DE19717496C1 - System for magneto=optical current e.g. direct current (DC) measurements, with at least one light source - Google Patents

Abstract

The system for magneto-optical current measurement requires at least one light source (6) and a magneto-optical current sensor (5), which has at least 1....4 optical channels (1,2,3,4), for the transmitting of linear polarised light beams respectively with a polariser (P1,P2) connected before the current sensor with a specified polariser angle (alphai), with i = i...4 = channel number, and an analyser (Pa,Pb;TPa,TPb) connected after the current sensor, with a specified analyser angle (betai) which differs from the respective polariser angle (alphai). Each analyser on the output side, stands in an optical combination with a light detector (Da,Db) which delivers electrical signals (S1...S4) proportional on the output side to the received light power. For the polariser angle (alpha1,alpha2,alpha3,alpha4) and the analyser angle (beta1,beta4) the following relationships are valid; a) alpha3 = beta2, beta3 = a2 - pi/2 b) alpha4 = beta1 + pi/2, beta4 = alpha1 c) alpha1 - beta1 = alpha2 - beta2 and d) each angle pair (alpha1,beta1) is replaceable by an angle pair alpha1\!pi/2, betai + pi/2.

Description

Technical field

The invention is based on a method and from a device for magneto-optical current measurement the preamble of claims 1, 11 and 12.

State of the art

With the preambles of claims 1, 11 and 12 takes the invention related to a prior art as it from DE 43 42 410 A1 is known. There is a magnetoopti cal current measuring device specified, in which two ortho gonally polarized light beams in time or Frequency division multiplexed by a current sensor and analyzed at the output under ± π / 4. By two quotient formation from the output signals with Alternating and constant light components become the services of Light sources, the transmission factors and the detector temp sensitivities eliminated. However, essential sturgeon influences by dynamically and quasi-statically varying li linear voltage birefringence not compensated.

Presentation of the invention

The invention as defined in claims 1, 11 and 12 ned, solves the task, a procedure and a Vorrich to specify magneto-optical current measurement, which so probably a compensation of the linear double voltage  interferences caused as well as for equals current measurements is suitable.

Advantageous embodiments of the invention are in dependent defined gene claims.

An advantage of the invention is that the influence quasi-static and dynamically induced linear voltage birefringence on the power of the light signal largely is compensated and the magneto-optical current measuring device Therefore, both slow and fast measurement mechanical disorders reacted insensitively.

Another advantage is that the insensitive against slow and fast fluctuations in light conditions, transmission factors and detector sensitivity is so far improved that the invention is a disturbance free and accurate AC and DC measurement for both Protection purposes (broadband monitoring for over stream) as well as for billing purposes (narrowband Current measurement for the calculation of electrical power) light.

Another advantage of the invention is that meh more combinations of polarizer analyzer positions variable angle difference between polarizer and analyzer can be realized.

An additional advantage is that the sensor signals birefringence due to interference and transmis tion change can be determined quantitatively.

Brief description of the drawings

The invention is illustrated below with reference to embodiments play explained. Show it:  

Fig. 1 a first embodiment of the present invention s current measuring device,

Fig. 1a shows an alternative embodiment of a component of the current measuring device according to Fig. 1 and

Fig. 2-4 second to fourth embodiments of a current measuring device according to the invention.

Ways of Carrying Out the Invention

The following are the theoretical foundations of Erfin briefly summarized.

A beam of light is transmitted through a polarizer with a pola Risation angle α linearly polarized and by a current sensor, e.g. B. a vitreous or a glass fiber, ge sends and in the end through an analyzer with a polar sationswinkel β analyzed. The current sensitivity of the Glases is based on a magnetic field-induced circular Birefringence (magneto-optical or Faraday effect). At additional presence of a homogeneously distributed linear Birefringence in the current sensor can result in lei or a light output proportional to Si gnal S (α, β) - based on a publication by W. J. Tabor and F. S. Chen: Electromagnetic Propagation through Materials Possessing both Faraday Rotation and Birefrin gence: Experiments with Ytterbium Orthoferrite, J. Appl. Phys. 40, No. 7 (1969), pp. 2760-2765, after a longer calculation followed and skillful summary of the terms of the formula:

S (α, β) = I₀ / 2 [1 + cos (2 · (α - β)) · cos δ + sin (2 · (α - β)) · sin δ · sin χ + cos (2 · (α - ψ)) · cos (2 · (β - ψ)) · (1 - cos δ) · (cos χ) ²] (G1)

It is

with θ = V · I, V = Verdet constant, I = current for the rotation angle, Γ = caused by linear birefringence (mean) phase shift and ψ = (mean) orientation the fast birefringence axis in the current sensor. I₀ summarizes the power or strength of the light source, the trans mission coefficients and the sensitivity of the detector including an electronic signal amplification. All Polarization angles α, β have a period of π, d. i.e. it applies: α + π = α and β + π = β; you will be regarding most coordinates, d. H. regardless of the beam direction, measured. In the following, apply -π / 2 <α, β π / 2.

