WO2012054000A1

WO2012054000A1 - Method for measuring magnetic field

Info

Publication number: WO2012054000A1
Application number: PCT/UA2010/000090
Authority: WO
Inventors: Inessa A. Bolshakova; Roman L. Holyaka
Original assignee: Bolshakova Inessa A; Holyaka Roman L
Priority date: 2010-10-21
Filing date: 2010-11-30
Publication date: 2012-04-26
Also published as: EP2630511A4; EP2630511A1; UA99187C2

Abstract

The method for measuring magnetic field includes measuring the output voltage of the galvanomagnetic transducer and calculation induction of the measured magnetic field according to the measured values of the output voltage and sensitivity of the galvanomagnetic transducer; herewith, the galvanomagnetic transducer contains, at least, two pairs of leads, and measurements are carried out in two stages - at the first stage the first pair of leads is used to supply power to the galvanomagnetic transducer, while the other pair is used to measure the output voltage; at the second stage the first pair of leads is used to measure the output voltage, whereas the other pair is used to supply power to the galvanomagnetic transducer. Sensitivity of the galvanomagnetic transducer is found, at least at one of the above stages by measuring at least two values of the output voltage, the first of which is caused by the action of measured magnetic field only, and the second is caused by the sum of the measured magnetic field and the test field, whose magnitude is given in advance.

Description

METHOD FOR MEASURING MAGNETIC FIELD

The invention relates to measurement instrumentation, namely to the methods for measuring the magnetic field based on galvanomagnetic measuring transducers, and can be used for measuring, in particular, the quasi-stationary magnetic fields in thermonuclear fusion reactors.

A magnetic field measurement method based on the measuring of the output voltage of the galvanomagnetic transducer, in particular, of the semiconductor Hall transducer, and, further calculation of magnetic field induction using previously given value of transducer sensitivity is known, [Popovic R.S. Hall effect devices: magnetic sensor and characterization of semiconductors. IOP Publishing Ltd. 1991. P. 188. Fig. 4.22.]. By applying voltage (current) supply to galvanomagnetic transducer in the respective way, charge carrier flow is being formed.

Under the action of Lorentz force on moving charge carriers a signal is being generated in the galvanomagnetic transducer, for example, voltage difference on Hall transducer output leads. This voltage is an informative signal of magnetic field measurement process. The coefficient of conversion from measured voltage to magnetic field induction is known in advance and constant.

The disadvantage of this method is in the low accuracy of magnetic field measurement under extreme operation conditions, in particular, under high penetrating radiation. The reason for this is a change of electrical and physical parameters of galvanomagnetic transducers under penetrating radiation; particularly, the change of sensitivity (conversion transconductance , that is a multiplicative component of conversion linear function) and residual voltage (output voltage under zero value of magnetic field, that is an additive component of conversion linear function) of galvanomagnetic transducers under the long term action of charged particles or neutrons. A magnetic field measurement method based on the galvanomagnetic transducer output voltage measurement and calculation of induction of magnetic field being measured applying the above voltage value and the sensitivity (multiplicative component of conversion linear function) of the aforesaid transducer; herewith, the transducer sensitivity is determined in the process of its periodical calibration with the use of test magnetic field. This calibration is performed in-situ, i.e. directly inside the object, where a measuring probe is placed for taking magnetic field measurement. Test magnetic field is provided with the coil, inside which a galvanomagnetic transducer is placed. The abovementioned coil and the galvanomagnetic transducer properly placed in it form a unified structure, which is a functionally integrated probe. Test magnetic field magnitude, which is provided by the coil current supply and is considered to be known, and the measured galvanomagnetic transducer output voltage value, determined by the test magnetic field, are the informative values for galvanomagnetic transducer sensitivity calculation. [Bolshakova I., Holyaka R., Leroy C. Novel approaches towards the development of Hall sensor-based magnetometric devices for charged particle accelerators // IEEE Transactions on Applied Superconductivity. - 2002. Vol.12, N'l. - P. 1655-1658.]. The advantage of the above mentioned measurement method

[Bolshakova I., Holyaka R., Leroy C. Novel approaches towards the development of Hall sensor-based magnetometric devices for charged particle accelerators // IEEE Transactions on Applied Superconductivity. - 2002. - Vol.12, ΝΊ . - P. 1655-1658.] is a possibility of periodical calibration by determining the sensitivity (multiplicative component of conversion linear function) , of galvanomagnetic transducer under the long term action of penetrating radiation. It is fundamentally important that in the process of periodical calibration there is no need to take the probe out of the object, where magnetic field is measured. This advantage is of fundamental importance in magnetic field measurements under radiation operation conditions, particularly, in reactors or charged particle accelerators . A drift of galvanomagnetic transducer parameters occurs under high radiation conditions, therefore, they need periodical calibration. This calibration shall be performed in-situ.

The disadvantage of the above mentioned method [Bolshakova I., Holyaka R., Leroy C. Novel approaches towards the development of Hall sensor-based magnetometric devices for charged particle accelerators // IEEE Transactions on Applied Superconductivity. - 2002. - Vol.12, ΝΊ . - P. 1655-1658.] is low accuracy of periodical in-situ calibration, caused by the impossibility to determine the drift, under radiation operation conditions, of residual voltage (additive component of conversion linear function) .

