DE102007016158B4 - Measuring arrangement and measuring method with fiber Bragg grating measuring points - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35303—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using a reference fibre, e.g. interferometric devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
- G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
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Abstract
Messverfahren zur Erfassung und Auswertung mehrerer Messstellen (1, 2, 3) mit mindestens einem Lichtwellenleiter (10), in dem als Messstellen (1, 2, 3) mehrere Faser-Bragg-Gitter (1, 2, 3) mit unterschiedlichen Schwerpunkt-Faser-Bragg-Wellenlängen λM angeordnet sind, in die ein Lichtstrahl mit veränderlicher Wellenlänge λs periodisch einspeist wird, wobei die Intensitätsmaximas oder Peaks des reflektierten Lichtstrahles bei den verschiedenen durch die Faser-Bragg-Gitter (1, 2, 3) hervorgerufenen Intensitäts- oder Peak-Wellenlängen λM erfasst und ausgewertet werden, dadurch gekennzeichnet, dass die Lichtwellenlänge λs innerhalb der Periode T kontinuierlich von einer unteren Lichtwellenlänge λu bis zu einer oberen Lichtwellenlänge ansteigt und wieder abfällt, dass die Intensitätsmaximas des reflektierten Lichtstrahles in zeitlich beabstandete elektrische Messwerte (M1, M2, M3) umgewandelt werden, dass die elektrischen Messwerte (M1, M2, M3) entsprechend der zeitlichen Abfolge der von mehreren Messstellen (1, 2, 3) erzeugten Intensitätsmaximas zeitlich nacheinander einer Interpolationsvorrichtung (8) zugeführt werden und dass aus mindestens zwei zeitlich nacheinander erfassten Messwerten (M10, M1;...Measurement method for recording and evaluating several measuring points (1, 2, 3) with at least one optical fiber (10), in which several fiber Bragg gratings (1, 2, 3) with different focus points are used as measuring points (1, 2, 3) Fiber Bragg wavelengths λM are arranged into which a light beam with variable wavelength λs is periodically fed, the intensity maximas or peaks of the reflected light beam at the various intensity or intensity caused by the fiber Bragg grating (1, 2, 3) Peak wavelengths λM are detected and evaluated, characterized in that the light wavelength λs rises continuously from a lower light wavelength λu to an upper light wavelength and falls again within the period T, that the intensity maxima of the reflected light beam in time-spaced electrical measured values (M1, M2, M3) are converted so that the electrical measured values (M1, M2, M3) according to the time sequence of the meh rer measuring points (1, 2, 3) generated intensity maximas are supplied one after the other to an interpolation device (8) and that from at least two measured values (M10, M1; ...
Description
Die Erfindung betrifft eine Messanordnung mit Faser-Bragg-Gitter Messstellen gemäß dem Oberbegriff des Patentanspruchs 1 sowie ein Messverfahren mit derartigen Faser-Bragg-Gitter Messstellen gemäß dem Oberbegriff des Patentanspruchs 7.The invention relates to a measuring arrangement with fiber Bragg grating measuring points according to the preamble of
Faser-Bragg-Gitter-Sensoren sind robuste faseroptische Messfühler, die insbesondere zur hochauflösenden Erfassung von Dehnungen eingesetzt werden. Das Messprinzip derartiger Faser-Bragg-Gitter-Sensoren beruht darauf, dass in Durchstrahlrichtung eines Lichtwellenleiters eine periodische Änderung des Brechungsindexes als so genanntes Faser-Bragg-Gitter (FBG) eingebracht wird. Dieses Faser-Bragg-Gitter wirkt wie ein frequenzselektives Filter, deren Gitterkonstanten so gewählt sind, dass bei einem breitbandig eingestrahlten Licht ein sehr schmalbandiges Intensitätsmaximum als ein so genanntes Peak reflektiert wird. Entscheidend für die Lage (Schwerpunkt-Bragg-Wellenlänge) des Intensitätsmaximums ist dabei die räumliche Distanz innerhalb der periodischen Abfolge der Zonen mit unterschiedlichem Brechungsindex. Dies wird für den Einsatz von Messstellen mit solchen Faser-Bragg-Gitter-Sensoren vorzugsweise zur Erfassung von Dehnungen genutzt. Wird nun ein Lichtleiter im Bereich der periodischen Änderung des Brechungsindexes gedehnt oder gestaucht, so verändert sich die Lage des Intensitätsmaximums als Peak in seiner Wellenlänge λ. Diese