CA2258231A1 - Temperature calibration process for an optical magnetic field measurement device and measurement device calibrated by this process - Google Patents
Temperature calibration process for an optical magnetic field measurement device and measurement device calibrated by this process Download PDFInfo
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- CA2258231A1 CA2258231A1 CA002258231A CA2258231A CA2258231A1 CA 2258231 A1 CA2258231 A1 CA 2258231A1 CA 002258231 A CA002258231 A CA 002258231A CA 2258231 A CA2258231 A CA 2258231A CA 2258231 A1 CA2258231 A1 CA 2258231A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/032—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
- G01R33/0322—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect using the Faraday or Voigt effect
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
- G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/005—Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
- Measuring Magnetic Variables (AREA)
Abstract
An optical series mounting (1) consists of a first optical transmission section (4), a first polariser (5), a Faraday sensor (3), a second polariser (6) and a second optical transmission section (7) which is temperature calibrated by adjusting in a particular manner the angle of polarisation of the two polarisers (5, 6). This calibration process works even when the inherent axis of linear birefringence in the sensor is not known.
Description
FiLL~r'~
Speciflcation Method f~r Temper~ture Calibration of an Optical Magnetic Field Me~ure~eht Arr~y, and ~easurement Array Calibrated by ~his ~ethod The invention relate~ to a method ~or temperature calihratlon of an optical mea~urement array for measuring a magnetic field, and to an op~ical mea3urement array for measuring a magnetic field.
OptlcAl me~surement arr~s and me~suring methods for ~eas~ring a magnetic field using the magnetooptical Faraday e~ect are known. The Faraday effect i~ under~tood to mean the rotatlon of the plane of polarization of linearly polarized light as a function of a magnetic field. The angle o~ rotation i~
proportional to the travel integral across the magnetic fleld along the path traversed by the light, with what is known as Ve~det's constant as the proportionality cons~ant. In general, Verdet's constant is dependent on ~aterial, temperature, and w~velength. To me~s~re the magnetlc field, a Faraday sensor device of ~n optlcally transparent material, ~uch as glass, is placed in the m~gnetlc ~ield, The magnetlc field causes a rotation of the plane of polarization of line~rly polarized ligh~, transmit.ted through the Faraday sensor devlce, by a rotary angle that can be evaluated for a measureme~t signal. One ~nown application of such magnetooptical measuring methods and measurement arrays is to measure electrical cur~ehts. To that end, the Faraday sensor device is placed in the viclnlty o~ a curren~ conductor and detects ~he mag~et~c ield generated n the current conductor by a cu~ren~. In ~enera~, the Faraday sensor device surrounds the current conductor, ~o that the measured light circulates around the current conductor in a clo~ed path. In that case, the rotary angle is directly proportional in quantity to the amplitude of the current to ~e me~sured. ~he Fa~aday sensor device may be embodied as a solid glass rlng around the current conductor, or it can ~urround the current conductor with at least one winding, being embodied as a ~easurement winding comprlsing an optical flber ~iber coil).
Advantages of ma~netooptical measurement arrays and mea~uring methoas ovex conventional inductive current converters are the pote~tial separation ~nd the insensitivity to electromagnetic interference. Problems are presented, however, by temperature factors and influences of mechanical bending and vibration in the ~en~or device and the optical transmi~sio~ path~, especially optical fibers, for transmitting the measure~ent llght.
From the Journal of Lightwave Technology, Vol. 12, No. lC, Oct. 1~4, pp. 1882 to l~9o, ~ m~qnetooptical measur1ng syste~
i9 known in which t~o light signa:Ls pass through an opticai series circuit comprlsing a first optical fiber, a fir~t polarizer, a Far~day sensor device, a second polarizer, and a second optical fiber, in opposed directions of circulatlon.
Both light signals, after passing through the optical series circuit, are converted by correspondlng photoelectric converters, each into one elect~ic~l intenslty signal. As the Faraday sensor devlce, a fiber coll comprising a single-mode ~iber with low double refra~tlon ls provided. The polarization axes of the two pol~rlzers form a polarizer angle other than zero degrees with one another; preferably, lt i~
~S~. Llght from a light source i~ split into two li~ht signals, a~d both of these llght signals are fed into the Faraday fl~er coil, each via an optical coupler and an associated tran~mi~sion optical fiber on opposlte ends. From two ele~trical intensity sLgnal~ I1 and I2, whlch correspond to the light intensities of the two llght signals after passing through the serie~ circuit, an intensity-standardlzed ~ 9 ~ û ~ . v v, ~ ~. c i ~ u measurement signal is deri~ed, which corresponds to t~e quotient tI1 - I2)/~I1 + I2) of the difference and the 9um of the two intensity si~nals. Intensity 109~es in the common light path for the two contrary light ~ignal~, and in particular vibratlon-dictated damping in the two optic~l fi~ers, can thus be larqely compensated for. The Journal of Lightwave Technology, Vol. 12, No. 10, Oc~ 1994, pp. 1882 to 1890 ~oes not describe any compensation of temperature influences on the measurement ~ignal. On the cont~a~y, a temperature-insen~itive fi~er coll is used as the sensor device. However, producing such i-iber coils i9 problematlc.
US Patent 5,008,611 dlscloses a magnetooptical mea~urement system, ln which a measurement light ~ignal passes through a serles c~rcuit comprising a first polarizer, a Faraday e~ement, and a second polarizer (analyzer~. To ~ninimize the temperature inf1uence~ re~ulting from the temperature dependency of the linear double refraction in the Faraday element, the angle between the transmission zxis of the first polarizer and the intrinsic double refractlon axis in the Farad~y element is se~ to 10.~~ , and the angle betwee~ the transmission axis of the second polarizer and the intrinsic double refraction axis ln the Faraday element i5 set to 55.3~.
~his setting of the angular values was ascertained empirically and requires previous knowledge of the i~trinsic double refraction axis ~characteristlc directlon) of the Faraday element.
It is now the object of the i~ve~tion to disclose a method for cali~rating an optical measurement array for m~asuring a magnetic field and a cali~rated mea~urement array, ~o that influences of temperat~re ch~nges are practically ellminated.
This ob~ect is attained according to t~e lnventlon wlth the characteristics o~ the claim l or claim 2 and clai~. 6.
3~0 ~~ 8v v, The me~su~eme~t array to be calibrated lncludes a~ optical series circuit comprising a first optical tran3mission path, a ~irst polarizer, a Faraday ~ensor device, a second polarizer, and a second optical transmission path. The polarizatlon axis of the first polarlzer is at a first polarizer angle ~ ~o a predeter~i~ed reference axis. The measurement array of the second polarizer ror~s a second polarizer angle ~ with this ~eference axis. In the method for temperature c~libration of the optlcal measurement array, these two polarizer angles e and ~ are set to opt~al values in terms of the temperature inSensitivity o~ the mea~urement array. First, the sensor device i~ placed in a c~libr~tlng m~gnetic field. At least one light signal is sent through .he optical series circuit of the measuremen~ arr~y, and from the light intensity of the at least one llgh~ signal after passing through the ~eries circuit, a measure~ent sigr.al for the calibrating magnetic fleld ls derived. ~our calibration steps are now performed ln succe~ion:
In a first calibration 9tep, the fir9t polarizer ~ngle ~ is set to a value ~1~ and the second polarizer angle ~ is set to a value ~1, thus essentiall~ meeting the condition~, sin~2Hl - 2~1) = 1, or ~in~2~1 - 2~
and the resultant measureme~t signal is ascertained as a first calibration signal Ml over a predet~rmined temperature range in~l~ding at least two temperature values. In a second callbratlon ~tep, the f_rst polarizer angle ~ is set to a value ~z, and the second polarizer angle ~ is set to a value ~2, thus essentially meet ng the ~ondition, sin~Z~1 - 2~ 1, or sin~2~1 - 2~1) = -1, and d ~3~0 ~~ &~ U
cos~2~2 + 2~2~ = -cos~2~1 ~ 2~1), and the resultant me~surement signal is as~e~tained as a second cali~ratlon ~ignal ~z over the predetermined temperature range.
In a third callbxation step, a correction factor (K) is ascertained such that a cali~ration function MK = ~2 M1 M2~/(M1 + ~2 + K ~M1 ~ ~2))~
w~ich is dependent on the first callbration siynal (M1), the second calibr~tion signal (M2~ ~nd the correction factor (K), is substantlally constant over the predetermined temperat~re range.
Now in the method of claim 1, in a fourth calibration ~tep, the polarizer angles ~ and ~ of the two polari2ers 5, 6 are set such that essentially ~he equa'ions sin~2~ - 2~) - 1, or sin(2~ - 2~) - -1, and cos(Z~ ~ 2~) ~ K Co~((Z~1 + 2~1) are ~et.
In the method of claim ~, conversely, in a fourth calibration ~tep, the polari~er angles ~ and ~ of the two polarizers 5, 6 are set ~uch that the ~esultant measurement signal ~M), for a~
lea3t one temperature value from -~he predetermined temperature range, is sub~tantl~lly equal to the calibration f~nctlon M~.
Both in the method of claim 1 and in ~he method of claim 2, polarizer angles ~ and ~ are o~taine~ with which the measurement array is cali~rated to minimal temperature drift.
The calibration Inethod functions even if the sen~or devlce of the meas~rement array has a nonhomogeneous linear do~ble refraction, and even if an i~trinsic axis of the llnear double refraction in the sen~or device cannot be asce~tained.
d ~S~G CN W'v8v: v h;V,', ;~ 'Cu CA 0225823l l998-l2-l4 Advantageou~ features and further reflneme~ts of the method and the measurement array according to t~e invention are disclosed in the claim~ dependent on claims 1, 2 and 6, respectively.
In an advantageous embodiment, the optlcal series CirCUit of the measurement array ls traversed by two light signals in opposite passage directions from one another.
A~ the measurement ~ignal, a quotient signal of two linear ~unctions of the light intensities of the two light signals, in each ~a~e after they have passed through the optical series circuit, and preferably a signal proportional ~o the ~uotlent of a difference and the sum of the two llght lntenslties, or an effectl~e value of thls slgnal, ls then used as the measurement signal.
In another embodiment, Ihe optical serie~ circuit is traversed by only one light ~ignal. ~he calibrating magnetic field 19 then a substantially constant alternating field, that ioi, a magnetic alternating fleld with a substantlally co~stant ~requency spectrum above a predetermined frequency. ~s the measur~ment ~ignal, a ~ignal i3 u~ed that i~3 proportional to a quotient of an alternating component of the light intensity of the light ~ignal after passing through the series circuit and a direct component o~ this light _ntensity. The alte~natlng component substantially includes the entixe ~re~ency spectrum of ~he calibrating m~gnetic field, while the direct component has no frequencie~ from the frequency spectrum of the calibrating magnetic field, and thus 1~ not dependent on the calibrating maqnetlc fleld. This ~easurement ~ignal is inten~iity 5 tandardized.
