DE1623382C - Method and arrangement for compensating self-generated magnetic fields for a magnetometer carried by an aircraft - Google Patents

Description

The invention relates to a ^fe method and an arrangement for compensating for magnetic ^{Eigenstör! In a F] u} g g ^{zeu comprising a} magnetometer for measuring the field strength of an external magnetic field, in particular the terrestrial magnetic field, carrying with it.

For an accurate measurement of the strength of the earth's magnetic field and its changes, it is known a magnetometer, especially one with a magnetic one

To use nuclear magnetic resonance magnetometer installed on board an aircraft

_{! 0} with which the area to be examined is flown over. In general there are numerous electromagnetic devices in aircraft that are not adequately shielded and therefore cause a magnetic interference field (self-interference field), the

, ₅ is superimposed on the field to be measured.

In order to keep the influence of the self-interference field as small _as possible, a move has been made to arrange the actual measuring head of the magnetometer in a probe which is transported outside of the aircraft with the help of a rope. In another case, the measuring head has been arranged in a lance which is attached to the tail end of the aircraft in order to thereby increase the distance from the center of the electromagnetic devices of the aircraft.

To eliminate the inherent magnetic interference fields of an aircraft, it is also known for the To use measuring head two coils and to arrange these coils in such a way that the self-interference fields The electromotive forces caused cancel each other out, while those from the magnetic field to be measured cancel each other out caused signals add up.

There is also an older proposal for a compensation arrangement for a vehicle worn magnetometer, which is used to determine the changes in direction of the vehicle To eliminate falsification of the measurement result. It is assumed here that the influence by the intrinsic interfering field of the vehicle, e.g. an airplane, when measuring the magnetic vision Earth's field generally does not matter when the vehicle is opposite during the measurement the direction of the magnetic field to be measured maintains a fixed direction. To simplify the Measurement is also assumed that the vehicle has an intrinsic magnetic interference field of constant field strength has. But since this is not the case, the influence of the Only partially switch off the self-interference field.

The object of the invention is to provide a

drive and train an arrangement for compensating for the inherent magnetic interference fields of an aircraft in _{such a way} that the interference is caused by a

. i _o n _e walls and automatic compensation for all measurement conditions present fully switched _{OFF w} ill.

_{The gem} AESS _{of the} invention provided for this method is that the difference in field strengths - _the total magnetic field at two points X, Y is determined of the vehicle, where the field strength _{of the} ä _u ß _he s magnetic field is approximately the same, _{however, the} field strengths of the magnetic self-interference field are different, that a current strength proportional to the difference between these field strengths and thus the magnetic self-interference field as a control variable on the

^6s point, at which the measuring head of the magnetometer is located, is generated and that with the help of this control variable a magnetic compensation field is generated which is opposite to the magnetic

Self-interference field is directed and about the same field etc.), which has a constant magnetic compensation strength as the self-interference field. tion require, in an approximately spherical zone R According to the further invention, the arrangement is included, which is in the vicinity of the front end of the to compensate for magnetic interference fields in aircraft, the center of gravity of this zone R an aircraft in such a way that the at - 5 practically coincides with the center of gravity M of the magnetic the points X, Y in the perpendicular plane of symmetry masses of the aircraft. The apparatus of the aircraft on the axis of the same one behind the other in this zone influence a magnetometer head located at X in an area near the aircraft tail, preferably at a distance χ from this center of gravity M at a mutual distance of a few centimeters more than one located at Y in meters and that to generate the io distance χ + dx of the center of gravity M angeord compensation field two in the vicinity of the gravitational magnetometer head. In Fig. 1, Y lies at the point of the magnetic masses of the aircraft tail Q, while X is provided between the tail and arranged coils, the axes of which are located in the zone R , these two positions with the axis of the aircraft forming a triad with three of X and Y Incidentally, form the preferred positions of the right angles. A further embodiment of the arrangement of the entire magnetic field in the inventive method and / or the inventive X, Y a magnetometer head is arranged, which is detected by a device .

