RU2053521C1 - Magnetic field meter - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: meter has set of similar parallel, equally oriented Hall-effect transducers separately supplied with control current and connected in series for Hall-effect emf. Centers of transducers are located on common neutral to their planes. Total height "c" of set depends on transducer width "b" and equals

in case of two transducers;

Description

 The invention relates to magnetic measurements in various electrophysical equipment, creating a flat inhomogeneous magnetic field, mainly in magnetic systems of charged particle accelerators and wiring systems of external beams of these particles.

 Known miniature Hall sensors suitable for measuring any inhomogeneous fields (in particular, and flat).

 A disadvantage of the known sensors is the low sensitivity to the magnetic field associated with the small width of the sensor.

 A known probe for measuring magnetic induction, consisting of Hall sensors and adopted as a prototype.

 The disadvantage of this probe is that it is not suitable for measuring non-uniform fields, when field inhomogeneity significantly affects the size of the sensor. When using miniature sensors, it is possible to measure the inhomogeneous field, however, the sensitivity of the probe is sharply reduced.

 The purpose of the invention is to ensure the measurement accuracy of a planar inhomogeneous magnetic field while increasing the sensitivity of the meter.

в случае двух датчиков; c b

в случае нечетного числа (2N+1) датчиков, где N=1; 2; 3 а датчики равномерно распределены по высоте набора с.The goal is achieved in that in a meter containing the same Hall sensors, according to the invention, the latter are parallel to each other and are equally oriented, their centers are on the common normal to the planes of the sensors, provided with separate power supply for the control current and connected in series along the Hall emf, and the common the height from a set of sensors depends on their width b and is equal to c

in case of two sensors; cb

in the case of an odd number (2N + 1) of sensors, where N = 1; 2; 3 a, the sensors are evenly distributed over the height of the set s.

при двух датчиках, c b

при нечетном числе (2N+1) датчиков) применять не миниатюрные, а обычные датчики Холла. При отклонении от указанных геометрических соотношений в конструкции измерителя последний будет давать погрешность в величине измеряемого поля, поскольку начнет реагировать не только на поле в центре датчика, но и на пространственные производные поля.Separate power supply for the control current is necessary so that the current does not branch, distorting the sensor signals, into the measuring circuit where the Hall signal emfs are connected in series, which allows you to measure the field in the center of the meter based on the sum of the signal emfs of the individual sensors and with great sensitivity, since in the meter it is possible with the proper ratios between geometric parameters (c

with two sensors, cb

with an odd number (2N + 1) of sensors) use not miniature, but conventional Hall sensors. If you deviate from the indicated geometric relationships in the meter design, the latter will give an error in the magnitude of the measured field, since it will begin to respond not only to the field in the center of the sensor, but also to the spatial derivatives of the field.

 In FIG. 1 shows the active plate of the Hall sensor; in FIG. 2-5, it is shown how, when measuring a flat field, it is necessary to arrange, in relation to the latter, various versions of the meters, as well as a separate Hall plate (Fig. 2).

в случае двух датчиков; c b

в случае нечетного числа (2N+1) датчиков, где N=1; 2; 3 а датчики равномерно распределены по высоте набора с.The meter contains a set of identical Hall sensors parallel to each other, the centers of which are located on a common normal to the planes of the sensors, provided with separate power supply for the control current and connected in series along the Hall emf. The total height from a set of sensors depends on the width b and is equal to c

in case of two sensors; cb

in the case of an odd number (2N + 1) of sensors, where N = 1; 2; 3 a, the sensors are evenly distributed over the height of the set s.

постоянно. При использовании одной отдельной пластины Холла (фиг. 2) нужно ее центp совместить с точкой измерения и направить ось β по нормали к плоскостям, в которых лежат силовые линии. Вращая датчик вокруг оси β, ориентируют ось γ в направлении измеряемой компоненты поля.The active plate of the Hall sensor is shown separately in FIG. 1, where its coordinate system α, β, γ is introduced and the geometric parameters are indicated. The control current i _{1 is} passed along the axis β, and the signal emf U is removed from points 1 and 2. In FIG. 2-5 show how to position a separate Hall plate for measuring a plane inhomogeneous field (Fig. 2), or shown in Figs. 3-5 suggested meters. It is believed that the field lines of force lie either in the plane of the drawing or in other planes parallel to it and that on any normal to these planes the field

constantly. When using one separate Hall plate (Fig. 2), it is necessary to align its center with the measurement point and direct the β axis along the normal to the planes in which the lines of force lie. Rotating the sensor around the β axis, the γ axis is oriented in the direction of the measured field component.

 Each meter (Fig. 3-5) is associated with a coordinate system x, y, z, having a beginning in the center of the device. The z axis coincides with the γ axes of the sensors included in the meter, and the y axis is parallel to the β axes of the same sensors. When measuring, you need to combine the origin of the x, y, z system of the meter with the measuring point and direct the y axis along the normal to the planes in which the lines of force lie (i.e., to the drawing plane in Figs. 3-5). Rotating the meter around the y axis, orient the z axis along the measured field component. For consistency, the system x, y, z is also introduced in FIG. 2.

