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The evaluation measuring of the variable magnetic fields is in an environment
The problems of measuring of the magnetic and variable electromagnetic fields many works /are sacred to 1-4/. Analysing literature it is possible to say that most often for measuring of the magnetic fields use methods, based on the phenomenon of electromagnetic induction and effect of Hall.
The induction method of measuring is based on the phenomenon of electromagnetic induction, consisting in that in a conducting contour, placed in the magnetic field, at certain terms there is electromotive force (E.M.F.) which is determined by the known expression :
(1)
where N is an amount of coils in a contour, Ф is a magnetic stream, piercing a contour, t is time.
An induction method can be used for measuring of sizes and variable and permanent magnetic fields.
For measuring of the permanent magnetic fields it is necessary in time to change one or a few parameters directly induction-coil (contour) : corner α between a normal to the plane of contour and vector of magnetic induction, area of contour of S, relative permeance of mandrel μc, coefficient of demagnetization of mandrel of k. Size E.M.F. induction for these terms can determine expression
(2)
where is the so-called generalized parameter of induction-coil,
the details of which for hired are not important.
Exactness of measuring of the magnetic fields by means of induction sensor depends both on the structural features of sensor and in large part from the chart of measuring and secondary apparatus qualificatory the size of output signal.
Here it should be noted that an in practice measureable signal, as a rule, does not have a regular sinewave shape, often as separate impulses et cetera
Essence of measuring method by means of transducers (sensors) of Hall consists of the use of effect of Hall, consisting in an origin E.M.F. in direction perpendicular current of I in the plate of explorer, placed in the magnetic field of В. At the permanent size of current in a plate, value E.M.F. determined by expression
, (3)
where And is a constant, changing within the limits of 1.2 depending on the mechanisms of dispersion of transmitters of current, n is a concentration of transmitters of current in material of plate, e is a charge of електрона, d is a thickness of plate.
For making of transducers of Hall apply semiconductor materials, because in them the examined effect has a most value. Thus semiconductors are lately used as tapes on insulating bases, that simplifies technology of making, enables miniature et cetera
A most sensitiveness is possessed by the transducers of Hall on the basis of InSb, GaAs. In addition, for the increase of sensitiveness use different technological receptions: integral execution, use of ferromagnetic concentrators and other 1,2,4/.
By us experimental estimation of sizes of the variable magnetic fields in an environment, arising up during work of different domestic and industrial technique conducted by means of the induction-coil made by us and on occasion by the transformer of Hall on the basis of InSb.
Measuring by means of induction-coil was conducted after her calibrating on the simplified chart of connecting. At calibrating a spool took place in the variable magnetic field, created by the sinewave current of I in an explorer. An alternator was used for this purpose. An output signal from a spool was measured by means of voltmeter of variable tension.
The size of magnetic-field on certain distance of r from an explorer settled accounts on the basis of law of Bio-Savara-Laplasa
, (4)
where μ is relative permeance of environment, μo = 4π·10^-7 Гн/of m - magnetic permanent.
Distance from an explorer, size of current and frequency of him changed at calibrating. Then results were усреднены and a chart is made.
On a fig. 1 dependence of nascent electromotive force is shown in a spool (measureable a voltmeter tension) from frequency of variable magnetic-field (current in an explorer).
Fig. 1. Dependence of sensitiveness of k =ΔU/ΔB the made induction-coil from frequency of magnetic-field of f
At subsequent practical application of spool an output signal and his frequency was measured. For realization of calibrating and practical measuring a the same voltmeter was used, because his technical descriptions can influence on the got results. From got data and calibrating plot the size of variable magnetic-field was determined.
At measuring by means of transformer of Hall on the basis of InSb a ferromagnetic concentrator was used. As a result a sensitiveness made approximately 1·104 мВ/Т and can be megascopic at the improvement of construction. Given, got by means of transducers of Hall, within 20% coincided with the results of measuring an induction-coil.
Certain by us sizes over of the variable magnetic fields, radiated by different electrical engineerings devices, are brought in a table:
Table. Results of measuring of the fields of different sources
Existent sanitary norms on the possible levels of the magnetic fields, taken from different sources, make the sizes of 0.2-0.5 mkТ. It is here possible to mark that frequencies over of radiation are not brought in the literature known to us, although from the physical point of view they not identically can influence on biological objects.
In spite of the simplified enough approach, the got results not badly comport with the known literary data, resulted, for example in /2/. It allows to talk about possibility of application of the described methods for an indication and estimation of levels of electromagnetic radiations, creation of inexpensive (domestic) indicators of electromagnetic radiation, and also creation of high-fidelity measuring devices on the basis of transducers of Hall.
Literature
1. V. V. Panin, B.М.Stepanov. Measuring of the impulsive magnetic and electric fields. - М.: Energoatomizdat, 1987. - 120 p.
2. І.А. Bolshakova, М. Gladun, L. Cupboard that al. Microelectronics of the sensors device magnetic field : Monograph / After by a release Z.Yu. Gotru. - Lvov: Publishing house of the National university "Lviv politekhnika", 2001. - 412 p.
3. I.M.Vikulin, V. I.Stafeev. Physics of semiconductor devices. - М.: Radio and connection, 1990.- 264 p.
4. О. К.Homeryki. Semiconductor transducers of magnetic-field. - М.: Energoatomizdat. 1986. - 136p.
N.Т. Gorbachuk, P. I. Didenko. Materials of conference are "Scientific researches and their practical application. Modern state and ways of development '2010"". Collection of scientific labours, Odesa, 2010
See also:
CONVERTERS, GAUGES, SENSORS
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