first voltage with a frequency 20 proportional to the field strength of the magnet- At X as well as at Y , the total magnetic field field at this point is essentially equal to the sum of two Frequency meter to determine the field strength of the field that would be present at these points, external magnetic field with compensated self-interference - if the aircraft is not provided in the field shown that would be at the other point X position) and the magnetic or Y a magnetometer head with a core filter 25 interference field, which is generated by the aircraft, (bandpass filter) is arranged, which receives at its input and that essentially from the on -board devices arranged within the one part of the first voltage and a zone R , supplies the second voltage, the opposite the first consequently allows a measurement of the total voltage by an angular phase n is shifted, magnetic field at X or Y (or at any of the other point of the aircraft to the difference in field strengths of the entire Ma- 30 other point of the aircraft) by means of a very opposing field at the two points X, Y proportionally accurate magnetometer not, the measurement is the exact one, and that a unit is provided which undertakes the two field strengths of the external magnetic field, receives voltages and a third field is disturbed for the phase, which supplies voltage proportional to the field strength of the magnetic interference displacement angle. The magnetometer measures the total magnetic field proportional to the current in one unit, which is derived by the geometric strength for the supply of the coils to generate the sum of the external magnetic field and the magnetic compensation field. see interference field is formed.

According to the invention, at the point where this is very annoying if the actual measuring head is located very precisely, a field and its changes corresponding to the strength of the measurements of the field strength of the earth's own magnetic interfering fields, but opposite to that, will be directed Compensation field is generated and with the help of a special facility for the purpose of soil research, an ongoing self-compensation is made to enable precise measurement. The measurement - according to the invention the difference in the field strength of the earth's magnetic field can thus be carried out with a very large total magnetic field between the two points X accuracy. It should be mentioned that 45 and Y are determined (at which the field strength of the compensatory external field provided according to the invention is practically the same, sationsanprdnung from the circuit structure no difficulties while the field strengths of the magnetic interference field are reliable and different ), a control variable is generated that is reasonably priced. . a particular one due to this difference and thus to a current strength proportional to the magnetic interference field, drawing is shown on the 50 and is explained in more detail below and generated under control by this variable. It shows - a magnetic compensation field, which counter-. F i g. 1 in a schematic, partially cut-like direction to the magnetic interference field, a side view of an aircraft for the accommodation and whose strength is proportional to this size, a magnetometer, 55 to make this difference to zero. At the Aus-F i g. 2 a circuit diagram of a compensation exercise of this method is generated at the points X order 1, and 7 a magnetic compensation field,: FIG. 3 a circuit diagram of a core filter (band- which makes the difference between the entire magnetic pass filter) and ■ ... · .- ... fields at points X and Y to zero by F i g. 4 shows two characteristic curves of the core filter, from which the value of the total magnetic field at each of these points can be seen to have a significant effect on the value of the external magnet. . ·;., · <. ■■; , field is reduced, whichever of these two

; In Fig. 1 is schematically an airplane with its points being the same. ■ · ■ '...

Nose N, its trunk Fh, its wings L, its when measuring the field strength of the magnetic field '

Control fins G of the tail unit Em and its 65 in X or in Y by means of a magnetometer head

Tail Q shown. As is well known, the greatest value of this measurement is that of the field strength of the

Part! the on-board devices (motors, electric and electromagnetic external field, which of the ironic equipments, holds, storage containers magnetic interference field is exempt from errors.

This method can advantageously be carried out with an inventive method shown in FIG. 2 shown device be exercised.

The device has devices Z which generate an electric current with a strength i proportional to the difference in the total magnetic field at two points X and Y , as well as coils 16 and 17 made of a conductive wire and conductor 18, 19 for feeding the coils 16, 17 with the current j, the distance between these coils 16 and 17 from the point M ₁ and the coefficient of proportionality between the current! and this difference is chosen so that the coils generate a magnetic compensation field which makes this difference zero.

The arrangement Z can expediently have two magnetometer heads with magnetic resonance, which are arranged at X, where the field strength of the entire magnetic field is H ₁ , or at Y, where the field strength of the entire magnetic field is H ₂ .

The head T ₁ arranged at X is expediently formed by a spin oscillator of the type described in French patent 1,351,587. Such an oscillator supplies a voltage at E ₁ , F ₁ with a frequency which is exactly proportional to the field strength of the entire magnetic field at point H _1. Such a head essentially contains a core filter T _{0 of} the type shown in FIG. 1-3 and described in more detail below, and an amplifier 11a without phase distortion, part of the output of this amplifier being fed back to the core filter through conductor 12. FIG.