The method of compensating the Hall galvanomagnetic transducer residual voltage, containing two pairs of leads is known. In this case measurements are carried out in two stages [Popovic R.S. Hall effect devices: magnetic sensor and characterization of semiconductors. IOP Publishing Ltd. 1991. P. 190. Fig. 4.24.]. At the first stage the first pair of leads is used to supply power to the galvanomagnetic transducer, while the other pair is used for measuring the output voltage; at the second stage, the first pair of leads is used for measuring the output voltage, whereas the other pair is used to supply power to the galvanomagnetic transducer. The values of output voltages of the first and second stages of measuring are summed up, which enables to compensate the residual voltage of the galvanomagnetic transducer with no need to perform periodical determinations of drift of this residual voltage (additive component of conversion linear function) by shifting the galvanomagnetic transducer from the area of magnetic field measurements to the zero-chamber (device, which by magnetic shielding provides zero value of magnetic field) .

The advantage of the above method of measurement [Popovic R.S. Hall effect devices: magnetic sensor and characterization of semiconductors. IOP Publishing Ltd. 1991. P. 190. Fig. 4.24.] is in compensating the impact of drift of residual voltage (additive component of conversion linear function) in radiation operation conditions of galvanomagnetic transducer on the result of the magnetic field measuring.

The disadvantage of the aforesaid method of measurement [Popovic R.S. Hall effect devices: magnetic sensor and characterization of semiconductors. IOP Publishing Ltd. 1991. P. 190. Fig. 4.24.] is the impossibility to determine the sensitivity drift (multiplicative component of conversion linear function) of the galvanomagnetic transducer, which decreases the accuracy of the magnetic field measurements.

The invention is based on the objective to improve the accuracy of the already known method for magnetic field measuring with the use of the galvanomagnetic transducer which contains, at least, two pairs of leads; in this case the measurements are carried out in two stages - at the first stage the first pair of leads is used to supply power to the galvanomagnetic transducer, while the other pair is used to measure the output voltage; at the second stage, the first pair of leads is used to measure the output voltage, and the other pair is used to supply power to the galvanomagnetic transducer. Herewith, the accuracy is improved due to periodical calibration of the galvanomagnetic transducer while measuring the magnetic field using for this calibration at least two values of output voltage, the first being provided by the action of the measured magnetic field only, whereas the other represents the sum of the measured magnetic field and test field, whose value is given in advance. The suggested method for measuring magnetic field is further grounded on the following figures.

Fig. la and Fig. lb show the schemes of forming the output voltage of the galvanomagnetic transducer, caused by the measured B_x magnetic field at the first stage (Fig. la) and at the second stage (Fig. lb) .

Fig. 2a and Fig. 2b demonstrate the schemes of forming the output voltage of the galvanomagnetic transducer, caused by the sum of the measured B_x and test B_R magnetic fields at the first stage (Fig. 2a) and at the second stage (Fig. 2b). The galvanomagnetic transducer (Hall Generator, HG) is a standard rectangular semiconductor structure that has two pairs of leads: the first pair - leads la, lb, the other pair - leads 2a, 2b. These transducers operate on the principle of charge carrier deflection under the action of Lorentz force, and the discrepancy between their output voltages is caused by the Hall effect.

The power supply to the HG transducer is through a voltage or current source (E) . While supplying power to the HG transducer via leads la, lb, output voltage VIOUT is released from leads 2a, 2b ( Fig . la) . the equivalent scheme of the galvanomagnetic transducer is represented by resistors R₀ and R_z, whereas resistance R_z is included into the equivalent scheme for describing nonsymmetric nature of the transducer. The structure of the ideal galvanomagnetic transducer is symmetric, which meets the condition of R_z = 0 . in case of the lack of magnetic field ( B=0 ) the output voltage of the ideal HG transducer is zero V₀UT ( B=0 ) = 0 .

However, the existing transducers do not have the ideal symmetry, which is caused, in particular, by the uneven distribution of admixtures in the semiconductor material from which the transducer was made, deviation in the structure size, anisotropy etc. The availability of resistance R_z, which represents the total influence of the above effects on the output voltage, leads to formation of the residual voltage V_0UT ( B=0 ) = V_RZ .

Under the action of magnetic field B_X the output voltage VIOU of the galvanomagnetic transducer ( Fig . la) is approximately proportional to the magnetic field induction B_X and under the availability of the residual voltage V_RZ it equals

Where _B - sensitivity (proportion coefficient of conversion linear function) . As it is seen from the scheme in Fig. lb, at the second stage of measuring the sign of the residual voltage V_RZ becomes opposite, that is the output voltage of the galvanomagnetic transducer is

¼_OUT ⁼ -_Β-Ε^_Χ ^— V_RZ . ( 2 )

The effect of the residual voltage V_RZ compensation is achieved by summing up the results of measurements of both stages

Thus, the V_RZ residual voltage drift of the galvanomagnetic transducer, which occurs, in particular, under long term radiation operation conditions of the transducer, does not affect the result of the above two-stage measurement. Nevertheless, the sensitivity drift K_B is still a problem, which does not enable to achieve the required accuracy of magnetic field measuring.