Verschiebung der Wellenlänge λ lässt sich erfassen und im Sinne einer Bestimmung der Größe der verursachenden Dehnung auswerten. Es existieren mehrere Verfahren, um diese Wellenlängen bzw. Wellenlängenänderungen der reflektierten Intensitätsmaximal zu messen und daraus die Dehnungswerte zu ermitteln.Fiber Bragg grating sensors are robust fiber optic probes that are used in particular for the high-resolution detection of strains. The measuring principle of such fiber Bragg grating sensors is based on the fact that a periodic change in the refractive index is introduced in the direction of radiation of an optical waveguide as a so-called fiber Bragg grating (FBG). This fiber Bragg grating acts like a frequency-selective filter, the lattice constants of which are chosen such that, in the case of a broadband light, a very narrow-band intensity maximum is reflected as a so-called peak. Decisive for the position (focal Bragg wavelength) of the intensity maximum is the spatial distance within the periodic sequence of the zones with different refractive indices. This is used for the employment of measuring points with such fiber Bragg grating sensors preferably for the detection of strains. If an optical waveguide is stretched or compressed in the region of the periodic change in the refractive index, the position of the intensity maximum changes as a peak in its wavelength λ. This shift of the wavelength λ can be detected and evaluated in the sense of a determination of the size of the causative strain. There are several methods to maximally measure these wavelengths or wavelength changes of the reflected intensity and determine the strain values therefrom.
Mit dem so genannten Kantenfiltermessverfahren wird das reflektierte Licht über ein optisches Filter geführt, dessen Lichtdurchlässigkeit sich mit der Wellenlänge ändert. Verändert ein Reflexionspeak seine Wellenlänge, so ändert dies die Lichtintensität hinter dem Kantenfilter, was mittels Fotodioden gemessen werden kann. Dieses Verfahren ist einfach, hat aber die Nachteile, dass es nur ein einziges Faser-Bragg-Gitter auswerten, und kein Spektrum darstellen kann, sowie bei einer Streulichteinwirkung große Fehler zeigt.With the so-called edge filter measuring method, the reflected light is passed through an optical filter whose light transmittance changes with the wavelength. If a reflection peak changes its wavelength, this changes the light intensity behind the edge filter, which can be measured with photodiodes. This method is simple, but has the disadvantages that it can evaluate only a single fiber Bragg grating, and can not represent a spectrum, as well as showing large errors in a stray light exposure.
Bei dem so genannten CCD(Charge-coupled-device)-Messverfahren wird das reflektierte Intensitätsmaximum spektral aufgeweitet und dann auf eine CCD-Zeile projiziert. Die CCD-Zeile wird ausgelesen und die Wellenlänge der Reflexionspeaks durch eine Zuordnung zu den Pixeln der CCD ermittelt. Dieses Verfahren kann viele Faser-Bragg-Gitter auf einer Faser bzw. Wellenleiter messen und auch das Spektrum allerdings nur von einer Faser darstellen. Eine weitere Einschränkung besteht darin, dass dieses Verfahren zu tragbaren Kosten nur mit Silicium-CCDs ausfahrbar ist. Das bedeutet eine Beschränkung auf den Wellenlängenbereich um 800 nm, wodurch die verbreiteten und kostengünstigen Komponenten aus dem Telekommunikationsbereichen nicht nutzbar sind, da hier vorzugsweise im Wellenlängenbereich um 1550 nm gearbeitet wird.In the so-called CCD (charge coupled device) measuring method, the reflected maximum intensity is spectrally expanded and then projected onto a CCD line. The CCD line is read out and the wavelength of the reflection peaks is determined by an assignment to the pixels of the CCD. This method can measure many fiber Bragg gratings on a fiber or waveguide and also represent the spectrum of only one fiber. Another limitation is that this method is extendable at a reasonable cost only with silicon CCDs. This means a restriction to the wavelength range around 800 nm, whereby the widespread and inexpensive components from the telecommunications areas are not available, since it is preferably carried out in the wavelength range around 1550 nm.