The second head T _{2 located} at point Y is a more detailed one in FIG. 3, whose input variable applied at A, B is formed by a fraction of the output variable of amplifier 11a and thus of head T ₁ , while its output variable available at C, D is amplified in amplifier 11, whereupon this amplified output variable is amplified at C ₁ , D _{1 is} available.

The in Fig. 3 core filter of head T ₂ (and also of head T ₁ ) has two input terminals A, B (A ₁ , B ₁ for T ₀ ), between which an input coil 1 and a resistor 2 with purely ohmic impedance are connected in series , which is considerably greater than the impedance of the coil 1, so that the voltage U ₀ of the sinusoidal input signal applied to the terminals A, B is practically in phase with the likewise sinusoidal current / _{0 flowing through the coil 1.}

An output coil 3 and a resistor 6 are connected in series with the output terminals C, D supplying the output voltage U _1.

The coils 1 and 3 are normally decoupled, but they are coupled by a spin system (which forms part of a liquid 8 contained in a container 7). This spin system couples the output coil 3 to the input coil 1 with the resonance frequency of this spin system in the magnetic field (H ₂ for the head T ₂ ) in which it is placed, this resonance frequency, called noise frequency, being proportional to the field strength of the magnetic field.

The training is made so that the resonance frequency of the resonance circuit 5 of the Larmor frequency very obvious, the low quality factor of the resonance circuit 5 reducing the frequency entrainment should, d. H. is to prevent the resonance circuit 5 its resonance frequency from the output of the Filters.

In Fig. 3, a solution is used as liquid 8 which, in addition to the above spin system, contains a paramagnetic substance which allows the Overhauser-Abragam effect to be exploited if one of its electronic resonance lines is saturated by means of a coil 10 which is generated by an oscillator 9 with this resonance frequency is fed.
In the lower part of FIG. 4 the resonance curve of the spin system of the liquid 9 is shown, which couples the coils 1 and 3 with the resonance frequency / o, and in the vicinity of this frequency the width of the resonance band is denoted by d /. This upper part shows the changes in the amplitude α of the output voltage U ₁ as a function of the frequency / input voltage U ₀ (assuming that the amplitude of U _{0 is kept} constant and only its frequency / is changed).

The characteristic is a Lorentz curve, the greatest amplitude / η of which corresponds to the frequency /).

In the lower part of FIG. 4, again as a function of / and corresponding to the upper part of this figure, the phase shift ψ is shown. This is zero for / ₀ and fluctuates between - ^ - and -y- if / fluctuates between the values J ₁ and f ₂ , for which α becomes zero.

In the circuit of FIG. 2, the comparison of the phases of the available from E _1, F ₁ signal U ₀ and available in C _1, D ₁ signal U ₁ takes place in the phase discriminator 13. If the magnetic field H ₂ at Y is equal to the magnetic field H ₁ at X, the phase discriminator 13 supplies a voltage zero. However, this voltage becomes positive (or negative) as H ₂ increases (or decreases) from H _1. The sensitivity is very high because the phase angle between - ~ - and - -tr- for small changes in H ₂

fluctuates from H _1. This allows the points X and Y to approach each other with their distance dx z. B. is of the order of 50 cm, which is beneficial because the equality of the shape of the magnetic disturbances at X and Y is favored.

A voltage is thus obtained at the output of the unit 13 which is a function of the difference in the magnetic field between the points X and Y and, after amplification in an amplifier (not shown), is converted in the unit 15 into a current j, which corresponds to the difference between the magnetic field strengths H ₁ and H _{2 is} proportional (if this difference is small, that is, in the approximately straight section of the curve representing the change in φ iri near zero and practically in. the bandwidth /), and it is this current i which, as stated above, is fed to the coils 16 and 17, the axes of which are expediently arranged perpendicular to one another and to the plane of symmetry of the aircraft (plane of FIG. 1).