For ~urther explanation of the in~ention, reference is made to the drawing, in whlch, i~ each ca~e schem~tl~ally, a ~3 3 ~~ Uv ~ c , vu Fig. 1 shows a measurement array to ~e cali~rated for measuring a magnetic ~ield with a Faraday sensor device;
Fig. 2 shows a measurement arr2y to be cali~rated for measuring a magnetic field with a llght slgn~l; and Fig. 3 shows a measurement array 'or measuring an electrical current wlth t~o liqht slgnals.
Elements that correspond with one another are provided wlth the same ~efere~ce numer~ls.
The measurement array o~ Fig. 1 lnclude~ an optical serie~
circult 1 comprlslng a flrst optical transmi~sion path 4, a fir~t polari~er 5, a sensor device 3, a second pola~lzer ~, and a second optical tran~mission path 7. The sensor device 3 has two optical terminal~ 3~ and 33, such that light inp~t at a terminal 3A or 3~ passes through the sensor device 3 and 1~
output again at the re~pectively other terminal 3B or 3A. The first termlnal 3A of the se~sor device 3 i~ optlcally coupled to one end of the first optical transmisslon path 4 vla the fir~t polarizer ~. The ~econd terminal 3B of the sensor device 3 ls optically coupled to one end of the second optical tran~mlssion path 7 ~1~ the second polarizer 6. An end of the ~irst optical transmission path 4 remote from the fir~t polarizer 5 forms a first terminal lA o~ th~ series circuit 1.
An end o~ the ~econd optical t~ansmlssion path 7 remote ~rom the second polarizer 6 ~orms ~ second terminal lB of the series circuit 1. If measurement light 1~ inp~t at one termlnal lA or lB, ~hen the mea~urement light is transmitted through the series circuit 1 and output from the ~eries circult 1 again at the re~pectiv~ly other terminal lB or lA.
The ~en~or device 3 comprlses at least one material that indicates the magnetooptical Faraday effect, and it can be h c ~J ~; Wv6~ 5~ 86 embodied in a manner khown per se with one or more solid hodies, preferably of slass, or also with at least one optical fiber.
One problem i~ measurin~ a magnetic field with a measurement array according to F1~. 1 i3 presented by temperature lnfluence~ in the sensor de~ice 3. The~e temperature influences induce a linear double refraction ~ as ~ function ~T~ of the temperature T in the sensor device 3, whlch can adulterate the ~easurement of the magnetic fleld. Temperature chan~e~ can also change Verdet's constant and ~h~s the measurement sensitivity.
To keep t~ese temperature influences as sllght a3 po~sible, the measurement array 1~ temperat;lre-calibrated by a calibr~ting method. To th~t end, the sensor device 3 is placed in a callbrating magnetic ield Ho.
In a first embodiment of the callbration method, shown in Fig.
Speciflcation Method f~r Temper~ture Calibration of an Optical Magnetic Field Me~ure~eht Arr~y, and ~easurement Array Calibrated by ~his ~ethod The invention relate~ to a method ~or temperature calihratlon of an optical mea~urement array for measuring a magnetic field, and to an op~ical mea3urement array for measuring a magnetic field.
OptlcAl me~surement arr~s and me~suring methods for ~eas~ring a magnetic field using the magnetooptical Faraday e~ect are known. The Faraday effect i~ under~tood to mean the rotatlon of the plane of polarization of linearly polarized light as a function of a magnetic field. The angle o~ rotation i~
proportional to the travel integral across the magnetic fleld along the path traversed by the light, with what is known as Ve~det's constant as the proportionality cons~ant. In general, Verdet's constant is dependent on ~aterial, temperature, and w~velength. To me~s~re the magnetlc field, a Faraday sensor device of ~n optlcally transparent material, ~uch as glass, is placed in the m~gnetlc ~ield, The magnetlc field causes a rotation of the plane of polarization of line~rly polarized ligh~, transmit.ted through the Faraday sensor devlce, by a rotary angle that can be evaluated for a measureme~t signal. One ~nown application of such magnetooptical measuring methods and measurement arrays is to measure electrical cur~ehts. To that end, the Faraday sensor device is placed in the viclnlty o~ a curren~ conductor and detects ~he mag~et~c ield generated n the current conductor by a cu~ren~. In ~enera~, the Faraday sensor device surrounds the current conductor, ~o that the measured light circulates around the current conductor in a clo~ed path. In that case, the rotary angle is directly proportional in quantity to the amplitude of the current to ~e me~sured. ~he Fa~aday sensor device may be embodied as a solid glass rlng around the current conductor, or it can ~urround the current conductor with at least one winding, being embodied as a ~easurement winding comprlsing an optical flber ~iber coil).
Advantages of ma~netooptical measurement arrays and mea~uring methoas ovex conventional inductive current converters are the pote~tial separation ~nd the insensitivity to electromagnetic interference. Problems are presented, however, by temperature factors and influences of mechanical bending and vibration in the ~en~or device and the optical transmi~sio~ path~, especially optical fibers, for transmitting the measure~ent llght.
From the Journal of Lightwave Technology, Vol. 12, No. lC, Oct. 1~4, pp. 1882 to l~9o, ~ m~qnetooptical measur1ng syste~
i9 known in which t~o light signa:Ls pass through an opticai series circuit comprlsing a first optical fiber, a fir~t polarizer, a Far~day sensor device, a second polarizer, and a second optical fiber, in opposed directions of circulatlon.
Both light signals, after passing through the optical series circuit, are converted by correspondlng photoelectric converters, each into one elect~ic~l intenslty signal. As the Faraday sensor devlce, a fiber coll comprising a single-mode ~iber with low double refra~tlon ls provided. The polarization axes of the two pol~rlzers form a polarizer angle other than zero degrees with one another; preferably, lt i~
~S~. Llght from a light source i~ split into two li~ht signals, a~d both of these llght signals are fed into the Faraday fl~er coil, each via an optical coupler and an associated tran~mi~sion optical fiber on opposlte ends. From two ele~trical intensity sLgnal~ I1 and I2, whlch correspond to the light intensities of the two llght signals after passing through the serie~ circuit, an intensity-standardlzed ~ 9 ~ û ~ . v v, ~ ~. c i ~ u measurement signal is deri~ed, which corresponds to t~e quotient tI1 - I2)/~I1 + I2) of the difference and the 9um of the two intensity si~nals. Intensity 109~es in the common light path for the two contrary light ~ignal~, and in particular vibratlon-dictated damping in the two optic~l fi~ers, can thus be larqely compensated for. The Journal of Lightwave Technology, Vol. 12, No. 10, Oc~ 1994, pp. 1882 to 1890 ~oes not describe any compensation of temperature influences on the measurement ~ignal. On the cont~a~y, a temperature-insen~itive fi~er coll is used as the sensor device. However, producing such i-iber coils i9 problematlc.
US Patent 5,008,611 dlscloses a magnetooptical mea~urement system, ln which a measurement light ~ignal passes through a serles c~rcuit comprising a first polarizer, a Faraday e~ement, and a second polarizer (analyzer~. To ~ninimize the temperature inf1uence~ re~ulting from the temperature dependency of the linear double refraction in the Faraday element, the angle between the transmission zxis of the first polarizer and the intrinsic double refractlon axis in the Farad~y element is se~ to 10.~~ , and the angle betwee~ the transmission axis of the second polarizer and the intrinsic double refraction axis ln the Faraday element i5 set to 55.3~.
~his setting of the angular values was ascertained empirically and requires previous knowledge of the i~trinsic double refraction axis ~characteristlc directlon) of the Faraday element.
It is now the object of the i~ve~tion to disclose a method for cali~rating an optical measurement array for m~asuring a magnetic field and a cali~rated mea~urement array, ~o that influences of temperat~re ch~nges are practically ellminated.
This ob~ect is attained according to t~e lnventlon wlth the characteristics o~ the claim l or claim 2 and clai~. 6.
3~0 ~~ 8v v, The me~su~eme~t array to be calibrated lncludes a~ optical series circuit comprising a first optical tran3mission path, a ~irst polarizer, a Faraday ~ensor device, a second polarizer, and a second optical transmission path. The polarizatlon axis of the first polarlzer is at a first polarizer angle ~ ~o a predeter~i~ed reference axis. The measurement array of the second polarizer ror~s a second polarizer angle ~ with this ~eference axis. In the method for temperature c~libration of the optlcal measurement array, these two polarizer angles e and ~ are set to opt~al values in terms of the temperature inSensitivity o~ the mea~urement array. First, the sensor device i~ placed in a c~libr~tlng m~gnetic field. At least one light signal is sent through .he optical series circuit of the measuremen~ arr~y, and from the light intensity of the at least one llgh~ signal after passing through the ~eries circuit, a measure~ent sigr.al for the calibrating magnetic fleld ls derived. ~our calibration steps are now performed ln succe~ion:
In a first calibration 9tep, the fir9t polarizer ~ngle ~ is set to a value ~1~ and the second polarizer angle ~ is set to a value ~1, thus essentiall~ meeting the condition~, sin~2Hl - 2~1) = 1, or ~in~2~1 - 2~
and the resultant measureme~t signal is ascertained as a first calibration signal Ml over a predet~rmined temperature range in~l~ding at least two temperature values. In a second callbratlon ~tep, the f_rst polarizer angle ~ is set to a value ~z, and the second polarizer angle ~ is set to a value ~2, thus essentially meet ng the ~ondition, sin~Z~1 - 2~ 1, or sin~2~1 - 2~1) = -1, and d ~3~0 ~~ &~ U
cos~2~2 + 2~2~ = -cos~2~1 ~ 2~1), and the resultant me~surement signal is as~e~tained as a second cali~ratlon ~ignal ~z over the predetermined temperature range.
In a third callbxation step, a correction factor (K) is ascertained such that a cali~ration function MK = ~2 M1 M2~/(M1 + ~2 + K ~M1 ~ ~2))~
w~ich is dependent on the first callbration siynal (M1), the second calibr~tion signal (M2~ ~nd the correction factor (K), is substantlally constant over the predetermined temperat~re range.