Desweiteren ist zur Erfassung der jeweiligen Wellenlänge bzw. Wellenlängenänderung an Faser-Bragg-Gittern ein Messverfahren mit einem durchstimmbaren Laser bekannt. Bei diesem Messverfahren wird keine brandbandige Laserdiode zur Lichterzeugung eingesetzt, sondern ein Laser, der seine gesamte Strahlungsenergie in einer sehr kleinen Bandbreite (< 0,005 nm) abgibt. Die Wellenlänge des Lasers wird über einen Messbereich von beispielsweise 1500 nm bis 1600 nm und wieder zurück von 1600 nm bis 1500 nm in Form einer Dreiecksfunktion linear verändert. Bei den jeweiligen Peak-Wellenlängen der Faser-Bragg-Gitter gibt es starke Reflexionen. Das gesamte reflektierte Spektrum einer Faser bzw. Wellenleiters kann mit einer Fotodiode ermittelt werden, die während der Durchstimmung des Lasers die jeweils momentan rückreflektierte Strahlungsenergie misst. Infolge der hohen verfügbaren spektralen Energie des Lasers, die sich auf die sehr kleine Bandbreite konzentriert, lassen sich sehr große Mess-Störsignalabstände erreichen, die es erlauben, die Energie des Lasers auf viele Wellenleiter bzw. Fasern aufzuteilen, so dass die Anzahl der insgesamt anschließbaren Messstellen damit sehr groß werden kann. Dabei ist die Messgenauigkeit dieses Verfahrens auch sehr hoch. Dieses Messverfahren hat beim Einsatz vieler Messstellen mit Faser-Bragg-Gittern den Nachteil, dass ein relativ breiter Wellenlängenbereich nacheinander abgetastet werden muss, was insbesondere bei dynamischen Messungen bei einem zeitlich veränderlichen Dehnungsverlauf zu Wellenlängenänderungen während der Abtastzeiträume führen kann. Dadurch ergeben sich zeitabhängige Abweichungen, durch die bei einer vergleichenden Auswertung der Messergebnisse Fehler auftreten können.Furthermore, a measuring method with a tunable laser is known for detecting the respective wavelength or wavelength change on fiber Bragg gratings. In this measurement method, no brand-band laser diode is used to generate light, but a laser that emits its entire radiant energy in a very small bandwidth (<0.005 nm). The wavelength of the laser is linearly varied over a measuring range of, for example, 1500 nm to 1600 nm and back again from 1600 nm to 1500 nm in the form of a triangular function. There are strong reflections at the respective peak wavelengths of the fiber Bragg gratings. The entire reflected spectrum of a fiber or waveguide can be determined with a photodiode, which measures the momentarily reflected back radiation energy during the tuning of the laser. Due to the laser's high spectral energy, which is concentrated on the very small bandwidth, it is possible to achieve very large S / N ratios, which allow the energy of the laser to be divided among many waveguides or fibers, so that the total number of connectable Measuring points can become very large. The measurement accuracy of this method is also very high. This measurement method has the disadvantage of using many measuring points with fiber Bragg gratings that a relatively wide wavelength range must be scanned sequentially, which can lead to wavelength changes during the sampling periods, especially in dynamic measurements with a time-varying strain curve. This results in time-dependent deviations, which can lead to errors in a comparative evaluation of the measurement results.
Aus der
Aus dem Artikel von S. H. Yun, D. J. Richardson und B. Y. Kim „Interrogation of fiber grating sensor arrays wuth a wavelength-swept fiber laser”, Optics Letters, Vol. 23, S 843–845, 1998, ist bekannt, eine Wiederholfrequenz von Wellenlängen eines Lichtstrahls linear ansteigend in Form einer Messrampe zu erzeugen. Dabei ist insbesondere eine Wiederholfrequenz der Wellenlängenvariationen von 250 Hz genannt, die nur einen vorteilhaften Teilaspekt bei Faser-Bragg-Gitter-Sensoren beschreibt.From the article by SH Yun, DJ Richardson and BY Kim "Interrogation of fiber grating sensor arrays wuth a wavelength-swept fiber laser", Optics Letters, Vol. 23, pp. 843-845, 1998, it is known to have a repetition frequency of one wavelength Light beam linearly increasing in the form of a measuring ramp to produce. In particular, a repetition frequency of the wavelength variations of 250 Hz is mentioned, which describes only one advantageous partial aspect in fiber Bragg grating sensors.