With C (α, β) = cos (2 (α - β)) cos δ,
A (α, β) = 2 · sin (2 (α - β)) · (sin δ) / δ and N (α, β, ψ) = cos (2 · (α - ψ)) · cos (2 · (β - ψ)) · (1 - cos δ) · Γ² / δ² is equation (G1)

S (α, β) = I₀ / 2 · [1 + C (α, β) + A (α, β) · θ + N (α, β, ψ)] (G2)

The 1st term 1 + C denotes a constant light component, the 2. Term or usage term A · θ changes in intensity by the  Faraday effect and the 3rd term or disturbance term N changes due to linear birefringence.

Apparently, all of the functions listed above apply C (α, β), A (α, β) and N (α, β) the following relations:

F (α ± π / 2, β ± π / 2) F (α, β) and (G3a)
F (α ± π / 2, β) = F (α, 13 ± π / 2) = -F (α, β) (G3b)

From equation (G3a) it follows that arrangements that only by rotating the polarizer and the analyzer together on a theoreti level are completely equivalent. Equation (G3b) states that all functions change sign if either the polarizer or analyzer is rotated by π / 2.

If polarizer and analyzer angles are interchanged however, that only the Faraday effect is the forerunner chen changes: The following applies:

C (β, α) = C (α, β) (G4a)
A (β, α) = -A (α, β) and (G4b)
N (β, α) = N (α, β) (G4c)

Furthermore, C (α, β) and A (α, β) depend only on the difference between between the two angles and are therefore invariant under joint rotation of the polarizer and analyzer kels.

The invention task, a largely trouble-free mag netooptical current sensor for exact measurement of both Specifying alternating and direct currents is thereby ge resolves that multiple optical channels are created and out of their  Signals a trouble-free current signal with alternating and DC component is extracted. The optical channels are there especially with their polarizer and analyzer win kel and the arrangement of the optical feed and Wegfa characterized. The disturbances to be eliminated hit dynamic and (quasi) static light in particular power fluctuations due to noise and drift of the light source (s), by birefringence in the current sensor, by Bie supply and exit fibers and by variation or Drift of the transmission of optical components as well as the De tector sensitivity and electronic gain. In addition, an optical activity as z. B. in a twisted sensor fiber occurs, are eliminated, if optical channels with pairs of opposite light direction of propagation can be used in the current sensor. In in this case the optical activity behaves with respect to the angular exchange relationships (G4) the same as the linear birefringence term N.

In a first step, the polarizer and analyzer angles are determined which allow the elimination of the interference term N. It is output from a 4-channel current sensor, from its light output proportional signals S _i (i = 1,..., 4) by forming a quotient Q = (S₁ · S₄) / (S₂ · S₃) or a difference D = S₁ + S₄-S₂-S₃ a current is to be determined. It is then required that under the general assumption that A · θ and N are relatively small compared to 1, the birefringence-induced interference signal is zero and a non-vanishing Faraday signal results:

N (α₁, β₁) + N (α₄, β₄) -N (α₂, β₂) -N (α₃, β₃) = 0 (G5)
A (α₁, β₁) + A (α₄, β₄) -A (α₂, β₂) -A (α₃, β₃) ≠ 0 (G6)
where α _i and β _i denote the polarizer and analyzer angles of the ith optical channel. Angular relationships that satisfy the conditions (G5) and (G6) can easily be found using the relations (G3) and (G4). From equation (G4) we get z. B. the solution:

α₃ = β₁, β₃ = α₁; α₄ = β₂, β₄ = α₂ (G7a)

with the additional condition α₁ - β₁ ≠ α₂ - β₂, swapping the indices 2 and 3 again results in a valid solution. With the help of equation (G7a) and the relation (G3b), a relationship between the optical channels ( 2 ) and ( 3 ) and between ( 1 ) and ( 4 ) can be found as an important solution:

α₃ = β₂, β₃ = α₂ - π / 2; α₄ = β₁ + π / 2, β₄ = α₁ (G8a)
again with α₁ - β₁ ≠ α₂ - β₂.

Other solutions arise when there are terms of two channels Store separately in (G5). Then we get analog to Glei chung (G7a) z. B. the solution:

α₃ = β₁, β₃ = α₁; α₄ = α₂, β₄ = β₂ (G7b)

with the index exchanges 2 with 3 or 1 with 4 or simultaneously 2 with 3 and 1 with 4 further solutions hen. One also finds analogous to equation (G8a)

α₃ = β₂, β₃ = α₂ -π / 2; α₄ = α₁ + π / 2, β₄ = β₁ (G8b)

with another solution through simultaneous index swapping 1 with 2 and 3 with 4. Of course, from all above solutions with equation (G3a) additional solutions ge be won.  

