enumeration into normally used amplitude values, it is necessary to multiply the device’s readings by a coefficient of 1,57 according to the formula (1), and in this way in amplitude values the limits of measurement of this device will be from 0,157 to 157 mT rather than nominal 0,1-100 mT. Unlike the device Ф4356, microteslameter Г79 shows true values which can be enumerated into amplitude by multiplying according to the formula (1) by a coefficient 1,41. So, within amplitude values the limits of metering of the device are 0,14 µT-1,4 mT instead of nominal 0,1 µT-1 mT. Thuswise, industrial devices allow to define an amplitude value of the intensity of sinusoidal field approximately from fractions of µT to 150 mT with the frequency 400 Hz, and to 1,4 µT in audiofrequency range.

Inductive Method of Metering Variable Magnetic Induction. Particular Issues Associated with Induction Method, and Major Connections. Owing to the lack of industrial devices, it is often necessary to use specific methods of metering. The intensity of variable magnetic field can be defined in two different ways: ferroprobe, which is based on the Hall Effect of Faraday Effect, inductive, etc.

Ferroprobe transducers, as a rule, are designed for magnetic field metering up to 10 mT, they are unappropriated to define the intensity of the field different from sinusoidal. Hall probe needs special power sources, and their parameters are very temperature-dependent. Implementation of Faraday method is associated with complex hardware, and is advantageous for studying magnetic fields, the intensity of which exceeds the intensity used in medicine greatly. Besides, corresponding Hall and Faraday probes are not always available [3].

Inductive method can be comparatively easy implemented at metering the intensity of variable field in the wide range of magnetic induction values and frequency. The method is based on using the law of electromagnetic induction: electromotive force that appears in the coil when put into the variable magnetic field is analyzed. Thus, metering coil is used as a transducer of magnetic values into electrical. The benefits of inductive method are stipulated by the ability to make a metering coil with the necessary dimensions and constant Sk in the laboratory, as well as operational comfort, high overload ability, and no temperature dependence. For the implementation of inductive method, there is no need in additional power sources, and metrological examination is limited by the definition of constant Sk. Metering coil and its outputs which at the process of metering are connected with the input of an electronic voltmeter or integrating circuit, are usually mounted on a flat applicator. Maximum values of the voltmeter are received providing that magnetic induction vector is parallel to its axis and, consequently, is perpendicular to the surface of the applicator.

If such a coil is put into a variable field in induction B, electromotive force

E (t )  S K  Bn / t ,

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(4)

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

is proportional to derivative Bn / t and, therefore, magnetic induction В can be determined by the result of integration E (t ) .

Sometimes when the law of variation is known as, for example, in sinusoidal field, magnetic induction is derived from differentiation operator, and with the purpose of its definition, it is sufficient to determine E (t ) .

Magnetic Induction of Sinusoidal Field Metering. In the sinusoidal magnetic field the amplitude of magnetic induction in accordance with the expression (3) is counted on formula:

Bam  Eam / 2fS K .

With the purpose of metering sinusoidal electromotive force, any electronic voltmeter is attached to the ends of the metering coil (fig. 2, а). As the scale of the voltmeter is normally graduated in effective values, we change the amplitude value of electromotive force into the effective value. Then, taking into account the expression (1), we get

Bam  Ee  10 4 / 4,44  fS K  2250  Ee /( fS K ) , mT,

(5)

and with frequency of 50 Hz

Bam  45 Ee / S K , mT,

(5а)

where Sk – is a constant of metering coil, sm2; f – is a frequency, Hz;

E e – is an effective value of electromotive force, mV. If the scale of being used voltmeter is graduated in amplitude or average values, which is rare, for the purpose of the evaluation by formula (5) they are changed into effective value:

Ea  0,707  Eam or Ea  1,11  Eav .

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(6)

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 2. Variable magnetic induction measurement in sinusoidal field by inductive method (а); in non-sinusoidal field using capacitive integrator (b), V – voltmeter.

As a consequence of the formula (5), the responsiveness of the device which is defined by the capacitive integrator (the ratio of induction effective electromotive force to the amplitude value of the defined magnetic induction), can be in general introduced as fSk/2250 mV/mT, and with the frequency of 50 Hz – Sk/45 mV/mT. It is evident that when magnetic induction B and frequency f are unchangeable and the constant of measuring coil Sk rises, the responsiveness of the device and electromotive force value Е undergoes a rise. Consequently, under a weak magnetic field of low frequency metering, there is a need of a coil with a quite large constant. Thus, if to consider that the least positive reference of electronic millivoltmeter is 20 mV (the reference at which the urban laboratory can ignore background noise), so based upon formulas (5) and (5, a), it comes out that for the purpose of metering 10 mT field with the frequency 50 Hz, the constant of the coil must be not less than 90 sm2, and with 5 Hz frequency – not less than 900 sm2.