Der Erfindung liegt deshalb die Aufgabe zugrunde, eine verbesserte Messanordnung und Messverfahren zur Ermittlung von Faser-Bragg-Gitter-Reflexionswellenlängen zu schaffen, die einen einfachen Aufbau besitzt, für dynamische Messungen geeignet ist und eine simultane Erfassung der Messergebnisse mit einer Vielzahl von Faser-Bragg-Gittern ermöglicht.The invention is therefore based on the object to provide an improved measuring arrangement and measurement method for determining fiber Bragg grating reflection wavelengths, which has a simple structure, is suitable for dynamic measurements and simultaneous detection of the measurement results with a variety of fiber Bragg - allows lattices.
Diese Aufgabe wird durch die in Patentanspruch 1 und Patentanspruch 7 angegebene Erfindung gellst. Weiterbildungen und vorteilhafte Ausführungsbeispiele sind in den Unteransprüchen angegeben.This object is achieved by the invention specified in
Die Erfindung hat den Vorteil, dass durch eine einfache Interpolationsvorrichtung eine optische Messanordnung mit einem durchstimmbaren Laser auch zur dynamischen Messung bei einem zeitlich veränderlichen Dehnungsverlauf mit einer Vielzahl von Faser-Bragg-Gittern einsetzbar ist. Dabei werden durch die Interpolationsvorrichtung aus den zeitlich nacheinander erfassten Messwerten für alle Faser-Bragg-Gitter Messstellen simultane Messwerte errechnet, die dann insbesondere bei dynamischen Messungen eine hohe Messgenauigkeit gewährleisten. Dieses Messverfahren hat gleichzeitig den Vorteil, dass die dann simultan vorliegenden Messwerte vergleichend oder auf andere Art gleichzeitig ausgewertet werden können.The invention has the advantage that, by means of a simple interpolation device, an optical measuring arrangement with a tunable laser can also be used for dynamic measurement with a time-varying strain profile with a large number of fiber Bragg gratings. The interpolation device calculates simultaneous measured values for all fiber Bragg grating measuring points from the measured values recorded in chronological succession, which then ensure a high measuring accuracy, particularly in the case of dynamic measurements. At the same time, this measurement method has the advantage that the measured values which are then present at the same time can be evaluated simultaneously or in a different manner at the same time.
Zusätzlich hat die Erfindung den Vorteil, dass mit einem einzigen durchstimmbaren Laser eine hohe Anzahl von Messstellen ausgewertet werden kann, und gegenüber Breitband-Lichtquellen eine verhältnismäßig hohe Lichtintensität zur Verfügung steht, die auch bei einer Vielzahl von Messstellen verhältnismäßig hohe Reflexionsenergien ermöglicht, die wegen des großen Störsignalabstandes einfach und auch bei zeitlich veränderlichen Dehnungsverlauf noch hochgenau detektierbar sind.In addition, the invention has the advantage that with a single tunable laser, a high number of measuring points can be evaluated, and compared to broadband light sources, a relatively high light intensity is available, which allows relatively high reflection energies even at a plurality of measuring points, due to the large Störsignalabstandes are easy to detect and even with time-varying strain curve highly accurate.
Eine besondere Ausführung der Erfindung mit einer linearen Interpolationsvorrichtung hat den Vorteil, dass dadurch insbesondere bei einem kontinuierlichen zeitlich veränderlichen Dehnungsverlauf genaue Dehnungsmessungen in und an Festkörpern zur vergleichenden Auswertung durchführbar sind. Dies ist insbesondere bei der Auswertung einer Vielzahl von Messstellen zur Dehnungsmessung vorteilhaft, da dort relativ große Messzeitunterschiede auftreten und diese rechnerisch wegen der linearen Dehnungsvorgänge sehr genau auf einen simultanen Bezugszeitpunkt interpoliert werden können.A particular embodiment of the invention with a linear interpolation device has the advantage that exact strain measurements in and on solids for comparative evaluation can be carried out thereby, in particular in the case of a continuous, temporally variable strain profile. This is particularly advantageous in the evaluation of a plurality of measuring points for strain measurement, since relatively large measuring time differences occur there and they can be mathematically very accurately interpolated due to the linear strain processes to a simultaneous reference time.