To determine a current signal, ei signal evaluation based on quotient formation, which are particularly useful for measuring alternating and direct current suitable is. Assuming that θ is small and esp special 2 · θ <Γ and thus approximately δ ≈ Γ applies simplified functions C (α, β), A (α, β) and N (α, β, ψ):

C (α, β) = cos (2 · (α - β)) (G9)
A (α, β) = 2sin (2 (α - β)) (sinΓ) / Γ (G10)
N (α, β, ψ) = -2sin (2 (α - ψ)) sin (2 (β - ψ)) (sin (Γ / 2)) ² (G11)

In the case of a large Faraday rotation θ, the useful term A · θ applies also the approximation:

 (α, β) = sin (2 · (α - β)) · (sin (2 · θ)) / θ (G10 ′)

It should be noted here that under the special advance settlement α - β = ± π / 4 the simplified quantities:

C = 0 (G12)
A = ± 2 · (sin Γ) / Γ or (G13)
 = ± (sin (2 · θ)) / θ and (G13 ′)
N (α, ψ) = sin (4 · (α - ψ)) · (sin (Γ / 2)) ² (G14)

receives. In addition, N (α, ψ) = - N (α + π / 4, ψ), un depending on the approximation (G11).  

In a 4-channel arrangement, the light powers or electrical signals S _i with the notation C _i = C (α _i , β _i ), A _i = A (α _i , β _i ) and N _i = N (α _i , β _i , ψ) with i = 1,. . ., 4, for the approximations (G9) - (G11) and arbitrary angles α, β are written as follows:

S₁ = I₀₁ · (1 + C₁ + A₁ · θ + N₁) (G15a)
S₂ = I₀₂ · (1 + C₂ + A₂ · θ + N₂) (G15b)
S₃ = I₀₃ · (1 + C₃ + A₃ · θ + N₃) (G15c)
S₄ = I₀₄ · (1 + C₄ + A₄ · θ + N₄) (G15d)

where I _0i in turn _summarizes the light output of the light source, the transmission and the detector sensitivity of the i-th optical channel. The same relationships apply to sizes _{i i} . Under the assumptions C _i <1 that can practically always be fulfilled and because of θ, Γ <1 also A _i · θ, Â _i · θ, N _i <1, the quotient Q is in a first approximation:

Q = (S₁ · S₄) / (S₂ · S₃) = b · [1 + (A₁ + A₄) · θ] / [1 + (A₂ + A₃) · θ] = b · [1 + (A₁ - A₂ - A₃ + A₄) · θ] (G16)

With θ = V · I and the prefactor b = (I₀₁ · I₀₄) / (I₀₂ · I₀₃), the sen factors I₀₁,. . . I₀₄ in the absence of a current I from the signals S₁,. . ., S₄ and the equations (G15) are determined according to the relationships I _0i = S _i / (1 + C _i + N _i ), can be found in the approximations (G10) and (G10 ') for the current I in particular the evaluation formulas:

I = [Q / b - I] / [V · (A₁ - A₂ - A₃ + A₄)] or (G17)
I = 1 / (2 · V) · arc sin [(Q / b - 1) / (Â₁ - Â ₂ - Â₃ + Â₄)] (G17 ′)

In a second step, the interference of the light source (s), the light transmission path and the detectors on the current signal to be obtained should be minimized or eliminated. Some optical configurations for solving this problem are given in the exemplary embodiments, from which there arise additional, more practical restrictions for the above angular relationships (G7a), (G7b), (G8a) and (G8b). For very good interference suppression, a maximum of 2 light sources, 2 feed fibers, 2 routing fibers and 2 detectors may be used with 4 optical channels ( FIGS. 1, 2). With 8 optical channels, up to 4 routing fibers and 4 detectors are also permissible (FIGS . 3, 4). The feed fibers are advantageously highly birefringent, polarization-maintaining monomode fibers, which each transport a pair of orthogonally polarized input light beams to the sensor, so that:

α₂ = α₁ + π / 2; α₄ = α₃ + π / 2 (G18)

On the other hand, the use of only two leads fiber in the 4-channel system, that applies:

β₁ = β₂; β₃ = β₄ (G19)

Under the conditions (G18) and / or (G19) only the Relationship (G8a) an angular solution with non-vanishing This solution then depends only on the Angle of the 1st channel (α₁, β₁) from:

α₂ = α₁ + π / 2, β₂ = β₁ (G20a)
α₃ = β₁, β₃ = α₁ (G20b)
α₄ = β₁ + π / 2, β₄ = α₁ (G20c)

The channels are so through the following polarizer analyzer Characterized couples:

Channel 1 : (α₁, β₁),
Channel 2 : (α₁ + π / 2, β₁),
Channel 3 : (β₁, α₁),
Channel 4 : (β₁ + π / 2,: α₁),

where 0 ≠ | α - β | ≠ π / 2, but the angles are arbitrary are selectable.