Now in the method of claim 1, in a fourth calibration ~tep, the polarizer angles ~ and ~ of the two polari2ers 5, 6 are set such that essentially ~he equa'ions sin~2~ - 2~) - 1, or sin(2~ - 2~) - -1, and cos(Z~ ~ 2~) ~ K Co~((Z~1 + 2~1) are ~et.
In the method of claim ~, conversely, in a fourth calibration ~tep, the polari~er angles ~ and ~ of the two polarizers 5, 6 are set ~uch that the ~esultant measurement signal ~M), for a~
lea3t one temperature value from -~he predetermined temperature range, is sub~tantl~lly equal to the calibration f~nctlon M~.
Both in the method of claim 1 and in ~he method of claim 2, polarizer angles ~ and ~ are o~taine~ with which the measurement array is cali~rated to minimal temperature drift.
The calibration Inethod functions even if the sen~or devlce of the meas~rement array has a nonhomogeneous linear do~ble refraction, and even if an i~trinsic axis of the llnear double refraction in the sen~or device cannot be asce~tained.
d ~S~G CN W'v8v: v h;V,', ;~ 'Cu CA 0225823l l998-l2-l4 Advantageou~ features and further reflneme~ts of the method and the measurement array according to t~e invention are disclosed in the claim~ dependent on claims 1, 2 and 6, respectively.
In an advantageous embodiment, the optlcal series CirCUit of the measurement array ls traversed by two light signals in opposite passage directions from one another.
A~ the measurement ~ignal, a quotient signal of two linear ~unctions of the light intensities of the two light signals, in each ~a~e after they have passed through the optical series circuit, and preferably a signal proportional ~o the ~uotlent of a difference and the sum of the two llght lntenslties, or an effectl~e value of thls slgnal, ls then used as the measurement signal.
In another embodiment, Ihe optical serie~ circuit is traversed by only one light ~ignal. ~he calibrating magnetic field 19 then a substantially constant alternating field, that ioi, a magnetic alternating fleld with a substantlally co~stant ~requency spectrum above a predetermined frequency. ~s the measur~ment ~ignal, a ~ignal i3 u~ed that i~3 proportional to a quotient of an alternating component of the light intensity of the light ~ignal after passing through the series circuit and a direct component o~ this light _ntensity. The alte~natlng component substantially includes the entixe ~re~ency spectrum of ~he calibrating m~gnetic field, while the direct component has no frequencie~ from the frequency spectrum of the calibrating magnetic field, and thus 1~ not dependent on the calibrating maqnetlc fleld. This ~easurement ~ignal is inten~iity 5 tandardized.
For ~urther explanation of the in~ention, reference is made to the drawing, in whlch, i~ each ca~e schem~tl~ally, a ~3 3 ~~ Uv ~ c , vu Fig. 1 shows a measurement array to ~e cali~rated for measuring a magnetic ~ield with a Faraday sensor device;
Fig. 2 shows a measurement arr2y to be cali~rated for measuring a magnetic field with a llght slgn~l; and Fig. 3 shows a measurement array 'or measuring an electrical current wlth t~o liqht slgnals.
Elements that correspond with one another are provided wlth the same ~efere~ce numer~ls.
The measurement array o~ Fig. 1 lnclude~ an optical serie~
circult 1 comprlslng a flrst optical transmi~sion path 4, a fir~t polari~er 5, a sensor device 3, a second pola~lzer ~, and a second optical tran~mission path 7. The sensor device 3 has two optical terminal~ 3~ and 33, such that light inp~t at a terminal 3A or 3~ passes through the sensor device 3 and 1~
output again at the re~pectively other terminal 3B or 3A. The first termlnal 3A of the se~sor device 3 i~ optlcally coupled to one end of the first optical transmisslon path 4 vla the fir~t polarizer ~. The ~econd terminal 3B of the sensor device 3 ls optically coupled to one end of the second optical tran~mlssion path 7 ~1~ the second polarizer 6. An end of the ~irst optical transmission path 4 remote from the fir~t polarizer 5 forms a first terminal lA o~ th~ series circuit 1.
An end o~ the ~econd optical t~ansmlssion path 7 remote ~rom the second polarizer 6 ~orms ~ second terminal lB of the series circuit 1. If measurement light 1~ inp~t at one termlnal lA or lB, ~hen the mea~urement light is transmitted through the series circuit 1 and output from the ~eries circult 1 again at the re~pectiv~ly other terminal lB or lA.
The ~en~or device 3 comprlses at least one material that indicates the magnetooptical Faraday effect, and it can be h c ~J ~; Wv6~ 5~ 86 embodied in a manner khown per se with one or more solid hodies, preferably of slass, or also with at least one optical fiber.
One problem i~ measurin~ a magnetic field with a measurement array according to F1~. 1 i3 presented by temperature lnfluence~ in the sensor de~ice 3. The~e temperature influences induce a linear double refraction ~ as ~ function ~T~ of the temperature T in the sensor device 3, whlch can adulterate the ~easurement of the magnetic fleld. Temperature chan~e~ can also change Verdet's constant and ~h~s the measurement sensitivity.
To keep t~ese temperature influences as sllght a3 po~sible, the measurement array 1~ temperat;lre-calibrated by a calibr~ting method. To th~t end, the sensor device 3 is placed in a callbrating magnetic ield Ho.
In a first embodiment of the callbration method, shown in Fig.
2, only ~ sinqle light signal L is passed through the optical series circuit 1. To that end, the terminal lA, for instance, of the series clrcuit 1 i~ optic~lly coupled with a li~ht source. As the calibrating magnetic field Ho~ a magnetic alternating field with a ~ubstar,t:-ally con3tant frequency ~pectrum above a predetermined frequency is used. After pa33ing through the serle~ circuit 1, a measurement signal M
i~3 derived froIrl the light signal L by evaluation means 3~; the measurement si~nal is proportional to a quotient of an alternatln~ component of the light inten~ity of the light sig~al after passing through the ~eries clrouit and a direct component of this llght intensi~y~ The alternatlng component e~entiall~ includes the entire fre~uency spectrum of the calibrating ma~netlc field, while the direct componert has no frequencles from the frequency ~pectrum o~ the calib~atin~
magnetic fie~d, or in other words does n~t depend on the calibrating magne~ic field. To _hat end, with a photodetector v d cg-J ~ 'C, ~6c, ~ 'ù
~1 associated with the terminal lB of the series circuit 1, the light signal L is converted into an electric~l i~tensity signal I as a measure of the light intensity of the light signal ~. From this electrical intensity ~ignal I, an alternating signal component A, as a measure for the alterna~lng component of the light intensity, ls ~ormed with a high-pass filter 32, and a direct signal component D, as a measure ~or the direct component o~ the light inten~ity, i~
formed with a low- pass filter 33. A divider 34 fcrm~ the ~uotient A/D of the alternating si~al component A and the di~ect ~ignal component D of the intensity signal I, ~orming the measurement ~ignal M. The measurement signal M thu~
formed is intensity-sta~dardized but 9 ~till temperature-dependent.
In another embodiment of ~he cali~ratlrg ~ethod, two light signals are sent in opposite directions through the series circuit 1 and ~ubsequently su~ected to sign~l e~luation. As the measurement signal, a quotient slgn~l o~ two linear functlons of the light intensities of the two light ~lgna~ A, in e~ch o~se after passing through the optical series circuit, and preferably a signal proportional to the quotient of a difference and the sum of the two ligh~ intensltie~, o~ an effective value of ~his signal, i~ determlned. This mea~urement ~ignal is also intensity-standardi~ed, but is still temperature-dependent. In this embodiment, a magnetic field that i~ cons~ant over time is prefera~ly used as the calibrating magnetic ~ield Ho. An advan~ageous embodiment of a measurement array for ~his kind of callbratlng method of two light ~ignal~ is shown ln Fig. 3.
The measure~ent array of Fig. 3 includes means f~r txansmitting two l~ght signals L1' and ~2~ through the serie~
circuit 1, pas~in~ ~hrough i~ in opposite di~ections, and evaluation means 20 for e~aluating the light signals L1 and L2 ~fter the~ pa~s through the series circuit 1. The ~e~ns for u ~ ~ ~'9CC ' N ~ , hvû
transmitting the two light 9ignals L1' and L2' include a light source 1~ and three optical couplers 11, ~2 and 1~. The other end~, remote from the 3en90r de~ice 3, of the first transmission path 4 ~terminal lA of the ~eries circuit 1) ls optically co~ected via the optical coupler 12 bo~h with the further optical coup}er 11 and with evaluation means 20. The other end of the ~econd ~ransmission path 7 remote from the sensor device 3 (that is, the terminal lB of the series clrcuit 1) is also optically connected via the optical coupler 13 with both the optic~l coupler 11 and the evaluation means 20. The optical coupler 11 ls optically connected to the light source 10, and it splits ~he light L of the light souxce 10 into two light signals L1' and L2', which are delivered to the couplers 12 a~d 1~, respectively, and then are lnput to the first and second transmission path 4 and 7, respectively.
Both light signais Ll' and L2' ~ass through the optlcal ser_es circult 1 comprislng t~e first transmission path 4, the first polarizer 5, the sensor device 3, the second polarizer 6, and the second transmission path 7 in passage direction~ oppo3ite one another and are output from the serles circuit again, now as light signals designated L1 and ~2, respectively.
The couplers 11, 12 and 13 may at least partly be replaced ~y opti~al beam ~plitters. Furthe~more, instead of the coupler 11 and one light source 10, two light sources may be provlded, which each transmit one light signal L1' and L2', respectively. The means for transmittin~ two light signals L1 and L2 through the series circuit, traversing it in oppo~ite directions, may furthermore ~e e~odied ~y two photoelectric converter~ operated ln alternation as transmitters and recelver~, which ar~ then al~o provided in order to conver~
the li~ht slgnals L1 and L2, after passing through the ser es circuit, into e~ectrical lntensity signals.
The first light signal L1', after passing through the first transmission path 4, is linearly polarlzed by the first ~ 1 C--~ ~ c ~9~0 CN ~'vJv ~
polariz~r 5 and i~ fed, as a now linearly polarized light signal L1', into the sens~r devi~e 3 at the termlnal 3A. 0~
passlng through the sensor de~lce 3, the pol~rization plane of the llnearly polarized first light signal L1' is rotated by a Faraday measurement angle that is dependent on the calibrati~g magnetic field Ho. ~he first light signal L1', rotated about the measurement angle in its polarization plane, is now delivered to the second polarizer 6. The second polarizer 6 allows only the component of the oncoming first light signal L1' that is projected or.to its po:Larization axis to pass through, and thus has the func~ion of a polarization analyzer for the first light signal L1'. The component of the¦-f~ t light signal L1' transmitted ~y the second polarizer 6 is now designated Ll ~n~ ls trans~itted _o the evaluation means 20 via the second transmission path '7 and the coupler 13.