B_z(x,z)dx, (1) где К чувствительность пластины Холла в равномерном поле.In all the examples discussed below, it is not necessary to introduce a correction in the signal emf due to the existence of a planar effect. The correction is zero, because (as can be seen from Fig. 2-5) the angle between the control current of any Hall plate and the component of the measured field lying in the plane of the same plate is 90 ^about . Therefore, for the sensor in FIG. 2, you can write the signal emf as
U

B _z (x, z) dx, (1) where K is the sensitivity of the Hall plate in a uniform field.

=

, которое имеет физический смысл средней компоненты B_z на участке от X₁= -b/2 до X₂=b/2. Однако, в общем случае, искомое поле B_z(0,0) отличается от этого среднего значения, и как раз в этом состоит недостаток аналогов, построенных на базе одной отдельной пластины Холла. Добиться точечности измерения, применяя одну холловскую пластину, можно только в случае "миниатюрной пластины", если в пределах ее габаритов можно считать магнитное поле практически равномерным. Однако чувствительность датчика при этом будет малой.From (1), according to the signal U, we can calculate the field

=

, which has the physical meaning of the average component B _z in the region from X ₁ = -b / 2 to X ₂ = b / 2. However, in the general case, the desired field B _z (0,0) differs from this average value, and this is precisely the disadvantage of analogues built on the basis of one separate Hall plate. It is possible to achieve a measurement accuracy using one Hall plate only in the case of a “miniature plate”, if within the limits of its dimensions the magnetic field can be considered almost uniform. However, the sensitivity of the sensor will be low.

In the proposed meters (Fig. 2-5), the active plates included in them are interconnected electrically in series and according to the Hall emf, for which a separate power supply is applied according to the control current i ₁ . As a result, the overall sensitivity to the magnetic field of any device in these figures is so many times greater than that of a single plate, which is equal to the number of plates used. As for the point of reference of the non-uniform field, it is achieved by the proper relative positioning of individual Hall plates (not necessarily "miniature") included in the meter.

To construct the theory of the proposed meter, we represent the field component B _z (x, z) in the vicinity of the coordinate system x, y, z in the form of a power series.

h_m,nx^mzⁿ, (2) где член нулевого порядка h_0,0 равен искомому полю B_z(0,0) в точке измерения. Ввиду равенства нулю лапласиана проекции магнитного поля коэффициенты h связаны соотношением
(m+2)(m+1)h_m+2,n+(n+2)(n+1)h_m,n+2=0 (3)
Поскольку из практики известно, что в разложении поля (2) члены 4 порядка и выше играют незначительную роль, будем принимать во внимание лишь члены не выше 3 порядка.B _z (x, z) =

h _{m, n} x ^m z ⁿ , (2) where the zero-order term h _0,0 is equal to the desired field B _z (0,0) at the measurement point. Since the Laplacian of the magnetic field projection is equal to zero, the coefficients h are related by
(m + 2) (m + 1) h _{m + 2, n} + (n + 2) (n + 1) h _{m, n + 2} = 0 (3)
Since it is known from practice that terms of order 4 and higher play an insignificant role in the expansion of field (2), we will take into account only terms no higher than 3 orders.

The control current i ₁ will be considered uniformly distributed over the b · t section of the Hall plates, which is acceptable in the case of, for example, materials such as I _n S _b n-type, or I _n A _s n-type, in which the ohmic resistance depends little from the magnetic field. The sensitivity k of the individual sensors that make up any meter are equalized by fine tuning the corresponding control currents.

(h_2,0x²+h_0,2z²)dx (4)
Учитывая, что Z²=

и что, как это следует из (3), h_0,2=-h_2,0, получим
U 2KB_z(O,O)+2Kh

(5)
Из (5) видно, что чувствительность измерителя (фиг. 3) к квадратичным членам разложения поля может подавить, если в его конструкции предусмотреть соотношение
c

(6)
В результате получим устройство с чувствительностью k₀=2k и точечным отсчетом поля B_z(0,0)=

(если, конечно, отвлечься от влияния членов разложения поля четвертого и более высших порядков).Consider the theory of a meter consisting of two Hall plates, shown in FIG. 3. When calculating the Hall emfs U ₁ and U _{2 of the} upper and lower plates (respectively), it should be taken into account that the Z coordinates of these plates Z ₁ = c / 2 and Z ₂ = -c / 2 are constant on the surface of each of them. To find the common signal U = U ₁ + U _2, one needs to use formula (1), in which instead of B _z (x, z) substitute the sum (2) in the composition of the terms no higher than 3 orders of magnitude. Moreover, members of an odd order in X are not necessary to substitute, since they give a zero contribution when integrating over X from (-b / 2) to (b / 2). Members of an odd order in Z do not need to be taken into account either, because they (even with an even order in X) will give a zero contribution after the addition operation U ₁ + U ₂ . The result is
UU ₁ + U ₂ = 2KB _z (O, O) +