An equivalent angular configuration can also be generated based on the relation (G3b) by rotating the polarizer and analyzer in channels 2 and 4 by π / 2:

Channel 1 : (α₁, β₁),
Channel 2 : (α₁, β₁ + π / 2),
Channel 3 : (β₁, α₁),
Channel 4 : (β₁, α₁ + π / 2).

This configuration has only two different polarizers angles, but four different analyzer angles. In the Pra xis should all the angular relations mentioned with a Ge accuracy of ± 0.1 rad or better.

Some exemplary embodiments are set out below.

For the practical execution of current measurement according to the invention devices will preferably be the first of the above orders used according to equations (G20a) - (G20c). For example, you can also choose | α₁ - β₁ | = π / 4, in particular α₁ - β₁ = π / 4, meet who also the Ausfü examples. The evaluation formulas (G17) or (G17 ′) are then simplified because of (G13) or (G13 ′):

I = [Q / b - 1] / [8V · (sinΓ) / Γ] or (G21)
I = 1 / (2 · V) · arc sin [(Q / b - 1) / 4] (G21 ′)

In the exemplary embodiments, α 1 = π / 4 was also ge sets, so that the channels characterize by the following angles are:

Channel 1 : (π / 4, 0),
Channel 2 : (-π / 4, 0),
Channel 3 : (0, π / 4),
Channel 4 : (π / 2, π / 4).

According to the first embodiment ( Fig. 1) 4 channels ( 1 , 2 , 3 , 4 ) are realized by light rays, which a current sensor ( 5 ), the z. B. is designed as a solid optical glass block, run in the same direction. They are generated by a light source ( 6 ), which comprises two laser diodes (LD₁, LD₂), which initiate orthogonal to each other linearly polarized light beams into two highly birefringent, polarization-maintaining fibers, which together form a non-polarizing beam splitter ( 7 ), e.g. B. a polarization-maintaining fiber coupler, where they are in turn via two highly birefringent polarization-maintaining fibers ( 8 a), ( 8 b) and collimators the current sensor ( 5 ) leads. The fiber ( 8 a) is twisted by -π / 4, so that the light rays of the channels ( 1 ) - ( 4 ) as indicated above and indicated in Fig. 1, the polarizations π / 4, -π / 4, 0 and π / 2.

The light beams of the channels ( 1 ) and ( 2 ) are fed through a first polarization filter (P _a ) with the analyzer angle 0 via output-side collimators and fibers ( 9 ) to a photodiode (D _a ) as a light detector, which is proportional to the power of the light beam , Not shown output signals S₁, S₂ generated. Light rays of the channels ( 3 ) and ( 4 ) fall through a polarization filter (P _b ) with the analyzer angle π / 4 over fibers ( 9 ) on a second photo diode (D _b ) and cause output signals S₃, S₄ not shown there. The signals S₁, S₂ and S₃, S₄ can each by a multiplex method, for. B. by time, frequency or wavelength division multiplexing of the two LEDs (LD₁, LD₂), separated. It is advantageous to use as feed fibers ( 8 a), ( 8 b) bend-insensitive polarization-maintaining monomode fibers and as routing fibers ( 9 ) bend-insensitive multimode fibers. This guarantees a high and vibration-insensitive light coupling through the glass block current sensor ( 5 ), since the small core of the monomode fibers ensures very good collimation and the relatively large core of the multimode fibers ensures a large light receiving area. Also, it is advantageous if the numerical aperture of the output collimators is selected smaller than the numerical aperture of the return fibers (9), in order to minimize the excitation extremely flexurally sensitive cladding modes (cladding modes) in the fibers (9). Furthermore, the fibers ( 8 a, 8 b, 9 ) should have a low sensitivity to bending particularly when very long distances, for. B. 1 km and more, must be bridged or the routes are severely disturbed by mechanical shocks. It is shown below that the Mehrka channel arrangements according to the invention can also compensate for any remaining disturbing light egg fluctuations very effectively.

The light source ( 6 ) can also be carried out as shown in Fig. 1a, where the light from a single laser diode (LD) by two orthogonally set polarization filters (P₁, P₂) and modulators (M₁, M₂) - z. B. scarf ter - the non-polarizing beam splitter ( 7 ) are supplied.