The second light signal L2' first passes through the second transmlssion path 7 and ls then linearly polarlzed by the first polarizer 5. The linearly polarized second lig~t signal I~2' i~ now input at the sensor device ~ at the terminal 3A.
On passlng through ~he sen~or device 3, the pol~rlzatlon plane of the linearly polarized second,light signal L2' ls rotated by a Faraday measurement angle dependent on the calibratlng magnetic field Ho~ which angle has the opposite sign, because of the non~eclprocal property of the ~araday effect, an~ the same quantity as the fi~t light signal Ll'. The second light sign~l L2', ro~ated in its polarization plane a~ou~ the measurement angle, is now delivered to the se~ond polarizer 6.
The second polarizer 6 allows only the component of the oncoming second light sign~l L~ that is projected on its polarization axi~ to pass throu~h, and thus act~ as a polarization analyzer of the second light signal ~'. The component of the second light signal L2' t~an~mitted by the second polarizer 6 1s r.ow designated ~2 and is transmitted ~o the evaluation means 20 via the first tran~mission path 4 and b~_Sg~l~r~ 2.
~, a first light signal ~1' 'ransmit~ed by the se~or.d polarizer i9 desig~ated L1 and is ~ransmitted to Ihe evcluatlon d~v'ce 20 through the second trarlsmission path 7 and the coupler 13 5 The second llght slg~al L2' first passe~ through the sec~~d tra~.s~'s~ion pa-~, 7 ar.G is then ;inearly polarized by the seccnd polarizer 6. ~he linearly polarized ~econd ligh;
slgn2l L2' i~3 inp.lt t~ tl~e sensor device 3 at the ter~r,iria ~B.
Upon passlng ~hro~gh ~he senso~ device 3, the polarization lo plane Oc the linearly polar zed second light ~ignal ~2~ is rotated by ~ Faraday -.,easure~,ent angle dependent or~ the ca'ibrating magne~ic lie_c rO. ~he an~e ~,a~ the oppcsl-e sign, ~ecause o~ .~.e ~c~-re~ p-ocal proper~y of the aradcy effect, and haq the same quantity as ~he fi~t lign~ signa Ll'. The ~econd ;i~.t slgIlal L2', wh;ch i9 rota'ed f-i its po_axiz~ion plane abo~t ~.e ~easureme~ angle, ls ther~
de i~ered to the f~st ~lar.zer 5. The 'i~st po:arizer 5 a~lows only the co~.ponen_ o~ the oncoming second ;ig~.t slc-nal L2 that i~ projected on its polariz~tion axis to pass ~hrou~,h, 2C and thu9 acts ac a polarization anal yzer of the ~eccn~ llFh~
signai L2' . The cc~ oner-t O r the second light slgna ~2' ~h_c;~ ansmi~ed by t'ne f'rst po'a~izer 5 is designated L2 and is ~ransmltted t:~roug;q tne firs~ transm~lon pa~h 4 an~
the co~le~ :2 ,o ~he e~a:~a~ o~ devlce ~0.
-lla-The light intensities I1' and I2' of the two light signal3 Ll' and L2', before being input into the series circuit, are generally set to a fixedly predetermined ratio to one another.
P~eferably, both light inten~ities are the same; that is, I1' = I2'. In the embodiments shown, the coupler 11 then splits the light L of the light source 10 into two equal parts wlth a coupling ratio of 50~:50%.
Upon traversing the two transmis5ion paths 4 and 7, both light signal~ L1' and ~1 an~ L2' and L2, respectivel~, ~ndergo the same change~ in intensity, which can be ~aused particularly by damping losses resulting from mechanical vi~ration. These changes in inten~ity are essentia:L~y expressed a~ damping factors in the light intenslties I1 and I2. The real damping ~actor, whlch is ~enerally time-dependent of an optical transmission path is define~ zs the ratio of the light intehSity of light arriving at one end of the transmis~ior path to the input light intensity as the light is input at the other end o~ the transmission path. The damping fac~ors OL
the transmlssion paths 4 ~nd 7 are now eliminated, in that the evaluation ~eans 2~ derive a quotient signal, in genexal in the for~ of a measurement signal M for the calibrating ma~neti~ ~ield Ho, which quotient signal takes the form M (a ~ I1 + b - I2 + c)/~d I1 ~ e ~ I2 + f) (1) from t~o llnear functions (a Il + b I2 + c) and ~d ~ I1 + e -I2 + f) of the two light intensities I1 and I2 wlth the real coefflcient~ a, b, c, d, e and f. At least elther the coefficient~ a and e, or the coefficients b and d, are othe~
than zero.
This meas~rement sign~l M is practically independen~ of changes in lntensity, caused in particuldr by vibration in the transmission paths 4 and 7. ~hu~ in all the embodi~ents, even d ~gc~ c~
.
~he simple, comparatively inexpensive telecommunications optical fibers (multimode fibers) can be used as the t~ansmis~ion paths 4 an~ 7, since the relatively high damplng and vibration sen~itivity of these fibers a~e compensated for in the measurement signal M. However, other optical fi~ers or free-beam arrays can also ~e used.
The coefficlents a, ~, c, d, e and f of the linear f~nctions in the numerator and denominator of equatlon (1) can ln particular be adapted to different input intensities of the two light signals upon ~e ng lnput into the serie~ circuit.
The coefficients d, e and ' of the linear function d I1 + e I2 + f in the denomlna~or of the quotient in equation (l) a-e prefe~ably set such that the linear function d ~ I1 + e ~ I2 +
f is practically constan~ and is t:hus independent o~ the ma~netic field Ho.
Particularly, when the input ir.tensities I1' and I2' of both liqht sign~ls L-1' and L2' are approximately the ~ame, lt is pos~ible in the advantageous e.~bodiment shown in Fi~. 3 also to use the quotient M = (Il - I2)/~I1 + I2~
of a di~ference I1 ~ I2 ~o~ I2 ~ and the sum I1 ~ I2 of the two light intenslties -1 and I2 after passing through the series circuit as the ~eas~rement signal M. In the embodiment shown, the e~aluatlon ~e~ns 20 for derivin~ the measurement signal M, have two photoelectric converters 21 and 22, a sub~ractor 23, an adder 24, an~ a dlvlder 25. The first converter 21 is optically connec~ed to the couple~ 13 and convert~ the first li~ht s_gna_ L1, a ter it has passed through the series circult, lr.to a first electrical intens~ty signal S1, whose signal irten~lty corresponds to the light intensity I1 of the first light signal L1. The second converter 22 is optically conr.ected to the coupler 12 and . ~ 89~0 ~N l'~ 0, 8vv. ~ a converts the second light 5ignal L2, after it h~s p~ssed through the serie~ circuit, into a second electrical intensity slgnal SZ as a measure of the light intenslty I2 of the second light signal L2. The two inten~ity signals S1 and 52 are e~c~
delivered to one input of the subtractor 23 and of the adder 24. T~e difference signal S1 - S2 ~or S2 - S1~ at the output of the subtractor 23 and the su~mation signal S1 I S2 at the output of the adde~ 24 are each delivered to one input o~ the divider ~S. The o~tput signal of the divider ~S1 - S2)/~S1 ~
s2~ is utilized as the measurement 3ignal M and is switched to one o~tput o~ the evaluatlcn mean9 20. This embodiment has the advantage that analog components, which a~ a rule are faste~, as digital component~.
In an embodiment not shown, the two electrical lntensity signals can also first be digitized, however, with the aid of an analog/digital converter, ~d then the ~itized signals can then be furtner processed by a microprocessor OL a digital signal processor.
~y adapting the coefficients a, b, c, d, e and f ln the general mea~urement ~ignal M = (a ~ I1 + ~ I2 + c)/(d ~ e ~ I2 + f), it is posslble in particular to compen~ate for different ~en~itivities o~ the two photoelectric converters 21 and 22.
The measurement array of Fig. 3 to be calibrated i~ preferably intended for mea~uring an electrlcal current I i~ at least one current conductor 2. The sensor device 3 then de~ects the magnetic f~ield generated induc_iv~3ly by this current I. The sensor device 3 pre~er~bly s~rr~nd~ the c~rre~t co~ductor ~, ~o that both light ~ignal~ L1' and L2' carry the current I in a practically closed light path. ~n thls case, the measurement angle is directly propo~tlona~ to the electrlcal current I. The sen~or device 3 lnay be embodied a~ a solid glass ring with ir.ner re~leot-ve ~aces that deflect the light :4 , d ~9~0 CN Ju~":0~ ~36i Til~5 51gnals Ll' sn~ L2', or may be embodied in some other known ~ay. The constant ~alibrating magnetic ~ield ~ can be set by adiusting a constant ~urrent I in the current conductor 2.
The temperature dependency of the measurement signal M is now essentially eliminated by means of the calibration method for temperature compensat~on descrlbed below. ~he calibration ls done by mean~ of the optimal setti.ng o~ the polarizer angles of the two polarizers 5 and k.
Figs. 4-6 show three po3sible calibration steps ~or settlng these optlmal polarizer angles of the polarizer~ 5 and 6. In Figs. 4- 6, a polarization axis (transmission axis, characteristic axis, intrinsic ax-s) of the ~irst polarizer 5 i9 desi~na~ed Pl, and a polarizatLon axi~ of the secorld polarizer 6 ls designated P2. ~he Dolarization axes Pl and P2 are located in a plane oriented perpendlcular to the light propagation direction of the l~.gh; passing ~hrough the polarizer~ 5 and 6. A reference axis, whlch can be predetermined arbitr~rily and is al50 loc~ted in this plane, i~ desi~nated R. The polarization axis Pl of the first polarizer 5 forms d first polarizer angle ~ with the predetermined ~eference ~xis R, while the polar~za~ion axis F~
of the second polarizer 6 is oriented ~t a ~econd polarizer angle ~ to the reference axi~ R.
In a first calibration step, the polarizer angle3 H and ~ of the two polarizers 5 and 6, re~pectively, ar~ set s~ch that maximUm ~mall-slgnal ~ensitlYity is achieved. To that end, the first polarizer angle H is set to a .irst calibration val~e ~ ~nd the second polarizer angle ~ is set to a first calibration value ~1, e~sentially in accor~ance with the equation sin(Z~l - 2~ 1 tla) ~1 c ~9~ o~ C~ 86c or sin(2~1 - 2~ 1 (lb).