Die Erfindung wird anhand eines Ausführungsbeispiels, das in der Zeichnung dargestellt ist, näher erläutert. Es zeigen:The invention will be explained in more detail with reference to an embodiment which is illustrated in the drawing. Show it:
In
Dazu wird zunächst in einem durchstimmbaren Laser
In
Innerhalb dieser Durchlaufzeit werden von jedem Faser-Bragg-Gitter
In einem nachfolgenden Analog-Digital-Wandler
Bei einem zeitlich veränderlichen Dehnungsverlauf würde sich durch diese Messzeitdifferenz ein Messfehler ergeben, der nicht unbeträchtlich sein kann. Deshalb schlägt die Erfindung ein Messverfahren mit einer Messanordnung vor, das unabhängig von den Abfragezeitpunkten tM1, tM2, tM3, ist und für alle Messstellen
Die Durchlaufzeitpunkte tM1₀, tM2₁, tM3; tM1₀, tM1₀, tM3₀ der einzelnen vom Laser
Die durch die Interpolation durchgeführte Korrekturrechnung stimmt nur dann genau, wenn die Messgröße sich verhältnismäßig langsam mit konstanter Steigung ändert, wie dies oft bei Dehnungen an oder in Dehnungs- oder Testkörpern stattfindet. In diesen Fällen ist eine lineare Interpolation zwischen zwei Messwerten ausreichend. Allerdings ist es auch möglich, sehr genaue simultane Messwerte zu errechnen, wenn die Messgröße sich nicht gleichmäßig ändert, sondern nach einem Sinus verläuft. In diesen Fällen ist es jedoch erforderlich, mit einer höheren Ordnung der Interpolation zu arbeiten. Eine Interpolation dritter Ordnung ist z. B. nach Lagrange oder Newton möglich, bei der vier Messwerte zur Berechnung herangezogen werden und auch sehr gute simultane Messwerte liefern.The correction calculation carried out by the interpolation is accurate only if the measured variable changes relatively slowly with a constant slope, as is often the case with strains on or in strainers or test bodies. In these cases, a linear interpolation between two measured values is sufficient. However, it is also possible to calculate very precise simultaneous measured values if the measured variable does not change uniformly, but runs according to a sine wave. In these cases, however, it is necessary to work with a higher order of interpolation. A third-order interpolation is z. For example, according to Lagrange or Newton, in which four measured values are used for the calculation and also provide very good simultaneous measured values.
Die Errechnung der linearen simultanen Messwerte RM in der Interpolationsvorrichtung
- CM2
- = ein Koeffizient als Funktion der gemessenen Peak-Zellenlänge λM2;
- TM
- = die Zeit, in der der Messbereich (z. B. 1500–1600 nm) durchlaufen wird (hier z. B. 0,5 s);
- T
- = die Messperiode (z. B. hier = 1 s);
- λM2
- = die Wellenlänge des gemessenen Reflexions-Peaks;
- λmin
- = 1500 nm, und
- λmax
- = 1600 nm.
- C M2
- = a coefficient as a function of the measured peak cell length λ M2 ;
- T M
- = the time in which the measuring range (eg 1500-1600 nm) is traversed (here, for example, 0.5 s);
- T
- = the measuring period (eg here = 1 s);
- λ M2
- = the wavelength of the measured reflection peak;
- λ min
- = 1500 nm, and
- λ max
- = 1600 nm.
Aus den errechneten Koeffizienten CM2 als Funktion der gemessenen Reflexionswellenlänge λM2, für die Messstelle
- RM2
- = der errechnete simultane Messwert;
- M20
- = der ältere gemessene Messwert, und
- M21
- = der neuste gemessene Messwert.
- R M2
- = the calculated simultaneous reading;
- M2 0
- = the older measured value, and
- M2 1
- = the newest measured value.
Dazu werden zunächst auf der ansteigenden Messrampe
Die Interpolationsvorrichtung
Einen derartigen Mess- und Interpolationsvorgang und man vorzugsweise in periodischen Abständen wiederholen, so dass daraus dann in der Auswertevorrichtung
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S. H. Yun, D. J. Richardson und B. Y. Kim: Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser. In: Optics Letters, vol.23 (11), 1998, 843-845. * |
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