This problem, complying with the invention, may be eliminated by the fact that sensitivity K_B of the galvanomagnetic transducer is found at least during one of the above stages by determining minimum two values of output voltage, the first of which is caused by the measured magnetic field, while the other is caused by the sum of the measured magnetic field and test field, whose value is given in advance (Fig.2a, Fig.2b) .

The result of measuring the output voltage, caused by the sum of the measured B_x and test B_R magnetic fields while using the galvanomagnetic transducer according to scheme of the first stage is

V₃₀uT=K_B(B_X+B_R)+V_RZ. (4)

Similarly, the output voltage under the scheme of the second stage is

^V40UT ^{= K}B(^BX ^{+ B}R)^{_ V}RZ ^■ (5)

Using the results of the carried out measurements, it is possible receive the following:

¼OUT ^— ^IOUT ⁼ ^B^BR ( 6 )

The sensitivity of the galvanomagnetic transducer is found by using equation (6) or (7)

V -V

K_B = ^{30UT 10UT} (8)

The measurements of the output voltage of the galvanomagnetic transducer, caused by the sum of the measured B_x and test B_R magnetic fields, may be made by using a coil, which, together with the galvanomagnetic transducer, creates an integrated measuring probe and is placed in the magnetic field measurement area.

There are two ways of creating a test magnetic field.

Under the first way the value of the beforehand given test magnetic field B_R is achieved by supplying power to the coil at the given current. The magnitude of the magnetic field of the coil is determined by its geometrical dimensions, number of loops and the power supply current. Therefore, this test field does not depend on destabilizing radiation operation conditions and may be considered to be constant and given in advance.

The other way of creating the test magnetic field suggests that the measured field is a variable value. The change of the measured magnetic field is established with the use of the coil and serves as test field B_R. Like in the abovementioned first way, it is possible to ignore the impact of radiation conditions and of the coil parameters; consequently, a signal from the coil, with the use of which the magnitude of the test field B_R is determined, may be considered constant.

It should be noted that the use of the coil for measuring the change of the measured magnetic field, that serves as the test value B_R, is justified only under specific parameters of this field change. Thus, the coil, whose output voltage value is determined by the speed of the magnetic field change with the time, doe not enable to measure stable or quasi- stationary magnetic fields, and therefore, it may not replace the galvanomagnetic transducer in the suggested measurement method. Instead, the galvanomagnetic transducer doe not have any limitations on measuring stable or quasi-stationary magnetic fields, however, the stability of its residual voltage and sensitivity to destabilizing, particularly, radiation operation conditions, are unsatisfactory.

This problem is solved by the offered method for measuring magnetic field, which enables to combine, on the one hand, residual voltage compensation, on the other calibration of the galvanomagnetic transducer sensitivity. Consequently, the suggested method provides high accuracy of measuring magnetic field with the use of the galvanomagnetic transducer under long term destabilizing operation conditions, for instance, under the action of high penetrating radiation.

Depending on operation conditions (level of destabilizing impact) the method under discussion enables to considerably improve the accuracy of measurements. In particular, under the fluence of fast neutrons of 10¹⁸ cm^-2 degradation of the galvanomagnetic transducer based on semiconductor material InSb leads to the increase of residual voltage by 5 times (particularly, for the standard sample of Hall transducer with V_RZ = 1 mV to V_RZ = 5 mV) to decrease of the sensitivity by 7 times (in particular, under K_B = 350 mV/T to K_B = 50 mV/T) . It is evident that tolerance of the measurement made by the magnetic transducer with the use of the above sample of Hall transducer is within 75% - that means that it is possible to consider that measuring as process becomes purposeless. Instead, the use of the suggested method for measuring provides residual voltage compensation to the rate of 0.1 mV and calibration of sensitivity with the tolerance of maximum ±0.25% (under 0.2% nonlinearity of conversion function K_B within the range of magnetic field IT) , which totally corresponds to the tolerance of magnetic field measuring of up to ±0.3% (within the range of magnetic field from ±0.03T to ±1T) .

Claims

1. The method for measuring magnetic field, which includes measuring output voltage of the galvanomagnetic transducer and calculation of induction of the measured magnetic field according to the measured values of the output voltage and sensitivity of the galvanomagnetic transducer; herewith, the galvanomagnetic transducer contains, at least, two pairs of leads, and measurements are carried out in two stages - at the first stage the first pair of leads is used to supply power to the galvanomagnetic transducer, while the other pair is used to measure the output voltage; at the second stage the first pair of leads is used to measure the output voltage, whereas the other pair is used to supply power to the galvanomagnetic transducer, which is characterized in that sensitivity of the galvanomagnetic transducer is found, at least at one of the above stages by measuring at least two values of the output voltage, the first of which is caused by the action of measured magnetic field only, and the second is caused by the sum of the measured magnetic field and the test field, whose magnitude is given in advance.