With the thus-set polarizer angles ~ and ~ , the resultant measurement signal M i~ plotted as a first cali~ration signal M1 over a predetermlned tempe~ture r~nge, including at lea3t two temperature values, and is stored in memory. The temperature range is selected in accordance with the expected temperatures of use o~ ~he me~s~rement arr~y.
~ne or the other of the condltions (la~ or (lb) is met in particular i~ ~he polarization axes Pl and P2 fo~ an ~ngle of _ 45~ (i ~f4) with one another.
Fig. 4 shows an exemplary embodiment in which the polarizer angles ~ and ~ are set to calibration values ~1 and ~1~
respectively, that meet condition (la). The polariz~tlon axls P2 of the second polarizer 6 is inclined relatlve to the polarization axis P1 o~ the first polarizer 5 by the angle ~1 -~1 - +45~. Posltive angles here and below indicate the mathematically positive direction o~ revolution ~counterclockwi~e).
In a second calibration ~tep, the fir~t polarizer angle ~ i~
set to a cali~ration value ~2~ and the second polarizer angle is set to a calibration value ~, so that essentially the con~ition ~in~2~2 ~ 2~z~ 2 or sint2~z - 2~2~ 2b~
on the one h~nd, and at the same time the condition cost2~2 + 2~2) - -COS~(2~1 + 2~1~ (3) L, d ~9(~ C ~ ~66 ~, ~C"
on the other are met. With the thu~-set polarizer angles ~ -~2 and -- rl2~ the resultant measurement signal ~) is ascertained as a second cali~ration ~lgnal Mz over the predetermined temperature xange, and is llkewi3e stored in me~ory. ~o set the polarizer angles ~ and ~ to thelr second calibratlon values ~3z and ~2, it is possible for in~tance compared with the ~irst calibration values ~1 and ~1 to rotate the pol~rization axls P1 or P2 of one of the two polari~ers 5 and 6 farther by ~0~, or to rotate bo~h polarization axes ~1 and P2 farther, each by 45~.
Fig. 5 shows an e~peci~lly easily set embodiment of the second calihration s~ep. In compari~on to the setting in Fig. 4, the polarization axis P1 of the first polarize~ ~ ls unchan~ed;
that is, (31 ~ ~2, a~d only the second polarizer 6 i~ rotated by -9o~ relative to _he reference axis ~; that is, Tl2 = ~1~ + 90~-The angle formed by ~he two polarization axes P1 and P2 i9 then ~32 -~2 = -45~.
The calibration signals M1 a~d M2 obtained from the first calibration ~tep and the ~econd calibration ~tep are functions M1(T) a~d Mz(T), xespectively, of the temperature T over the predetermined t~mperature range and can be analytically de~cribed ln a good approximation a~ follow~:
M~ (~) =1+cos(2~l+~l)f2(T) M (~)= f'( ) = f'~ ) (5 1 + cos(2~ + 2r12 ) f2 (T) l-cos(2~l+~)f2 (T) ' v v u u N ~'V~ 7 ~ 6 6, , Solving the two equations (4) and ~5) for fl(T) and cos(2~1 +
2~) fz~T), and inserting a real correc~io~ factor K, leads to the equation for the calibration function:
M,~ (~) = M Jr A~ + K(M, -M2 ) ( 6 ) The correction factor K is preferably determined in a thlrd calibration step, by means of a simple numerical process and with the aid o~ a digltal signal processor or a mic~opxocessor, su~h that the temperature drift ~f the associated calibration function ~K~T) ~ecomes minimal. This means that the calibration function ~K = (2M1M2~/(M1-+ M~ + K -(M1 - M2)), which is dependent on the first calibration signal M~, the second calibration sign~l M2, and the correction f~ctor K, is essentially constant over the predetermined ~empera.u~e range.
If the predetermined temperature range (calibration range) includes only two temperature values T" and Tb~ then to that end, with the aid of the corresponding calibration ~ignal value~ M1(TA) and M2 (Ta~ ~ as well as Ml(Tb~ and M2(Tb~, the equation M~(Ta) -- MK~Tb) is simply solved for the correction factor K.
Conversely, if the predetermined temperature range includes more than two temperature measurement points, then y = f ~T~ =
2~2/(M2 - Ml) can be plotted in a graph relative to x = cos(2 + 2~)fz~T) = (M1 + M2)~(M2 - M1). Thl~ gra~h is fitted llnearly with the function Y~X) - MK(1 ~ KX) (8) 6~ d ~9'10 CN Wb~ 9. ~66. , i J~
with the fitting parametexs M~ and K.
In a four~h calibration step, the polarizer angles ~ and ~ of the two polari~ers 5 and 6 ~re now set ln accordance with Fi~.
6 in such a way that the resultant meas~rement ~ignal M has minimal ~emperatUre drift.
In a flrst embodi~ent of this fourth ca~i~ration step, the polarizer angles O and ~ of the two polarizers 5, 6 are adjusted such t~at es~enti~lly the equation~
~in~2~ - 2~) = l (9a~
or sin(2~ 2~ 9b) and co~(2~ + ~ cOs((2~1 i 2 l) (l~).
To that end, by way of example, t~e polarization axes Pl and P2 c~n be rotated, comp~red to the ~ettlng in Flg. 5, in the same direction by the same angle while maintaining the same angle of - 45~ (condition (9~ formed ~y the polarizatlon axes Pl and P2, until such time as condition (lO) i~ met. In a second embodlment of .he fourth calibration step, the polarizer angles ~ ~nd ~ of the two polarizers 5, 6 are adj~sted such that the resultant measuremen~ signal M, ~or at least one temperatur~ value TD from the predetermined temperature range, is substantially equal to the calibrat~on functlon M~, and accordingly:
M(TO) ~ M~(TO) (11).
In both the first em~odiment ln accordance with equa~ions ~9a), (9b) and ~lO), ~nd in th~ second embodiment in accordance wi~h equation (ll~ of the ~ourth calibratlon step, 0~ d ~9S0 ~N Wb~t: C, X~, ii, ~3u ., , . . ~ _ the two polarizer angles ~ and rl of the two polarizers 5 ~nd 6, re~pectively, are adjusted optlmally for ~inim~l temperature dependency o~ the measurement slgnal M in the predetermined ~emperature range.
Instead of the measurement signal M itself, in all the embodiments it is al90 possible to u3e the effective value of the measurement signai ~ for the temperature calibration, if alternatlng magnetic fielà9 are to ~e measured, One fundamental advantage of temperature compensatlon by setting the polarize~ angles ~ ~nd ~ i~ the high bandwidth upon measuring magnetic flelds H or elec~rical currents I.
The frequency spectrum of the magne~ic fields H or electrical currents I to be measured is not in fact limited in principle by the provisions made for temperature compensatlon.
i~ d v9~ ~~j t~'7: Ji ~iV'i -j, '
i~3 derived froIrl the light signal L by evaluation means 3~; the measurement si~nal is proportional to a quotient of an alternatln~ component of the light inten~ity of the light sig~al after passing through the ~eries clrouit and a direct component of this llght intensi~y~ The alternatlng component e~entiall~ includes the entire fre~uency spectrum of the calibrating ma~netlc field, while the direct componert has no frequencles from the frequency ~pectrum o~ the calib~atin~
magnetic fie~d, or in other words does n~t depend on the calibrating magne~ic field. To _hat end, with a photodetector v d cg-J ~ 'C, ~6c, ~ 'ù
~1 associated with the terminal lB of the series circuit 1, the light signal L is converted into an electric~l i~tensity signal I as a measure of the light intensity of the light signal ~. From this electrical intensity ~ignal I, an alternating signal component A, as a measure for the alterna~lng component of the light intensity, ls ~ormed with a high-pass filter 32, and a direct signal component D, as a measure ~or the direct component o~ the light inten~ity, i~
formed with a low- pass filter 33. A divider 34 fcrm~ the ~uotient A/D of the alternating si~al component A and the di~ect ~ignal component D of the intensity signal I, ~orming the measurement ~ignal M. The measurement signal M thu~
formed is intensity-sta~dardized but 9 ~till temperature-dependent.
In another embodiment of ~he cali~ratlrg ~ethod, two light signals are sent in opposite directions through the series circuit 1 and ~ubsequently su~ected to sign~l e~luation. As the measurement signal, a quotient slgn~l o~ two linear functlons of the light intensities of the two light ~lgna~ A, in e~ch o~se after passing through the optical series circuit, and preferably a signal proportional to the quotient of a difference and the sum of the two ligh~ intensltie~, o~ an effective value of ~his signal, i~ determlned. This mea~urement ~ignal is also intensity-standardi~ed, but is still temperature-dependent. In this embodiment, a magnetic field that i~ cons~ant over time is prefera~ly used as the calibrating magnetic ~ield Ho. An advan~ageous embodiment of a measurement array for ~his kind of callbratlng method of two light ~ignal~ is shown ln Fig. 3.
The measure~ent array of Fig. 3 includes means f~r txansmitting two l~ght signals L1' and ~2~ through the serie~
circuit 1, pas~in~ ~hrough i~ in opposite di~ections, and evaluation means 20 for e~aluating the light signals L1 and L2 ~fter the~ pa~s through the series circuit 1. The ~e~ns for u ~ ~ ~'9CC ' N ~ , hvû
transmitting the two light 9ignals L1' and L2' include a light source 1~ and three optical couplers 11, ~2 and 1~. The other end~, remote from the 3en90r de~ice 3, of the first transmission path 4 ~terminal lA of the ~eries circuit 1) ls optically co~ected via the optical coupler 12 bo~h with the further optical coup}er 11 and with evaluation means 20. The other end of the ~econd ~ransmission path 7 remote from the sensor device 3 (that is, the terminal lB of the series clrcuit 1) is also optically connected via the optical coupler 13 with both the optic~l coupler 11 and the evaluation means 20. The optical coupler 11 ls optically connected to the light source 10, and it splits ~he light L of the light souxce 10 into two light signals L1' and L2', which are delivered to the couplers 12 a~d 1~, respectively, and then are lnput to the first and second transmission path 4 and 7, respectively.
Both light signais Ll' and L2' ~ass through the optlcal ser_es circult 1 comprislng t~e first transmission path 4, the first polarizer 5, the sensor device 3, the second polarizer 6, and the second transmission path 7 in passage direction~ oppo3ite one another and are output from the serles circuit again, now as light signals designated L1 and ~2, respectively.