The circuit of FIG. 2 also supplies a voltage at E ₁ , F ₁ with a frequency proportional to the field strength of the magnetic field H _2. One to the

7 8

Points E ₁ , F _{1 of} connected frequency meter 14, so one finally obtains approximately: thus enables the determination of the field strength H ₂ ,

which the through arranged in the zone R "_" _ m_ _ (1 + 3p) - 1 _ m_ 3dx

Apparatus generated interference is corrected as this ^{x Y} ~~ ~ k χ ³ ~~ X χ * ' *'

has already been specified and more precisely below 5

is explained. In order to show more clearly how the grain- This measured value of H _x - H _Y is called

compensation of the magnetic interference fields is going on, "negative feedback" by the _one arranged at M 1

these and their compensation are to be introduced below coils 16 and 17. That from these coils

be calculated. Total field generated is immediate to this value

With the designations io proportional and has the value.

χ = distance from the magnetic center of gravity M ·,.

from the point Z, where the first head T _{1 r} - ^ - r,

(Fig. 1) is located, / ex

dx = distance between X and Y at which. . . ",. . _r , _cc ■. ■.

the two magnetometer heads T _1, T ₂ are ^{I5 where "n} '" ^{em "e} g ^ativer loop coefficient, st ·.

(Fig. 1 and 2) ^{ie from} this new compensation field

3, = distance between point M ₁ , at which touching magnetic field difference at points X

the compensation coils angeord- 16 and 17 ^and amounts ·

net, and point X (F i g. 2), and ^ j ^ a '

k = product ^ r ₁ U ₀ (where μ _{0 is} the coefficient of (H _X ) _C - (H _Y ) _C = -η- ■ ^ - r - £ - . (2)

Coulomb's equation for the magnetic / ex y

Mass, ie the magnetic permeability ^ ~, «o ir ruu uj ·

the vacuum) inventive method aims the

. Cancellation of the difference between the total

one obtains for any magnetic, at which 25 magnetic fields (which of the magnetic masses point M arranged disturbance mass m a magnetic one with the center of gravity M and the disturbance field arranged at M ₁ at X, which originate from coils 16 and 17, ie

HWl l tttti / tt \ / tj \

x - T '~~ T n _x - M _Y + (H _x ) _c - (ti _Y ) _c ,

/ ex 3 °

is, and a magnetic interference field at Y, which is the same which is the same:

/ 11 3dx m 3dx 3dx

k (x + dx) ³ ■>"^ i_-r.—. _r -

^y '35 k χ k x ⁴ y

is. ■

The difference between these two magnetic One wants to satisfy the following equation: Interference fields is given by the following formula:

1 1 N 40. k x ⁴ V TJ

it should be noted that in order to satisfy equation (3), the

Relationship apply:

(x + dx) ³ = x ³ ( i + -V. ⁴⁵

Zr άχ ,

j .. Λ = 1

If you put = p, you get

_m n α. p) 3 So we see that if y and dx are fixed, then one

Ηγ - H _x = -j- ■ ■ -5. can always find a coefficient r, which the

total magnetic field difference between points X

When developing the expression ττ ^ -ττ into one and / makes zero.

U + P) 55 A second condition requires that the field be on

MacLaurin's series or the series of the binomial of the point X remains constant. If H _{0 is} the value of the earth's magnetic field and H _{T is} the total of that

Head T ₁ is the value measured at X, one obtains

1 H = H ± ^m

= 1 + 3p + 6p ² + 10p ³ . 60 ^T ° ic ■ x ³

(1 + Pf

without compensation and

When ρ = small, as is the case here

^X u - TJ , / m m 3dxr_ \

is (if e.g. χ = 10 m and dx - 0.5 m, then 65 n _T - n ₀ ± I ^ .. _{χ3 fc} ' _χ 4 ^) \?)

A 1 ' Jr

one —— == ^ 0-, and one finds that the third. _T,.

* ^ ". with compensation.

Expression is already negligible). ' The measurement is correct when the second expression

of equation (5) is zero. So you get the Bediimuna:

10

from which one finally obtains:

This second condition (6) compared with the first condition (4) results in χ = y, which then results

3 dx j

results.