When evaluating the signals, it is known that the problem arises that the signals are not fully controllable different factors, which - in the case of the embodiment according to Fig. 1 - both the generally un different light intensities of the laser diodes (LD₁, LD₂), Distribution ratio of the beam splitter ( 7 ) and the coupling into the current sensor ( 5 ) as well as differences in the coupling out of the same, the sensitivities of the photo diodes (D _a , D _b ) and their electronic amplifications.

A known solution to this problem is the separation of AC and DC components and the adjustment of said factors by dividing the former by the the latter in each channel (ac / dc method). This Auswer However, this method is unsuitable for direct current measurements because quasi-static variations of the constant light component by the Division be regulated, regardless of whether it through variable optical transmission power (s), light transmissions and detector sensitivities or through DC currents are caused.

Accurate AC and DC measurement for both Protection as well as billing purposes can however be approved nete processing of the four Sig obtained according to the invention nale can be achieved. For this purpose, quotients from the signals formed in which the disturbance variables drop out, according to

Q₁₃ = S₁ / S₃ = I₀₁ / I₀₂ · (1 + N + A · θ) / (1 + N - A · θ) (G22)

Assuming that A · θ and N are relatively small compared to 1, so they become dyna mix and quasi-static fluctuations in light output vibration or static stress birefringence eliminated according to

Q₁₃ = I₀₁ / I₀₃ · (1 + 2 · A · θ) (G23)

The factor I₀₁ / I₀₃ in Q₁₃ is also independent of the transmission power and the noise of the light source (LD₁), but depends on the ratio of the sensitivities of the photodiodes (D _a , D _b ), since the channels ( 1 ) and ( 3 ) supplied by the same light source, but received by different photodiodes. The same applies to a quotient

Q₂₄ = S₂ / S₄ = I₀₂ / I₀₄ · (1 - N - A · θ) / (1 - N + A · θ) = I₀₂ / I₀₄ · (1 - 2 · A · θ) (G24)

From the double quotient

Q = Q₁₃ / Q₂₄ ≈ (I₀₁ · I₀₄) / (I₀₂ · I₀₃)) · (1 + 4 · A · θ) (G25)

However, the detector ratio also falls out, so that Q depends neither on the light sources (LD₁, LD₂) nor on the photodiodes (D _a , D _b ). In addition, the ratios I₀₁ / I₀₂ and I₀₄ / I₀₃ ensure that dynamic and quasi-static transmission fluctuations behind the beam splitter ( 7 ), in particular by fiber bending and light coupling by the current sensor ( 5 ), are largely eliminated.

The prefactor b = (I₀₁ · I₀₄) / (I₀₂ · I₀₃) can, however, deviate from 1 if the distribution ratio of the beam splitter ( 7 ) is polarization-dependent, ie the light output between the channels ( 1 ) and ( 3 ) is not distributed exactly the same becomes like between channels ( 2 ) and ( 4 ). However, this can be determined by a measurement and compensated for by taking the pre-factor b into account. It should then also be noted any temperature drift of the pre-factor b due to different temperature dependencies of the splitting conditions for orthogonally polarized beams. Such a temperature drift can be compensated for by temperature stabilization of the beam splitter ( 7 ).

Influences of any wavelength shifts, as can be caused by temperature changes in the light emitting diodes (LD₁, LD₂), can be avoided by executing the light source according to FIG. 1a, where all channels are supplied by the single light source (LD).

The second embodiment according to FIG. 2 corresponds in principle to the first already described in connection with FIG. 1, but the channels ( 1 ), ( 3 ) and ( 2 ), ( 4 ) each form pairs with the opposite direction of radiation through the current sensor ( 5 ) and go on both sides through beam splitters (T _a , T _b ), which, if necessary, can be used to correct birefringence effects in (T _a ) or (T _b ) birefringent elements on the output side. In this arrangement, the light paths of all channels in the current sensor ( 5 ) are identical, so that influences of local differences in the optical properties of the current sensor ( 5 ) are excluded. Any circular birefringence or optical activity that may be present is also eliminated. The evaluation is carried out exactly as described in connection with the first embodiment example. The light source ( 6 ) can also be designed as in Fig. 1a.

The third embodiment according to FIG. 3 corresponds in principle to the first structure according to FIG. 1. However, the analysis of the light beams is not carried out by polarization filters, but by means of polarizing beam splitters (TP _a , TP _b ), which orthogonally divide the light beams into two divide other polarized components, which are each fed to two photodiodes (D _a , D _a ') and (D _b , D _b '). In addition to the four channels ( 1 ) - ( 4 ) of the first embodiment, four further channels ( 1 ′) - ( 4 ′) with the following polarizer and analyzer angles are created analogously to (G20a) - (G20c):
Channel 1 ′: (α₁, β₁ + π / 2),
Channel 2 ′: (α₁ + π / 2, β₁ + π / 2),
Channel 3 ′: (β₁, α₁ + π / 2),
Channel 4 ′: (β₁ + π / 2, α₁ + π / 2)

or under the restrictions α₁ - β₁ = π / 4 and α₁ = π / 4

Channel 1 ′: (π / 4, π / 2),
Channel 2 ′: (-π / 4, π / 2),
Channel 3 ′: (0, -π / 4),
Channel 4 ′: (π / 2, -π / 4).