The couplers 11, 12 and 13 may at least partly be replaced ~y opti~al beam ~plitters. Furthe~more, instead of the coupler 11 and one light source 10, two light sources may be provlded, which each transmit one light signal L1' and L2', respectively. The means for transmittin~ two light signals L1 and L2 through the series circuit, traversing it in oppo~ite directions, may furthermore ~e e~odied ~y two photoelectric converter~ operated ln alternation as transmitters and recelver~, which ar~ then al~o provided in order to conver~
the li~ht slgnals L1 and L2, after passing through the ser es circuit, into e~ectrical lntensity signals.
The first light signal L1', after passing through the first transmission path 4, is linearly polarlzed by the first ~ 1 C--~ ~ c ~9~0 CN ~'vJv ~
polariz~r 5 and i~ fed, as a now linearly polarized light signal L1', into the sens~r devi~e 3 at the termlnal 3A. 0~
passlng through the sensor de~lce 3, the pol~rization plane of the llnearly polarized first light signal L1' is rotated by a Faraday measurement angle that is dependent on the calibrati~g magnetic field Ho. ~he first light signal L1', rotated about the measurement angle in its polarization plane, is now delivered to the second polarizer 6. The second polarizer 6 allows only the component of the oncoming first light signal L1' that is projected or.to its po:Larization axis to pass through, and thus has the func~ion of a polarization analyzer for the first light signal L1'. The component of the¦-f~ t light signal L1' transmitted ~y the second polarizer 6 is now designated Ll ~n~ ls trans~itted _o the evaluation means 20 via the second transmission path '7 and the coupler 13.
The second light signal L2' first passes through the second transmlssion path 7 and ls then linearly polarlzed by the first polarizer 5. The linearly polarized second lig~t signal I~2' i~ now input at the sensor device ~ at the terminal 3A.
On passlng through ~he sen~or device 3, the pol~rlzatlon plane of the linearly polarized second,light signal L2' ls rotated by a Faraday measurement angle dependent on the calibratlng magnetic field Ho~ which angle has the opposite sign, because of the non~eclprocal property of the ~araday effect, an~ the same quantity as the fi~t light signal Ll'. The second light sign~l L2', ro~ated in its polarization plane a~ou~ the measurement angle, is now delivered to the se~ond polarizer 6.
The second polarizer 6 allows only the component of the oncoming second light sign~l L~ that is projected on its polarization axi~ to pass throu~h, and thus act~ as a polarization analyzer of the second light signal ~'. The component of the second light signal L2' t~an~mitted by the second polarizer 6 1s r.ow designated ~2 and is transmitted ~o the evaluation means 20 via the first tran~mission path 4 and b~_Sg~l~r~ 2.
~, a first light signal ~1' 'ransmit~ed by the se~or.d polarizer i9 desig~ated L1 and is ~ransmitted to Ihe evcluatlon d~v'ce 20 through the second trarlsmission path 7 and the coupler 13 5 The second llght slg~al L2' first passe~ through the sec~~d tra~.s~'s~ion pa-~, 7 ar.G is then ;inearly polarized by the seccnd polarizer 6. ~he linearly polarized ~econd ligh;
slgn2l L2' i~3 inp.lt t~ tl~e sensor device 3 at the ter~r,iria ~B.
Upon passlng ~hro~gh ~he senso~ device 3, the polarization lo plane Oc the linearly polar zed second light ~ignal ~2~ is rotated by ~ Faraday -.,easure~,ent angle dependent or~ the ca'ibrating magne~ic lie_c rO. ~he an~e ~,a~ the oppcsl-e sign, ~ecause o~ .~.e ~c~-re~ p-ocal proper~y of the aradcy effect, and haq the same quantity as ~he fi~t lign~ signa Ll'. The ~econd ;i~.t slgIlal L2', wh;ch i9 rota'ed f-i its po_axiz~ion plane abo~t ~.e ~easureme~ angle, ls ther~
de i~ered to the f~st ~lar.zer 5. The 'i~st po:arizer 5 a~lows only the co~.ponen_ o~ the oncoming second ;ig~.t slc-nal L2 that i~ projected on its polariz~tion axis to pass ~hrou~,h, 2C and thu9 acts ac a polarization anal yzer of the ~eccn~ llFh~
signai L2' . The cc~ oner-t O r the second light slgna ~2' ~h_c;~ ansmi~ed by t'ne f'rst po'a~izer 5 is designated L2 and is ~ransmltted t:~roug;q tne firs~ transm~lon pa~h 4 an~
the co~le~ :2 ,o ~he e~a:~a~ o~ devlce ~0.
-lla-The light intensities I1' and I2' of the two light signal3 Ll' and L2', before being input into the series circuit, are generally set to a fixedly predetermined ratio to one another.
P~eferably, both light inten~ities are the same; that is, I1' = I2'. In the embodiments shown, the coupler 11 then splits the light L of the light source 10 into two equal parts wlth a coupling ratio of 50~:50%.
Upon traversing the two transmis5ion paths 4 and 7, both light signal~ L1' and ~1 an~ L2' and L2, respectivel~, ~ndergo the same change~ in intensity, which can be ~aused particularly by damping losses resulting from mechanical vi~ration. These changes in inten~ity are essentia:L~y expressed a~ damping factors in the light intenslties I1 and I2. The real damping ~actor, whlch is ~enerally time-dependent of an optical transmission path is define~ zs the ratio of the light intehSity of light arriving at one end of the transmis~ior path to the input light intensity as the light is input at the other end o~ the transmission path. The damping fac~ors OL
the transmlssion paths 4 ~nd 7 are now eliminated, in that the evaluation ~eans 2~ derive a quotient signal, in genexal in the for~ of a measurement signal M for the calibrating ma~neti~ ~ield Ho, which quotient signal takes the form M (a ~ I1 + b - I2 + c)/~d I1 ~ e ~ I2 + f) (1) from t~o llnear functions (a Il + b I2 + c) and ~d ~ I1 + e -I2 + f) of the two light intensities I1 and I2 wlth the real coefflcient~ a, b, c, d, e and f. At least elther the coefficient~ a and e, or the coefficients b and d, are othe~
than zero.
This meas~rement sign~l M is practically independen~ of changes in lntensity, caused in particuldr by vibration in the transmission paths 4 and 7. ~hu~ in all the embodi~ents, even d ~gc~ c~
.
~he simple, comparatively inexpensive telecommunications optical fibers (multimode fibers) can be used as the t~ansmis~ion paths 4 an~ 7, since the relatively high damplng and vibration sen~itivity of these fibers a~e compensated for in the measurement signal M. However, other optical fi~ers or free-beam arrays can also ~e used.
The coefficlents a, ~, c, d, e and f of the linear f~nctions in the numerator and denominator of equatlon (1) can ln particular be adapted to different input intensities of the two light signals upon ~e ng lnput into the serie~ circuit.
The coefficients d, e and ' of the linear function d I1 + e I2 + f in the denomlna~or of the quotient in equation (l) a-e prefe~ably set such that the linear function d ~ I1 + e ~ I2 +
f is practically constan~ and is t:hus independent o~ the ma~netic field Ho.
Particularly, when the input ir.tensities I1' and I2' of both liqht sign~ls L-1' and L2' are approximately the ~ame, lt is pos~ible in the advantageous e.~bodiment shown in Fi~. 3 also to use the quotient M = (Il - I2)/~I1 + I2~
of a di~ference I1 ~ I2 ~o~ I2 ~ and the sum I1 ~ I2 of the two light intenslties -1 and I2 after passing through the series circuit as the ~eas~rement signal M. In the embodiment shown, the e~aluatlon ~e~ns 20 for derivin~ the measurement signal M, have two photoelectric converters 21 and 22, a sub~ractor 23, an adder 24, an~ a dlvlder 25. The first converter 21 is optically connec~ed to the couple~ 13 and convert~ the first li~ht s_gna_ L1, a ter it has passed through the series circult, lr.to a first electrical intens~ty signal S1, whose signal irten~lty corresponds to the light intensity I1 of the first light signal L1. The second converter 22 is optically conr.ected to the coupler 12 and . ~ 89~0 ~N l'~ 0, 8vv. ~ a converts the second light 5ignal L2, after it h~s p~ssed through the serie~ circuit, into a second electrical intensity slgnal SZ as a measure of the light intenslty I2 of the second light signal L2. The two inten~ity signals S1 and 52 are e~c~
delivered to one input of the subtractor 23 and of the adder 24. T~e difference signal S1 - S2 ~or S2 - S1~ at the output of the subtractor 23 and the su~mation signal S1 I S2 at the output of the adde~ 24 are each delivered to one input o~ the divider ~S. The o~tput signal of the divider ~S1 - S2)/~S1 ~
s2~ is utilized as the measurement 3ignal M and is switched to one o~tput o~ the evaluatlcn mean9 20. This embodiment has the advantage that analog components, which a~ a rule are faste~, as digital component~.
In an embodiment not shown, the two electrical lntensity signals can also first be digitized, however, with the aid of an analog/digital converter, ~d then the ~itized signals can then be furtner processed by a microprocessor OL a digital signal processor.
~y adapting the coefficients a, b, c, d, e and f ln the general mea~urement ~ignal M = (a ~ I1 + ~ I2 + c)/(d ~ e ~ I2 + f), it is posslble in particular to compen~ate for different ~en~itivities o~ the two photoelectric converters 21 and 22.
The measurement array of Fig. 3 to be calibrated i~ preferably intended for mea~uring an electrlcal current I i~ at least one current conductor 2. The sensor device 3 then de~ects the magnetic f~ield generated induc_iv~3ly by this current I. The sensor device 3 pre~er~bly s~rr~nd~ the c~rre~t co~ductor ~, ~o that both light ~ignal~ L1' and L2' carry the current I in a practically closed light path. ~n thls case, the measurement angle is directly propo~tlona~ to the electrlcal current I. The sen~or device 3 lnay be embodied a~ a solid glass ring with ir.ner re~leot-ve ~aces that deflect the light :4 , d ~9~0 CN Ju~":0~ ~36i Til~5 51gnals Ll' sn~ L2', or may be embodied in some other known ~ay. The constant ~alibrating magnetic ~ield ~ can be set by adiusting a constant ~urrent I in the current conductor 2.
The temperature dependency of the measurement signal M is now essentially eliminated by means of the calibration method for temperature compensat~on descrlbed below. ~he calibration ls done by mean~ of the optimal setti.ng o~ the polarizer angles of the two polarizers 5 and k.