If the center of gravity is shifted in relation to the compensation coils, the error introduced by a slight shift in the center of gravity can be calculated, whereby the distance y is fixed, while χ is not exactly equal to y , but equal to y ± dy (so that dy represents the shifts in the center of gravity ).

If one introduces this value of y into equation (6) and calls the error factor s, one obtains

s = 1

3 dx r

O 1

3 dx ■ r
7 (1 ± q)

dy
if one puts: —— = q.

Maintaining the condition
H _x -Hy = O

now requires

from which results:

3dxr

s = l-

1 ± q

If q is small, then can

τ,
1 ± q

developed in a row

become, which after canceling after the second expression (since the third is negligible) results:

If z. It is assumed, for example, that the center of gravity M shifts by ± 0.5 m around the point M ₁ at which the coils 16 and 17 are located, the distance y being equal to 10 m (as is the case with Breguet on board an aircraft Atlantic made

Attempt was the case), one obtains - ^ = -, i.e. H.

y 20

for changes of 2 y (Iy = 10 ~ ⁵ Oersted) a maximum flow of 0.1 γ, which is quite acceptable. Incidentally, it has been found that the center of gravity M of the induced permanent magnetic fields shifts little in a flying aircraft when the load is fixed.

Finally it should be noted that in the above calculations the projection of the interference field vector onto do not change the direction of the earth's magnetic field

as this is unnecessary as it is _{the same for the two heads T 1} and T ₂ when the final result is multiplied by the cosine of the angle between the interference field vector and the direction of the magnetic field.

The arrangement not only allows the compensation explained above to be carried out thanks to the Feedback loop between the phase discriminator 13 and the magnetic compensation field generating coils 16 and 17, but also the

Determination of the field strength of the magnetic field by means of the frequency meter 14, this field strength of the disturbances originating from the magnetic interference fields is freed, with a very large one Accuracy.

As a modification, the magnetometer head T ₁ , the output of which is connected to the frequency meter 14, can be arranged at the point Y furthest away from the magnetic center of gravity M so that the influence of the remaining magnetic interference field on the frequency measured by the frequency meter is further reduced will; the head T ₂ is placed at X in this case.

1 sheet of drawings

Claims (3)

Patent claims 1. A method for compensating self-interference magnetic fields in an aircraft, which carries a magnetometer for measuring the field strength of an external magnetic field, in particular the magnetic earth field, characterized in that the difference in the field strengths of the entire magnetic field at two points (X, Y) of the vehicle is determined, where the field strength of the external magnetic field is about the same, on the other hand the field strengths of the magnetic self-interference field are different, that a current strength proportional to the difference between these field strengths and thus the magnetic self-interference field is generated as a control variable and that with the help of this control variable on the Point at which the measuring head of the magnetometer is located, a magnetic compensation field is created which is directed in the opposite direction to the self-interference magnetic field and has approximately the same field strength as the self-interference field. 2. Arrangement for compensating self-interference magnetic fields in an aircraft for performing the method according to claim 1, characterized in that the two points (X, Y) in the perpendicular plane of symmetry of the aircraft on the axis of the same one behind the other in the vicinity of the aircraft tail (Q), are preferably arranged at a mutual distance of a few centimeters and that in order to generate the compensation field two coils (16, 17) arranged near the center of gravity (M) of the magnetic masses of the aircraft are provided, the axes of which coils with the axis of the aircraft form three right angles. 3. Arrangement according to claim 2, characterized in that a magnetometer head (T ₂ ) is arranged at one of the points (X, Y) , which supplies a first voltage with a frequency proportional to the field strength of the magnetic field at this point, that a with this voltage applied frequency meter (14) to determine the field strength of the external magnetic field with compensated self-interference field is provided that at the other point (X or Y) a magnetometer head (T ₁ ) with a core filter (T ₀ ) (bandpass filter) is arranged, which is at his The input receives a portion of the first voltage and supplies a second voltage which is phase-shifted with respect to the first voltage by an angle which is proportional to the difference in the field strengths of the total magnetic fields at the two points (X, Y); and that a unit (13) is provided which receives the two voltages and supplies a third voltage proportional to the phase shift angle, of which a proportional current strength in a unit (15) is used to feed the coils (16, 17) for generating the compensation field is derived.