DE102007048817B4 - Sensor for measuring voltages in a substrate - Google Patents

Abstract

Sensor (1) for measuring voltages in a substrate (4), comprising at least one optical glass fiber (2) having at least one Bragg grating in the fiber core (3), said optical glass fiber (2) surrounded by a primary coating (7) is, characterized in that the sensor (1) on the side facing away from the substrate (4) has a film (5) and the optical glass fiber (2) without additional contact layers directly on the substrate (4) is glued, wherein a cured adhesive (6) the optical glass fiber (2) sheathed symmetrically.

Description

The invention relates to a sensor for measuring voltages in a substrate, comprising at least one optical glass fiber, which has at least one Bragg grating in the fiber core, wherein the optical glass fiber is surrounded by a primary coating.

It is known to measure the elongation of a substrate by means of so-called strain gauges (DMS). However, this technique is very susceptible to electromagnetic interference. In addition, these strain gages are unsuitable for integration in composite materials for structural health monitoring. To remedy this situation, sensors based on optical fibers were designed.

Such a sensor is known from the prior art. This one is in 2 illustrated schematically by way of example. Thereafter, the device consists of an optical fiber 2 with burned Bragg grids in the fiber core 3 , a slide 5 and a glue 8th , The foil 5 usually consists of various organic materials and covers the optical fiber 2 , The sensor is on a substrate 4 attached.

The optical fiber 2 is with the glue 8th on the substrate 4 glued to stress in substrate 4 to eat. The procedure is as follows. First, the glue 8th on the substrate 4 applied. Next is the optical fiber 2 with the help of the foil 5 on the substrate 4 pressed. After a few minutes the glue 8th is cured, the film is 5 away.

As already stated, you can see from 2 in that the device after removing the film 5 from an optical fiber 2 with Bragg grids in the fiber core 3 consists of a substrate 4 and a glue 8th ,

It is usually a teflon film as a film 5 used in the manufacture of the sensor, to avoid sticking to the human skin and thus when using a thin adhesive 8th , the optical fiber 2 not completely wetted.

In many cases, in this procedure, in the fiber core 3 inscribed Bragg grille is not exactly in the middle of the glue 8th to be adjusted.

In another known sensor, the glass fiber with the Bragg grating is sandwiched between two films and then we glued the assembly to a substrate.

A drawback of this prior art is that when the foils are bonded, the optical glass fiber does not abut the substrate, since the lower foil is located between the two elements. This arrangement has the consequence that a transfer of a voltage from the substrate into the optical glass fiber must take place via the lower film. This usually leads to erroneous measurements.

• 1, Markieren der Position des Sensors.
• 2, Reinigen von zurückbleibenden Verschmutzungen mit einem weichen Putzmittel.
• 3, Mechanische Abrasion des Verbinde-Bereichs.
• 4, Reinigen von Verschmutzung mit zusammengepresster Luft oder mit Pinsel.
• 5, Gründliches Reinigen des Verbinde-Bereichs mit Hilfe von Azeton oder gleichwertigen Reinigungsagenten.
• 6, Volles Lufttrocknen des Verbinde-Bereichs.
• 7, Anfängliche adhäsive Vorbereitung durch das Vermischen von Zutaten (Resin-Catalyst).
• 8, Anwenden einer dünnen adhäsiven Schicht über dem Verbinde-Bereich und dem Patch-Sensor.
• 9, Anordnen des Patch-Sensors über dem Verbinde-Bereich.
• 10, Andrücken des Sensors.

In general, the film is designed as a "patch". The "patch sensor connection" process involves the following steps:

• 1, marking the position of the sensor.
• 2, Clean remaining dirt with a soft detergent.
• 3, Mechanical abrasion of the bonding area.
• 4, cleaning pollution with compressed air or brush.
• 5, Thorough cleaning of the joint area using acetone or equivalent cleaning agent.
• 6, Full air drying of the bonding area.
• 7, Initial adhesive preparation by mixing ingredients (Resin Catalyst).
• Figure 8, Applying a thin adhesive layer over the bonding area and the patch sensor.
• 9, placing the patch sensor over the connect area.
• 10, pressing the sensor.

The wavelength of a commercially available "optical interrogator", which consists of a maximum of 128 sensors per channel, is in the nanometer range. This "optical interrogator" is used for data collection. He can create a 100 Hz sample frequency.