Figs. 4-6 show three po3sible calibration steps ~or settlng these optlmal polarizer angles of the polarizer~ 5 and 6. In Figs. 4- 6, a polarization axis (transmission axis, characteristic axis, intrinsic ax-s) of the ~irst polarizer 5 i9 desi~na~ed Pl, and a polarizatLon axi~ of the secorld polarizer 6 ls designated P2. ~he Dolarization axes Pl and P2 are located in a plane oriented perpendlcular to the light propagation direction of the l~.gh; passing ~hrough the polarizer~ 5 and 6. A reference axis, whlch can be predetermined arbitr~rily and is al50 loc~ted in this plane, i~ desi~nated R. The polarization axis Pl of the first polarizer 5 forms d first polarizer angle ~ with the predetermined ~eference ~xis R, while the polar~za~ion axis F~
of the second polarizer 6 is oriented ~t a ~econd polarizer angle ~ to the reference axi~ R.
In a first calibration step, the polarizer angle3 H and ~ of the two polarizers 5 and 6, re~pectively, ar~ set s~ch that maximUm ~mall-slgnal ~ensitlYity is achieved. To that end, the first polarizer angle H is set to a .irst calibration val~e ~ ~nd the second polarizer angle ~ is set to a first calibration value ~1, e~sentially in accor~ance with the equation sin(Z~l - 2~ 1 tla) ~1 c ~9~ o~ C~ 86c or sin(2~1 - 2~ 1 (lb).
With the thus-set polarizer angles ~ and ~ , the resultant measurement signal M i~ plotted as a first cali~ration signal M1 over a predetermlned tempe~ture r~nge, including at lea3t two temperature values, and is stored in memory. The temperature range is selected in accordance with the expected temperatures of use o~ ~he me~s~rement arr~y.
~ne or the other of the condltions (la~ or (lb) is met in particular i~ ~he polarization axes Pl and P2 fo~ an ~ngle of _ 45~ (i ~f4) with one another.
Fig. 4 shows an exemplary embodiment in which the polarizer angles ~ and ~ are set to calibration values ~1 and ~1~
respectively, that meet condition (la). The polariz~tlon axls P2 of the second polarizer 6 is inclined relatlve to the polarization axis P1 o~ the first polarizer 5 by the angle ~1 -~1 - +45~. Posltive angles here and below indicate the mathematically positive direction o~ revolution ~counterclockwi~e).
In a second calibration ~tep, the fir~t polarizer angle ~ i~
set to a cali~ration value ~2~ and the second polarizer angle is set to a calibration value ~, so that essentially the con~ition ~in~2~2 ~ 2~z~ 2 or sint2~z - 2~2~ 2b~
on the one h~nd, and at the same time the condition cost2~2 + 2~2) - -COS~(2~1 + 2~1~ (3) L, d ~9(~ C ~ ~66 ~, ~C"
on the other are met. With the thu~-set polarizer angles ~ -~2 and -- rl2~ the resultant measurement signal ~) is ascertained as a second cali~ration ~lgnal Mz over the predetermined temperature xange, and is llkewi3e stored in me~ory. ~o set the polarizer angles ~ and ~ to thelr second calibratlon values ~3z and ~2, it is possible for in~tance compared with the ~irst calibration values ~1 and ~1 to rotate the pol~rization axls P1 or P2 of one of the two polari~ers 5 and 6 farther by ~0~, or to rotate bo~h polarization axes ~1 and P2 farther, each by 45~.
Fig. 5 shows an e~peci~lly easily set embodiment of the second calihration s~ep. In compari~on to the setting in Fig. 4, the polarization axis P1 of the first polarize~ ~ ls unchan~ed;
that is, (31 ~ ~2, a~d only the second polarizer 6 i~ rotated by -9o~ relative to _he reference axis ~; that is, Tl2 = ~1~ + 90~-The angle formed by ~he two polarization axes P1 and P2 i9 then ~32 -~2 = -45~.
The calibration signals M1 a~d M2 obtained from the first calibration ~tep and the ~econd calibration ~tep are functions M1(T) a~d Mz(T), xespectively, of the temperature T over the predetermined t~mperature range and can be analytically de~cribed ln a good approximation a~ follow~:
M~ (~) =1+cos(2~l+~l)f2(T) M (~)= f'( ) = f'~ ) (5 1 + cos(2~ + 2r12 ) f2 (T) l-cos(2~l+~)f2 (T) ' v v u u N ~'V~ 7 ~ 6 6, , Solving the two equations (4) and ~5) for fl(T) and cos(2~1 +
2~) fz~T), and inserting a real correc~io~ factor K, leads to the equation for the calibration function:
M,~ (~) = M Jr A~ + K(M, -M2 ) ( 6 ) The correction factor K is preferably determined in a thlrd calibration step, by means of a simple numerical process and with the aid o~ a digltal signal processor or a mic~opxocessor, su~h that the temperature drift ~f the associated calibration function ~K~T) ~ecomes minimal. This means that the calibration function ~K = (2M1M2~/(M1-+ M~ + K -(M1 - M2)), which is dependent on the first calibration signal M~, the second calibration sign~l M2, and the correction f~ctor K, is essentially constant over the predetermined ~empera.u~e range.
If the predetermined temperature range (calibration range) includes only two temperature values T" and Tb~ then to that end, with the aid of the corresponding calibration ~ignal value~ M1(TA) and M2 (Ta~ ~ as well as Ml(Tb~ and M2(Tb~, the equation M~(Ta) -- MK~Tb) is simply solved for the correction factor K.
Conversely, if the predetermined temperature range includes more than two temperature measurement points, then y = f ~T~ =
2~2/(M2 - Ml) can be plotted in a graph relative to x = cos(2 + 2~)fz~T) = (M1 + M2)~(M2 - M1). Thl~ gra~h is fitted llnearly with the function Y~X) - MK(1 ~ KX) (8) 6~ d ~9'10 CN Wb~ 9. ~66. , i J~
with the fitting parametexs M~ and K.
In a four~h calibration step, the polarizer angles ~ and ~ of the two polari~ers 5 and 6 ~re now set ln accordance with Fi~.
6 in such a way that the resultant meas~rement ~ignal M has minimal ~emperatUre drift.
In a flrst embodi~ent of this fourth ca~i~ration step, the polarizer angles O and ~ of the two polarizers 5, 6 are adjusted such t~at es~enti~lly the equation~
~in~2~ - 2~) = l (9a~
or sin(2~ 2~ 9b) and co~(2~ + ~ cOs((2~1 i 2 l) (l~).
To that end, by way of example, t~e polarization axes Pl and P2 c~n be rotated, comp~red to the ~ettlng in Flg. 5, in the same direction by the same angle while maintaining the same angle of - 45~ (condition (9~ formed ~y the polarizatlon axes Pl and P2, until such time as condition (lO) i~ met. In a second embodlment of .he fourth calibration step, the polarizer angles ~ ~nd ~ of the two polarizers 5, 6 are adj~sted such that the resultant measuremen~ signal M, ~or at least one temperatur~ value TD from the predetermined temperature range, is substantially equal to the calibrat~on functlon M~, and accordingly:
M(TO) ~ M~(TO) (11).
In both the first em~odiment ln accordance with equa~ions ~9a), (9b) and ~lO), ~nd in th~ second embodiment in accordance wi~h equation (ll~ of the ~ourth calibratlon step, 0~ d ~9S0 ~N Wb~t: C, X~, ii, ~3u ., , . . ~ _ the two polarizer angles ~ and rl of the two polarizers 5 ~nd 6, re~pectively, are adjusted optlmally for ~inim~l temperature dependency o~ the measurement slgnal M in the predetermined ~emperature range.
Instead of the measurement signal M itself, in all the embodiments it is al90 possible to u3e the effective value of the measurement signai ~ for the temperature calibration, if alternatlng magnetic fielà9 are to ~e measured, One fundamental advantage of temperature compensatlon by setting the polarize~ angles ~ ~nd ~ i~ the high bandwidth upon measuring magnetic flelds H or elec~rical currents I.
The frequency spectrum of the magne~ic fields H or electrical currents I to be measured is not in fact limited in principle by the provisions made for temperature compensatlon.
i~ d v9~ ~~j t~'7: Ji ~iV'i -j, '
Claims (7)
1. A method for temperature calibration of an optical measurement array for measuring a magnetic field with an optical series circuit (1) comprising a first optical transmission path (4), a first polarizer (5) with a polarization axis (P1), which forms a first polarizer angle with a predetermined reference axis (R), a sensor device (3) that indicates the Faraday effect, a second polarizer (6) with a polarization axis (P2) that forms a second polarizer angle ~
with the reference axis (R), and a second optical transmission path (7), including the following method steps:
a) the sensor device (3) is disposed in a calibrating magnetic field (H0);
b) at least one light signal (L, L1, L2) passes through the optical series circuit (I);
c) from the light intensity (I, I1, I2) of the at least one light signal (L, L1, L2) after passing through the series circuit (1), a measurement signal (M) is ascertained for the calibrating magnetic field (H0);
d) in a first calibration step, the first polarizer angle .theta.
is set to a value .theta.1, and the second polarizer angle ~ is set to a value ~1, thus essentially meeting the condition, sin(2.theta.1 - 2~1) = 1, or sin(2.theta.1 - 2~1) = -1, and the resultant measurement signal is ascertained as a first calibration signal M1 over a predetermined temperature range including at least two temperature values;
e) in a second calibration step, the first polarizer angle .theta.
is set to a value .theta.2, and the second polarizer angle ~ is set to a value ~2, thus essentially meeting the conditions, sin(2.theta.2 - 2~2) = 1, or sin(2.theta.2 - 2~2) = -1, and cos(2.theta.2 + 2~2) = -cos (2.theta.1 + 2~2), and the resultant measurement signal is ascertained as a second calibration signal M2 over the predetermined temperature range;
f) in a third calibration step, a correction factor (K) is ascertained such that a calibration function Mx = (2-M-M2)/(M1 + M2 + K - (M2 - M2)), which is dependent on the first calibration signal (M1), the second calibration signal (M2) and the correction factor (K), is substantially constant over the predetermined temperature range;
g) in a fourth calibration step, the polarizer angles .theta. and ~
of the two polarizers (5, 6) are adjusted such that essentially the equations sin(2.theta. - 2~) - 1, or sin(2.theta. - 2~) = -1, and cos(2.theta. + 2~) = K ~ cos(2.theta.1 + 2~1), are met.
with the reference axis (R), and a second optical transmission path (7), including the following method steps:
a) the sensor device (3) is disposed in a calibrating magnetic field (H0);
b) at least one light signal (L, L1, L2) passes through the optical series circuit (I);
c) from the light intensity (I, I1, I2) of the at least one light signal (L, L1, L2) after passing through the series circuit (1), a measurement signal (M) is ascertained for the calibrating magnetic field (H0);
d) in a first calibration step, the first polarizer angle .theta.
is set to a value .theta.1, and the second polarizer angle ~ is set to a value ~1, thus essentially meeting the condition, sin(2.theta.1 - 2~1) = 1, or sin(2.theta.1 - 2~1) = -1, and the resultant measurement signal is ascertained as a first calibration signal M1 over a predetermined temperature range including at least two temperature values;
e) in a second calibration step, the first polarizer angle .theta.
is set to a value .theta.2, and the second polarizer angle ~ is set to a value ~2, thus essentially meeting the conditions, sin(2.theta.2 - 2~2) = 1, or sin(2.theta.2 - 2~2) = -1, and cos(2.theta.2 + 2~2) = -cos (2.theta.1 + 2~2), and the resultant measurement signal is ascertained as a second calibration signal M2 over the predetermined temperature range;
f) in a third calibration step, a correction factor (K) is ascertained such that a calibration function Mx = (2-M-M2)/(M1 + M2 + K - (M2 - M2)), which is dependent on the first calibration signal (M1), the second calibration signal (M2) and the correction factor (K), is substantially constant over the predetermined temperature range;
g) in a fourth calibration step, the polarizer angles .theta. and ~
of the two polarizers (5, 6) are adjusted such that essentially the equations sin(2.theta. - 2~) - 1, or sin(2.theta. - 2~) = -1, and cos(2.theta. + 2~) = K ~ cos(2.theta.1 + 2~1), are met.