If you evaluate the output signals of channels S₁ - S₄ exactly same as in connection with the first execution example described and the output signals S₁'-S₄ 'the other channels analog, so you get in addition to (G25)

Q ′ = Q₁₃ ′ / Q₂₄ ′ = ((I₀₁ · I₀₄) / (I₀₂ · I₀₃)) · (1 - 4 · A · θ) (G26)

and it

q = Q / Q ′ = [(S₁ · S₄) / (S₂ · S₃)] / [(S₁ ′ · S₄ ′) / (S₂ ′ · S₃ ′)] = (1 + 8A · θ) (G27)

The pre-factor b and thus the ratio of the distribution ratios for orthogonal polarizations at the beam splitter ( 7 ) also fall out of this equation and the current is found

I = [q - I] / [16 · V · (sin Γ) / Γ] (G28)

A general evaluation formula for any α and β can be found one in direct analogy to (G17) or (G17 ′) according to

I = [q - 1] / [V · R] or (G29)
I = 1 / (2 · V) · arc sin [(q - 1) / r] (G29 ′)

where R = A₁-A₁ ′ + A₄-A₄ ′ - (A₂-A₂ ′ + A₃-A₃ ′), r = Â₁-Â₁ ′ + Â₄-Â₄ ′ - (Â₂-Â₂ ′ + Â₃-Â₃ ′) and the deleted sizes refer to the channels ( 1 ') - ( 4 '). For a non-vanishing benefit, the equation (G29) and (G29 ′) must apply Q ≠ Q ′. This can be achieved if at least one difference angle α _i ′ - β _i ′ of the channels ( 1 ′) - ( 4 ′) deviates from the corresponding difference angle α _i -β _{i of} the channels ( 1 ) - ( 4 ). In particular, for the same polarizer angle α _i ′ = α _i with i = 1,. . ., 4 different analyzer angles β _i ′ ≠ β _i can be selected. In this case, a generalized polarizing beam splitter (TP _a , TP _b ) with two freely adjustable analyzer angles can also be used. Such a beam splitter can, for. B. can be realized by combining a non-polarizing beam splitter with orientable polarizers at both outputs.

The fourth embodiment according to FIG. 4 connects the analysis under additional analyzer angles according to the third with the change in the transmission direction according to the second embodiment. Not only are all undesirable factors influencing the result eliminated, the embodiment also offers a complete overlap of the light paths of the various channels in the current sensor ( 5 ) and the additional elimination of any circular birefringence or optical activity that may be present.

The general angular relations (G7a), (G7b) and (G8b) can of course as a basis for ge immune refraction-induced light fluctuations immune opti configurations are used.  

The exemplary embodiments according to FIGS. 1-4, however, are characterized by a particularly small number of optical elements and by beam guidance, which ensures extensive elimination of all slow and fast signal fluctuations caused by birefringence in the current sensor ( 5 ) Light source ( 6 ), caused by the fibers ( 8 a), ( 8 b), ( 9 ), by the light coupling by the sensor ( 5 ) and the detectors (D _a , D _a ', D _b , D _b ') will. It goes without saying that in the exemplary embodiments, general polarizer and analyzer angles may also be selected in accordance with equations (G20a) - (G20c).

The measures according to the invention enable extensive elimination of interference-related falsifications of the current signal. By non-ideal compensation of interference, however, at very high interference levels, e.g. B. by violent vibration of the current sensor ( 5 ) or the fibers ( 8 a, 8 b, 9 ), dynamic interference signals still occur. It is therefore desirable to know the disturbances quantitatively in order to be able to assess the reliability of the current measurement.

The invention makes it possible to measure individual dynamic disturbance variables separately with the aid of an additional signal evaluation. For this purpose, standardized signals s _{i are} formed by splitting each signal S _i into an alternating and a constant light component and dividing the alternating component by the equal component (ac / dc method). By forming the difference and sum of the standardized signals s _i , the vibration-induced birefringence N _{ac can be} according to:

N _ac = [s₁-s₂ + s₃-s₄] / 8 (G30)

and rapid transmission changes τ₁₂ or τ₃₄, in particular those caused by bending the fibers ( 8 a), ( 8 b) and ( 9 ), in channels ( 1 ) and ( 2 ) or ( 3 ) and ( 4 ) according to:

τ₁₂ = [s₁ + s₂] / 2 and (G31)
τ₃₄ = [s₃ + s₄] / 2 (G32)

determine.