(h _2.0 x ² + h _0.2 z ² ) dx (4)
Given that Z ² =

and that, as follows from (3), h _0.2 = -h _2.0 , we obtain
U 2KB _z (O, O) + 2Kh

(5)
It can be seen from (5) that the sensitivity of the meter (Fig. 3) to the quadratic terms of the field expansion can be suppressed if the ratio
c

(6)
As a result, we obtain a device with sensitivity k ₀ = 2k and a point reference of the field B _z (0,0) =

(unless, of course, one distracts from the influence of the terms of the expansion of the field of the fourth and more higher orders).

(7)
Остальные пластины, симметрично расположенные относительно плоскости x, y, будем рассматривать парами, присваивая этим парам номера n от 1 до N, по мере удаления соответствующих пластин от центра устройства. Для выражения сигнала U_n от пары с номером n можно воспользоваться готовой формулой (5), в которой вместо фигурирующей там величины с подставить высоту пары c

. Суммируя сигналы всех пар, получим

U_n= 2KNB_z(O,O)+Kh

n

; (8)
Складывая (7) и (8), найдем общий сигнал измерителя
U K(2N+1)B_z(O,O)+Kh

b²

n

(9)
Для подавления чувствительности к члену второго порядка разложения поля (2) здесь нужно выполнить условие
b²

n² (10) что, с учетом формулы для суммы квадратов чисел натурального ряда, приводит к искомому соотношению между геометрическими параметрами датчика
c b

(11)
При соблюдении (11) измеритель (фиг. 5) обладает свойством практически точечного отсчета поля в точке измерения и обеспечивает чувствительность k₀= k(2N+1). В частном случае, когда N=1, получается измеритель из трех активных пластин (фиг. 4). Его чувствительность k₀=3k, а условие (11) выглядит в этом случае, как
c

(12)
Предлагаемое техническое решение, по сравнению с имеющимися, обеспечивает при измерении топографии плоского неоднородного магнитного поля увеличенную (на 1-2 порядка величины) чувствительность аппаратуры, без ухудшения точечности отсчета поля, и расширяет (в сторону малых индукций) диапазон измеряемых плоских неоднородных магнитных полей.The meter (Fig. 5) has a total height c and consists of an odd number (2N + 1) of plates uniformly distributed over the height, the middle of which is at a height of Z = 0. Assigning the number n = 0 to the middle plate, we find its signal U ₀ . For this, it is necessary to use formulas (1) - (3), taking into account in (2) the terms not higher than 3 orders of magnitude. Then we get
U _o = KB _z (O, O) + Kh _2.0

(7)
The remaining plates, symmetrically located relative to the x, y plane, will be considered in pairs, assigning these pairs numbers n from 1 to N, as the corresponding plates move away from the center of the device. To express the signal U _n from the pair with number n, you can use the ready-made formula (5), in which instead of the quantity c appearing there, substitute the height of the pair c

. Summing the signals of all pairs, we obtain

U _n = 2KNB _z (O, O) + Kh

n

; (8)
Adding (7) and (8), we find the total signal of the meter
UK (2N + 1) B _z (O, O) + Kh

b ²

n

(9)
To suppress the sensitivity to the second-order term of the field expansion (2), here it is necessary to fulfill the condition
b ²

n ² (10) which, taking into account the formula for the sum of squares of numbers of the natural series, leads to the desired relationship between the geometric parameters of the sensor
cb

(eleven)
Subject to (11), the meter (Fig. 5) has the property of an almost point reference of the field at the measurement point and provides sensitivity k ₀ = k (2N + 1). In the particular case, when N = 1, a meter of three active plates is obtained (Fig. 4). Its sensitivity is k ₀ = 3k, and condition (11) in this case looks like
c

(12)
The proposed technical solution, in comparison with the existing ones, provides, when measuring the topography of a plane inhomogeneous magnetic field, an increased (by 1-2 orders of magnitude) sensitivity of the equipment, without deterioration of the point accuracy of the field reading, and extends (towards small inductions) the range of measured plane inhomogeneous magnetic fields.

Claims (1)

A MAGNETIC FIELD METER, comprising Hall sensors with separate power supply according to the control current, characterized in that, in order to ensure the accuracy of measuring a plane inhomogeneous magnetic field while increasing the sensitivity to magnetic induction, the sensors are connected in series along the Hall emf, installed in parallel planes and are equally oriented, their centers are located on a common normal to the indicated planes, and the total height C of the set of sensors is

- in the case of two sensors;

- in the case of an odd number of 2N + 1 sensors uniformly distributed over the height of the set C, where b is the width of the sensor;
N = 1, 2, 3, ....

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