RU2071097C1 - Process for measuring magnetic field by quantum magnetometer - Google Patents

Abstract

FIELD: measurement of magnetic induction. SUBSTANCE: measurements of magnetic induction are conducted in number of point of measured fields range and values of systematic error are compared as function of measured field $$$ which is approximated by sections of straight lines so that approximating straight lines are away from function by not greater than specified systematic error. Values of magnetic induction $$$ in crossing points of straight lines and values of systematic error $$$ corresponding to them are entered into storage. In each cycle subrange where measured value of induction B is lying is found so that $$$. Values $$$ corresponding to points of crossing of approximating straight lines nearest to measured value are extracted from storage and corrected value $$$ is computed by formula $$$. EFFECT: increased reliability of measurements. 2 dwg

Description

 The invention relates to the field of magnetic measurements using quantum magnetometers and can be used for absolute measurements of the geomagnetic field in ground, aerial and other magnetic surveys.

 Known quantum magnetometers based on the Zeeman effect in vapors of alkali metals and inert gases using the principle of optical pumping (for example, pedestrian magnetometers MM-ZZ, MM-ZZM, MMP-304, MM-60 and KAM-28 aeromagnetometers, which are commercially available for geophysical measurements , MM-305) (Handbook of the operator-magnetic prospector / Edited by V.E. Nikitsky. M. Nedra, 1987, p. 176), in which the procession frequency is converted into a digital magnetic induction code. Of all magnetometers used in geophysics, quantum ones have the highest sensitivity (up to 0.01 nT), which determines their widespread use in prospecting and exploration of minerals.

 A common drawback of quantum magnetometers is the relatively large systematic error (from 20 to 40 nT). The main sources of this error are the nonlinear dependence of the frequency of the procession on the external field and the phase-frequency characteristic of the measuring-conversion path, which is unstable for various devices of even one series. This circumstance limits the application of quantum magnetometers to the field of field increment measurements (ΔT magnetometers).

 The method of measuring magnetic induction used in the MM-305 aeromagnetometer (ed. St. N 600727 Signal frequency to digital code converter) is adopted as a prototype.

 The specified method does not allow the use of quantum magnetometers for absolute measurements. In addition, the construction of, for example, differential magnetometers and gradiometers based on quantum sensors does not allow anomalies to be judged quickly (on board carriers) during the survey due to various systematic errors depending on the values of the measured induction.

 The objective of the invention is the provision of the possibility of using quantum magnetometers as an absolute measuring tool. This will increase the accuracy and sensitivity of absolute measurements of the magnetic field. In addition, a decrease in the systematic error to the level of units or fractions of a nanotesla will make it possible to create gradiometric systems with the possibility of estimating real anomalies during the survey.

The problem is solved as follows. In the measure of magnetic induction, measurements are made by quantum and exemplary (absolute) magnetometers at a number of points in the range of the measured fields. The values of the systematic error are calculated as a function of the measured field: ΔB = f (B _x ). The obtained function is approximated by line segments so that the distance of the approximating lines from the curve ΔB = f (B _x ) along the ordinate axis does not exceed a predetermined systematic error: the values of magnetic induction B _n are recorded in the memory of the computing device at the intersection points of the approximating lines and the corresponding values of the systematic error ΔB _n .. The number of approximating straight lines and, accordingly, the number of subranges can be different and depend on the form of the function ΔB and the value of the given systematic error, to which determine the degree of approximation of the function by linear sections.

In the measurement process, in each cycle, determine the subrange in which the measured value of the induction B _x lies so that B _n-1 ≅ B _x <B _n . The values corresponding to the intersection points of the approximating lines closest to the measured value are retrieved from the memory.

.The corrected magnetic induction value is calculated.

.

где B_n-1 и B_n значения индукции, соответствующие границам поддиапазона, в который попадает измеренное значение индукции.

where B _n-1 and B _n are the induction values corresponding to the boundaries of the subrange into which the measured induction value falls.

ΔB _n-1 and ΔB _{n are the} values of the systematic errors of the quantum magnetometer corresponding to the boundaries of the subband.

 Thus, the corrected value of magnetic induction turns out to be arbitrarily close to absolute at any point in the measurement range, and a quantum magnetometer can be used to perform absolute measurements with high accuracy in real time.

 In FIG. Figure 1 shows the dependence of the systematic error on the measured field and approximating line segments approximating the proposed method for measuring the magnetic field.

 In FIG. Figure 2 shows the same dependences in the range from 20 to 100 μT, constructed from the results of measurements with the MM-60 pedestrian quantum magnetometer and the MDL absolute exemplary magnetometer in the measure of magnetic induction of the first discharge.

To implement the method, it is necessary to perform the following operations:
1) Convert the procession frequency of the quantum sensor into a digital magnetic induction code.

 2) To measure magnetic induction, take measurements with quantum and exemplary (absolute) magnetometers.

 3) Calculate the values of the systematic error as a function of the measured field.