2. A method for temperature calibration of an optical measurement array for measuring a magnetic field with an optical series circuit (1) comprising a first optical transmission path (4), a first polarizer (5) with a polarization axis (P1), which forms a first polarizer angle .theta.
with a predetermined reference axis (R), a sensor device (3) that indicates the Faraday effect, a second polarizer (6) with polarization axis (P2) that forms a second polarizer angle ~
with the reference axis (R), and a second optical transmission path (7), including the following method steps:
a) the sensor device (3) is disposed in a calibrating magnetic field (H0);
b) at least one light signal (L, L1, L2) passes through the optical series circuit (1);
c) from the light intensity (I, I1, I2) of the at least one light signal (L, L1, L2) after-passing through the series circuit (1), a measurement signal (M) is ascertained for the calibrating magnetic field (H0);
d) in a first calibration step, the first polarizer angle .theta.
is set to a value .theta.1, and the second polarizer angle ~ is set to a value ~1, thus essentially meeting the condition, sin(2.theta.1 - 2~1) = 1, or sin(2.theta.2 - 2~1) = -1, and the resultant measurement signal is ascertained as a first calibration signal M1 over a predetermined temperature range including at least two temperature values;
e) in a second calibration step, the first polarizer angle is set to a value H2, and the second polarizer angle ~ is set to a value ~2, thus essentially meeting the condition, sin(2.theta.2 - 2~2) = 1, or sin(2.theta.2 - 2~2) = -1, and cos(2.theta.2 + 2~2) = -cos((2.theta.1 + 2~1), and the resultant measurement signal is ascertained as a second calibration signal M2 over the predetermined temperature range;
f) in a third calibration step, a correction factor (K) is ascertained such that a calibration function Mx = (2 - M1 - M2) / (M1 + M2 + K ~ (M1 - M2)), which is dependent on the first calibration signal (M1), the second calibration signal (M2) and the correction factor (K), is substantially constant over the predetermined temperature range;
g) in a fourth calibration step, the polarizer angles .theta. and ~
of the two polarizers (5, 6) are adjusted such that the resultant measurement signal (M), for at least one temperature value from the predetermined temperature range, is substantially equal to the calibration function M K.
with a predetermined reference axis (R), a sensor device (3) that indicates the Faraday effect, a second polarizer (6) with polarization axis (P2) that forms a second polarizer angle ~
with the reference axis (R), and a second optical transmission path (7), including the following method steps:
a) the sensor device (3) is disposed in a calibrating magnetic field (H0);
b) at least one light signal (L, L1, L2) passes through the optical series circuit (1);
c) from the light intensity (I, I1, I2) of the at least one light signal (L, L1, L2) after-passing through the series circuit (1), a measurement signal (M) is ascertained for the calibrating magnetic field (H0);
d) in a first calibration step, the first polarizer angle .theta.
is set to a value .theta.1, and the second polarizer angle ~ is set to a value ~1, thus essentially meeting the condition, sin(2.theta.1 - 2~1) = 1, or sin(2.theta.2 - 2~1) = -1, and the resultant measurement signal is ascertained as a first calibration signal M1 over a predetermined temperature range including at least two temperature values;
e) in a second calibration step, the first polarizer angle is set to a value H2, and the second polarizer angle ~ is set to a value ~2, thus essentially meeting the condition, sin(2.theta.2 - 2~2) = 1, or sin(2.theta.2 - 2~2) = -1, and cos(2.theta.2 + 2~2) = -cos((2.theta.1 + 2~1), and the resultant measurement signal is ascertained as a second calibration signal M2 over the predetermined temperature range;
f) in a third calibration step, a correction factor (K) is ascertained such that a calibration function Mx = (2 - M1 - M2) / (M1 + M2 + K ~ (M1 - M2)), which is dependent on the first calibration signal (M1), the second calibration signal (M2) and the correction factor (K), is substantially constant over the predetermined temperature range;
g) in a fourth calibration step, the polarizer angles .theta. and ~
of the two polarizers (5, 6) are adjusted such that the resultant measurement signal (M), for at least one temperature value from the predetermined temperature range, is substantially equal to the calibration function M K.
3. The method of claim 1 or claim 2, in which a) the optical series circuit (1) is traversed by two light signals (L1, L2) in opposed directions of passage, and b) the measurement signal (M) is equivalent to the quotient between two linear functions of the light intensities (I1, I2 of the two light signals (L1, L2), in each case after they pass through the optical series circuit (1), or an effective valve of this quotient.
4. The method of claim 3, in which the measurement signal (M) is proportional to the quotient ((I1 - I2)/(I1 + I2)) between a difference and the sum of the light intensities (I1, I2) of the two light signals (L1, L2), in each case after their passage through the optical series circuit (1), or to an effective value of this quotient.
5. The method of claim 1 or claim 2, in which.
a) the optical series circuit (1) is traversed by a light signal (L);
b) a calibrating magnetic field (H0) with a substantially constant frequency spectrum above a predetermined frequency is used; and c) the measurement signal (M) is proportional to a quotient of an alternating component (I AC) of the light intensity (I) of the light signal (L) after passing through the series circuit (1) and a direct component (I DC) of this light intensity (I), and the alternating component (I AC) essentially includes the frequency spectrum of the calibrating magnetic field (H0), and the direct component (I DC) has no frequencies from the frequency spectrum of the calibrating magnetic field (H0).
a) the optical series circuit (1) is traversed by a light signal (L);
b) a calibrating magnetic field (H0) with a substantially constant frequency spectrum above a predetermined frequency is used; and c) the measurement signal (M) is proportional to a quotient of an alternating component (I AC) of the light intensity (I) of the light signal (L) after passing through the series circuit (1) and a direct component (I DC) of this light intensity (I), and the alternating component (I AC) essentially includes the frequency spectrum of the calibrating magnetic field (H0), and the direct component (I DC) has no frequencies from the frequency spectrum of the calibrating magnetic field (H0).
6. An optical measurement array for measuring a magnetic field (H) with an optical series circuit comprising a first optical transmission path (4), a first polarizer (5), whose polarization axis (P1) forms a first polarizer angle .theta. with a predetermined reference axis (R), a sensor device (3) indicating the Faraday effect, a second polarizer (6) whose polarization axis (P2) forms a second polarizer angle ~ with the reference axis (R), and a second optical transmission path (7), wherein the two polarizer angles .theta. and ~ are adjusted in accordance with a method as defined by one of claims 1-5.
7. The measurement array of claim 6, in which the sensor device (3) has a nonhomogeneous linear double refraction.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19623810.2 | 1996-06-14 | ||
| DE19623810A DE19623810C1 (en) | 1996-06-14 | 1996-06-14 | Temp calibration system for optical magnetic field measuring device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2258231A1 true CA2258231A1 (en) | 1997-12-24 |
Family
ID=7796982
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002258231A Abandoned CA2258231A1 (en) | 1996-06-14 | 1997-06-03 | Temperature calibration process for an optical magnetic field measurement device and measurement device calibrated by this process |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0904550B1 (en) |
| JP (1) | JP2000512386A (en) |
| CA (1) | CA2258231A1 (en) |
| DE (2) | DE19623810C1 (en) |
| WO (1) | WO1997048987A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10145764C1 (en) * | 2001-09-17 | 2002-11-21 | Siemens Ag | Magnetic field measuring method using Faraday effect uses linearly polarized light signals passed through magnetic field sensitive measuring path in opposite directions |
| PL1820034T3 (en) * | 2004-11-18 | 2010-03-31 | Powersense As | Compensation of simple fiberoptic faraday effect sensors |
| US8692539B2 (en) | 2006-11-30 | 2014-04-08 | Powersense A/S | Faraday effect current sensor |
| EP2919022A3 (en) * | 2007-11-30 | 2015-10-21 | PowerSense A/S | Sensor assembly and method for measuring strokes of lightning |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3364239D1 (en) * | 1982-03-08 | 1986-07-31 | Hitachi Ltd | Apparatus for optically measuring a current |
| US5008611A (en) * | 1989-03-14 | 1991-04-16 | Square D Company | Method of eliminating the effects of birefringence from the detection of electric current using Faraday rotation |
| DE4432146A1 (en) * | 1994-09-09 | 1996-03-14 | Siemens Ag | Method and device for measuring an electrical alternating current with temperature compensation |
-
1996
- 1996-06-14 DE DE19623810A patent/DE19623810C1/en not_active Expired - Fee Related
-
1997
- 1997-06-03 CA CA002258231A patent/CA2258231A1/en not_active Abandoned
- 1997-06-03 DE DE59704377T patent/DE59704377D1/en not_active Expired - Fee Related
- 1997-06-03 EP EP97930301A patent/EP0904550B1/en not_active Expired - Lifetime
- 1997-06-03 WO PCT/DE1997/001111 patent/WO1997048987A1/en active IP Right Grant
- 1997-06-03 JP JP10502056A patent/JP2000512386A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE19623810C1 (en) | 1997-07-10 |
| JP2000512386A (en) | 2000-09-19 |
| EP0904550B1 (en) | 2001-08-22 |
| EP0904550A1 (en) | 1999-03-31 |
| WO1997048987A1 (en) | 1997-12-24 |
| DE59704377D1 (en) | 2001-09-27 |
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