With the 8 channel arrangements you get e.g. Belly

N _ac = - [s₁′-s₂ ′ + s₃′-s₄ ′] / 8 (G33)

and the rapid transmission changes τ₁₂ ′ or τ₃₄ ′ in channels ( 1 ′) and ( 2 ′) or ( 3 ′) and ( 4 ′) can take on other values because of the additional feedback fibers ( 9 ):

τ₁₂ ′ = - [s₁ ′ + s₂ ′] / 2 (G34)
τ₃₄ ′ = - [s₃ ′ + s₄ ′] / 2 (G35)

In the equations (G31), (G32), (G34) and (G35) two light signals s _i and s _{j are} summed up because the same optical channels i and j pass through and from a common detector (D _a , D _a ', D _b , D _b ') are received. In the 8-channel arrangements, the birefringence N _{ac can of} course also be determined using equation (G30) or a combination of equations (G30) and (G33).

Overall, the invention enables a dynamic and static interference excellent immune current measurement with egg a polarimetric Faraday current sensor.

Reference list

1-4 , 1'-4 ' optical channels
5 current sensor
6 light source
7 beam splitters, fiber couplers
8 a, 8 b (feed) fibers
9 (guide) fibers
LD, LD₁, LD₂ light emitting diode, laser diode
P₁, P₂, P _a , P _b polarization filter
M₁, M₂ modulators
D _a , D _b , D _a ′, D _b ′ detectors, photodiodes
T _a , T _b beam splitter
Tp _a , Tp _b polarizing beam splitters.

Claims (12)

1. Device for magneto-optical current measurement with at least one light source ( 6 ) and a magneto-optical current sensor ( 5 ), the at least four 1st . . 4. optical channels ( 1 , 2 , 3 , 4 ) for transmitting linearly polarized light beams, each with a current sensor ( 5 ) upstream polarizer (P₁, P₂) with a predetermined polarizer angle α _i , i = 1,. . ., 4 = channel number, and a downstream of the current sensor ( 5 ) analyzer (P _a , P _b ; TP _a , TP _b ) with a predeterminable analyzer angle β _i , which differs from the respective polarizer angle α _i , each analyzer on the output side with a light detector (D _a , D _b ) is in optical connection, the output side supplies electrical signals proportional to the received light power (S₁,..., S₄), characterized in that for the polarizer angle (α₁, α₂, α₃, α₄ ) and the analyzer angles (β₁, β₂, β₃, β₄) the following relations apply:

• a) α₃ = β₂, β₃ = α₂-π / 2,
• b) α₄ = β₁ + π / 2, β₄ = α₁,
• c) α₁-β₁ ≠ α₂-β₂ and
• d) that each angle pair α _i , β _{i can be} replaced by an angle pair α _i ± π / 2, β _i + π / 2.

2. Device according to claim 1, characterized in that for the polarizer angle (α₁, α₂, α₃, α₄) the following relations apply:

• a) α₂ = α₁ + π / 2 and
• b) α₄ = α₃ + π / 2.

3. Device according to claim 1, characterized in that for the analyzer angle (β₁, β₂, β₃, β₄) the following relations apply:

• a) β₂ = β₁ + π / 2 and
• b) β₄ = β₃ + π / 2.

4. The device according to claim 2, characterized in that

• a) each have two optical channels ( 1 , 3 ; 2 , 4 ) opposite to each other ent transmission directions,
• b) in particular that the first optical channel ( 1 ) and the third optical channel ( 3 ) and the second optical channel ( 2 ) and the fourth optical channel ( 4 ) each form a pair.

5. Device according to one of claims 1 to 4, characterized in that

• a) the light source ( 6 ) on the output side two light beams len with mutually orthogonal polarization lines (α₁, α₂) and
• b) that the two light beams can be detected separately using a multiplex method,
• c) in particular that each light beam is time, frequency or wavelength division multiplex detectable.