 4) To approximate the obtained function by line segments depending on a given systematic error.

5) Remember the values of the magnetic induction B _n at the intersection points of the approximating straight lines and the corresponding values of the systematic error ΔB _n ..

6) In each measurement cycle, determine the subrange in which the measured induction value B _x lies so that B _n-1 ≅ B _x <B _n .

7) Retrieve from the memory the values corresponding to the intersection points of the approximating straight lines B _n-1 , B _n , ΔB _n-1 , ΔB _n ..

по формуле:

Кривая зависимости систематической погрешности от измеряемой величины, представленная на фиг. 1, исходя из заданной величины погрешности, аппроксимирована пятью прямыми 1 5, пересекающимися в точках

. При этом весь диапазон оказывается разбит на 5 неравных поддиапазонов. Точки на оси абсцисс B₁ и В₆ являются границами диапазона измеряемых полей соответственно 20 и 100 тыс. нТл. Значения координат указанных шести точек запоминают. Пусть, например, измеренное значение магнитной индукции соответствует 75 тыс. нТл. Определяют, что значение лежит в пределах В₄ 75000 В₅. Извлекают из памяти значения B₄, B₅, ΔB₄, ΔB₅ и вычисляют исправленное значение

по формуле:

На фиг. 2 представлена реальная кривая ΔB=f(B_x) для переходного квантового магнитометра ММ-60. Величина систематической погрешности в диапазоне измеряемых полей составила от 1,2 до 11,5 нТл. Кривая В f(B_x) аппроксимирована тремя прямыми, исходя из заданной систематической погрешности ΔB_макс ≅ 0,5 нТл.. На фиг. 2 это величина отстояния кривой от аппроксимирующей прямой по оси ординат в точке 80 тыс. нТл. Для данного образца необходимо запомнить значения погрешности в точках пересечения аппроксимирующих прямых (20000: 1), (56000:2,7), (91000:8,6), (100000:11,5). Так, для измеренного магнитометром ММ-60 значения магнитной индукции 75000 нТл, исправленное значение будет равно:

что совпадает с контрольным измерением абсолютным магнитометром нТл с точностью 0,3 нТл.8) Calculate the corrected induction value

according to the formula:

The curve of systematic error as a function of the measured quantity shown in FIG. 1, based on a given error value, is approximated by five straight lines 1 5, intersecting at points

. In this case, the entire range is divided into 5 unequal subbands. The points on the abscissa axis B ₁ and B ₆ are the boundaries of the range of measured fields, respectively, 20 and 100 thousand nT. The coordinate values of these six points are stored. Let, for example, the measured value of magnetic induction correspond to 75 thousand nT. Determine that the value lies within the range of B ₄ 75,000 B ₅ . The values B ₄ , B ₅ , ΔB ₄ , ΔB ₅ are retrieved from the memory and the corrected value is calculated

according to the formula:

In FIG. Figure 2 shows the real curve ΔB = f (B _x ) for the transition quantum magnetometer MM-60. The value of the systematic error in the range of measured fields ranged from 1.2 to 11.5 nT. Curve B f (B _x ) is approximated by three straight lines, based on a given systematic error ΔB _max ≅ 0.5 nT. In FIG. 2 is the value of the distance of the curve from the approximating line along the ordinate axis at the point of 80 thousand nT. For this sample, it is necessary to remember the error values at the intersection points of the approximating straight lines (20000: 1), (56000: 2.7), (91000: 8.6), (100000: 11.5). So, for the value of the magnetic induction measured by the MM-60 magnetometer 75000 nT, the corrected value will be equal to:

which coincides with the control measurement with an absolute nTl magnetometer with an accuracy of 0.3 nT.

 Thus, the proposed method allows to increase the accuracy of the measurements of a quantum magnetometer and use it as an absolute magnetometer.

Claims (1)

A method of measuring a magnetic field with a quantum magnetometer, based on the conversion of the procession frequency to a digital code, characterized in that the measurements are made with magnetic and quantum (absolute) magnetometers in the range of the measured fields with magnetic induction, and the values of the difference in their readings are calculated as a function of the measured field ΔB = f (B _x), which is approximated by straight line segments so that the lag of the curve approximating straight ΔB = f (B _x) on the y axis does not exceed the predetermined systematic error values are stored agnitnoy induction at the points of intersection approximating straight lines B _n and the corresponding difference between the readings and exemplary quantum magnetometers, each measurement cycle is determined subband in which lies the measured induction value _x such that B _{n - 1} ≅B _x <B _n, recovered from memory values corresponding to the points of intersection of the approximating straight lines B _{n - 1} , B _n , ΔB _n-1 , ΔB _n closest to the measured value and the corrected magnetic induction value B _{x isp.} according to the formula

where B _{n - 1} and B _{n are the} values of induction corresponding to the boundaries of the subrange into which the measured value of induction falls;
ΔB _n-1 and ΔB _{n are the} values of the difference between the readings of the quantum and reference magnetometers corresponding to the boundaries of the subband.

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