Magnetic Induction of Non-Sinusoidal Variable Magnetic Field Metering. When it comes to metering a non-sinusoidal variable field through the use of magnetic induction method, and electromotive force is related to the derivative of magnetic induction according to formula (4), and for the purpose of magnetic induction measurement a capacitive integrator with capacity (C) on the output is used (fig. 2, b). In the effect that integration is being performed with relatively small distortion, active resistance R should be much more than reactive resistance I / C , and for pulsed signal, the time constant RC should be much more than pulse durationа τі, so it is necessary that

RC  1 or RC   im

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(7)

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

In these conditions, the amplitude of the magnetic induction can be calculated by the following formula:

Bam  RCU a  10 4 / S K , where R – active resistance, kOhm; С – capacity, µF; Sk – coil constant, sm2; Ua – peak output voltage, mV. If capacitive integrator is correct according to (7), valid waveform of magnetic field alteration that was distorted by differentiating on the metering coil, is restored on the output. To control the form of integrated electromotive force, electron oscillograph is used, upon that its vertical plates are connected to the capacity С in parallel (fig. 2, b). The comparison of the form of an integrated waveform with the form of inductor current waveform is convenient to make using dual beam oscilloscope.

Strict observance of the condition (7) includes in a substantial decrease of output voltage, so it can be comparatively inconsiderable against noise which is sensibly detectable on the scale of 10 mV. In some instances to increase electric potential Ua coils with constant Sk are used, which go far beyond 1000 sm2.

Example. If the frequency of pulsation is 50 Hz, time length of pulsating impulse is 1/(50·2)=0,01 s and RC≫0,01 s is necessary. This condition is fulfilled, for instance, when С=10 µF and R=30 kOhm (RC=0,3 s). If in such case the constant of measuring coil Sk=600 sm2, then Bam=0,3·Ua·104/600=5·Ua, mT, with calibration constant 0,2 mV/mT. Then at magnetic induction measurement 40 mT Ua is only 8 mV, which does not provide accurate results. If the coil is changed to the one with constant Sk=1500 sm2, then Bam=0,3·Ua·104/1500=2·Ua, mT, with calibration constant 0,5 mV/mT, and with the same magnetic induction Ua=20 mV, which is allowable.

Measurement of no-sinusoidal alternating current is done through the use of electronic oscillograph.

The Use of Electronic Oscillograph. If in the context of studying the magnetic field there is a need to determine the variation of its intensity or the amplitude of non-sinusoidal signal, low-frequency or impulse (when the pulsing field is studied) electronic oscillograph is used. Working with oscillograph, a horizontal scan is usually in the position when two-three periods of the studied waveform are on the screen, and with the aid of vertical scan and base-line drift it is necessary that the maximal range of the image covers the largest screen area, but is within the working area, its lineal part (it is about 80-90% of the vertical scale of electron-beam tube).

To control the form of the current waveform, voltage power supply is connected to vertical plates of the oscillograph. To control the form of current waveform or when powered by direct current, within the aim of defining pulsation coefficient, the circuit of the inductor is interrupted (the power supply should be turned off in advance!), low-value resistor with resistance r is switched in steps with the inductor, and its ends are connected to vertical plates of electronic oscillograph. Resistance r (usually 1-2 Ohm) must be much less than the inductor’s resistance, so that the parameters of the circuit would change less when the inductor is taken off. The power dissipated by this resistor should not exceed the limit.

The method for determining the amplitude of the studied waveform depends on its shape. For sinusoidal waveform, as a rule, any electronic voltmeter is suitable, but it is necessary to get acquainted with its description in order to find out in which values the scale is graduated. Usually, MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

these are effective values with scales are set out in average or straightly in amplitude values. The necessary recalculation is easy to be made in accordance with the formula (1):

U am  1,414U e  1,571U av .

When the waveform is non-sinusoidal, for example, pulsed or impulsive, it is not easy to find a suitable voltmeter for its metering, so an oscillograph is used. First of all, vertical extension is fixed, wherein the maximal range of the studied signal is within working part of the screen. In this position the responsiveness of oscillograph in vertical direction is determined with the use of an acquainted external sinusoidal

q  2,8U ra / hr , mV/line where đ?‘ˆđ?‘&#x;đ?‘Ž – effective value of sinusoidal voltage defined with voltmeter, mV; â„Žđ?‘&#x; – the range of sinusoid image according to oscillograph screen scale or using internal calibrator.

Then, leaving unchanged vertical extension of the oscillograph, the studies signal is applied onto vertical plates, and its range h is determined within indications on the screen. Then, if the irregular signal is monopolar, amplitude value of its current is Uam=q¡h, mĐ’, and if the signal is symmetrically bipolar, so Uam=q¡h/2ПВ, and if the coefficient of pulsation is being determined, then: k p  gh / I av r ďƒ— 100 , %,

where I av – power in inductor circuit metered by magnetoelectric device, mĐ?, and r, Ohm. Summary. In magnetic therapy and magneto biology magnetic fields are characterized by a large variety of options for measurement, which are used for measuring the parameters of the magnetic field. The choice of instrument for measuring parameters of magnetic field depends on the current form that feeds the inductor and method of measurement of parameters of the magnetic field.

The intensity of the variable magnetic field is characterized by amplitude values of magnetic induction and its gradient. Because of research established ties of amplitude, average and current values of the sine wave, pulsating double-wave and half-wave curves. Found that as the relevant period changes to duration of half-wave the average and current values.

Substantiation of the features of the application of instruments for measuring magnetic induction direct current and sinusoidal magnetic fields. Inductive measurement technique of the variable magnetic induction confirmed their effectiveness in measuring sinusoidal and non-sinusoidal magnetic fields using electronic an oscilloscope to determine the law of change of the non-sinusoidal magnetic field.

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papers. P. 21-24.

[3] V. Stasyuk (2014). Basics of creating money measuring the magnetic field of the Earth. Existing solutions. Scientific proceeding of Ukrainian research institute of communication, â„–1, P. 87-92.

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