6. The device according to claim 5, characterized in that the light source ( 6 ) comprises two modulatable laser diodes (LD₁, LD₂), each emitting linearly polarized light in a polarization-maintaining fiber, which fibers are fed together to a beam splitter ( 7 ), of which Lead polarization-maintaining fibers ( 8 a, 8 b) to the current sensor ( 5 ). 7. The device according to claim 5, characterized in that the light source ( 6 ) contains two polarization filters (P₁, P₂), to each of which a polarization-maintaining fiber connects, which fibers are fed together to a non-polarizing beam splitter ( 7 ), of which polarization-maintaining fibers ( 8 a, 8 b) to the current sensor ( 5 ). 8. Device according to one of claims 5 to 7, characterized in that at least one analyzer is a po larizing beam splitter (TP _a , TP _b ) with two mutually perpendicular analyzer angles. 9. Device according to one of claims 5 to 8, characterized in that a beam splitter (T _a , T _b ) is arranged between the light source ( 6 ) and each light entry surface of the current sensor ( 5 ), which has an output with a light detector (D _a , D _b ) is in optical connection. 10. Device according to one of the preceding claims, characterized in that for the difference between the polarizer angle α₁ and the analyzer angle β₁ of the first optical channel ( 1 ) the relationship | α₁-β₁ | = π / 4 ± 0.1 rad applies. 11. Method for current measurement with a magneto-optical current sensor ( 5 ), with linearly polarized light beams from at least one light source ( 6 ) via at least four first . . . 4. optical channels ( 1 , 2 , 3 , 4 ) are passed through a current sensor ( 5 ) to at least one light detector (D _a , D _b ), these light beams on the current sensor ( 5 ) on the input side upstream Polarisa gates (P₁, P₂) with a predeterminable polarizer angle α _i with i = 1,. . ., 4 = channel number, pass through and on the output side an analyzer (P _a , P _b ; TP _a , TP _b ) connected downstream of the current sensor ( 5 ) with a predeterminable analyzer angle β _i , which differs from the respective polarizer angle α _i , pass and in the light detector (D _a , D _b ) for the received light power proportional electrical signals (S₁,..., S₄) generate gene, characterized in that

• a) α₃ = β₂, β₃ = α₂-π / 2,
• b) α₄ = β₁ + π / 2 and β₄ = α₁ is set with:
• c) α₁-β₁ ≠ α₂-β₂
• d) wherein each pair of angles α _i , β _{i can be} replaced by an angle pair α _i + π / 2, β _i ± π / 2, and
• e) that a current I to be measured according to:
  I = [Q / b - 1] / [V · (A₁-A₂-A₃ + A₄)]
  With
  Q = (S₁ · S₄) / (S₂ · S₃) and
  b = (I₀₁ · I₀₄) / (I₀₂ · I₀₃) is determined,
  where the I₀₁,. . . I₀₄ in the absence of a current I from the signals S₁,. . ., S₄ according to relationships
  I _0i = S _i / (1 + C₁ + N₁) can be determined,
  C _i = cos (2 * (α _i -β _i )),
  A _i = 2 · sin (2 · (α _i -β _i )) · (sin Γ) / Γ, N _i = -2 · sin (2 · (α _i - ψ)) · sin (2 (β _i - ψ)) · (sin (Γ / 2)) ²,
  Γ = phase shift induced by a linear birefringence, ψ = orientation of the fast birefringence axis and V = Verdet constant.

12. Method for current measurement with a magneto-optical current sensor ( 5 ), with linearly polarized light beams from at least one light source ( 6 ) via at least four first . . . 4. optical channels ( 1 , 2 , 3 , 4 ) are passed through a current sensor ( 5 ) to at least one light detector (D _a , D _b ), these light beams on the current sensor ( 5 ) on the input side upstream Polarisa gates (P₁, P₂) with a predeterminable polarizer angle α _i with i = 1,. . ., 4 = channel number, pass through and on the output side an analyzer (P _a , P _b ; TP _a , TP _b ) connected downstream of the current sensor ( 5 ) with a predeterminable analyzer angle β _i , which differs from the respective polarizer angle α _i , pass and in the light detector (D _a , D _b ) for the received light power proportional electrical signals (S₁,..., S₄) generate conditions, characterized in that

• a) α₃ = β₂, β₃ = α₂ - π / 2,
• b) α₄ = β₁ + π / 2 and β₄ = α₁ is set with:
• c) α₁-β₁ ≠ α₂-β₂
• d) wherein each pair of angles α _i , β _{i can be} replaced by an angle pair α _i ± π / 2, β _i 1 π / 2, and
• e) the light emerging from the current sensor ( 5 ) beams in polarizing beam splitters (TP _a , TP _b ) and divides via the second outputs to light detectors (D _a ', D _b ') which have four further 5 on the output side. . . . 8. generate electrical signals proportional to the received light output (S₁ ',..., S₄'),
• f) a current I to be measured in accordance with:
  I = [q - I] / [V · R]
  With
  q = [(S₁ · S₄) / (S₂ · S₃)] / [(S₁ ′ · S₄ ′) / (S₂ ′ · S₃ ′)] and R = A₁-A₁ ′ + A₄-A₄ ′ - (A₂-A₂ '+ A₃-A₃') is determined,
  where A _i = 2 · sin (2 · (α _i -β _i )) · (sin Γ) / Γ,
  A _i ′ = 2 · sin (2 · (α _i - (β _i ± π / 2))) · (sin Γ) / Γ,
  Γ = phase shift induced by a linear birefringence and V = constant constant.