From the GB 2 145 515 A For example, a sensor for measuring voltages or detecting cracks in a substrate is known. The sensor consists of two optical fibers, with a first fiber located near the substrate to be measured and used to measure the voltage or the detection of cracks in the substrate, while a second fiber is located farther from the substrate than the first fiber, thereby is less susceptible to the strains of the substrate and serves to control the proper functioning of the overall device. Both the first and second fibers are secured to a body which is attached by side wings to the substrate to be measured and through which the stresses in the substrate are transferred into the fibers. The measuring principle of the substrate voltage is based on the measurement of the change in the light intensity through the first fiber. As the substrate expands, the body and thus the first optical fiber is also stretched, changing its diameter and that in the detector incoming light intensity of the detector also changed. From the change in the light intensity can be further deduced on impinging voltages in the substrate. In extreme cases, the first fiber breaks through, which greatly reduces the signal.

Also the EP 1 014 123 A2 and the DE 698 30 254 T2 describe optical sensors for measuring separations or strains in substrates.

The invention has for its object to design the sensor of the type mentioned above such that during the voltage measurement in a substrate, the erroneous measurements described above are avoided or minimized.

The solution of this object is achieved by a sensor having the features of claim 1. The sensor for measuring voltages in a substrate, comprising at least one optical fiber having at least one Bragg grating in the fiber core, the optical fiber being surrounded by a primary coating, is characterized in that the sensor on the side facing away from the substrate has a film and the optical glass fiber is glued directly to the substrate without additional contact layer.

With the solution according to the invention in contrast to the known sensor no film needed to avoid sticking of the skin and thus a low-viscosity adhesive, the optical glass fiber is not completely wetted. In the solution according to the invention, after the bonding process, the optical glass fiber contacts the substrate. Thus, erroneous measurements are minimized because a direct transfer of the voltage from the substrate into the optical glass fiber is made possible here and does not have to take place via an additional film, as in the case of the known sensor. This protective film protects the sensor assembly from contamination and is removed before placing the sensor on the substrate. The Teflon film used for the patch production remains after hardening of the adhesive strip on its side facing the substrate and thus provides until the final application protection for the fiber from external influences, such as dirt, grease, mechanical stress, etc.

An advantageous embodiment of the sensor according to the invention is that the adhesive strip envelops the optical fiber symmetrically. This leads to a particularly stable construction of the sensor. In the presence of more than one optical fiber, redundancy effects arise because the optical fibers in the tape stabilize each other at appropriate intervals.

Preferably, the sensor according to the invention is operated in the range of 1520 to 1570 nm, in which case the structure of the sensor is not the limiting factor.

A further advantageous embodiment of the invention provides that a plurality of glass fibers with inscribed Bragg gratings are arranged parallel to one another in a sensor. As a result, an advantageous redundancy is created, d. H. in case of failure of a glass fiber can still be made a meaningful measurement.

A further advantageous embodiment of the invention provides that the glass fibers have different Bragg gratings, d. H. have different refractive indices. As a result, the measurements can be made with different wavelengths.

Finally, the use of a sensor according to the invention for measuring stresses in aircraft components, in particular in structural components, is particularly advantageous. The sensors can also be used for long-term measurements in regular flight operations. In this case, takes the place of the substrate described above, either a part of the surface or hull planking or corresponding carrier in the interior of the aircraft.

The invention will be described in more detail below with reference to a preferred embodiment with the aid of the attached figures. Therefore, the figures are purely schematic. Identical or similar components are designated by the same reference numerals.

1a and 1b shows a schematic cross-sectional view of an advantageous embodiment of a sensor according to the invention;

2 shows a schematic cross-sectional view of a sensor according to the prior art.

Hereinafter, the same or similar components are designated by the same reference numerals.

1a shows a schematic cross-sectional view of an advantageous embodiment of a sensor according to the invention 1 in the assembled state. 1b shows the same sensor 1 as in 1a but before application to a substrate 4 ,

The sensor 1 which is used to measure voltages on a substrate 4 is used, has an optical fiber 2 on which is a registered Bragg grid in the fiber core 3 having. The optical fiber 2 is from a primary coating 7 surround.

The optical fiber 2 consist of a fiber core 3 , a coat and a coating, the so-called primary coating 7 , The light-guiding fiber core 3 serves to transmit a signal. The jacket is also light-guiding, but has a lower refractive index than the core. The jacket causes a total reflection and thus a guidance of the radiation in the fiber core 3 the fiberglass 2 , The primary coating 7 the fiberglass 2 consists of a soft plastic and is in the present embodiment between 150 and 500 microns thick.

The writing of the Bragg grating into the fiber core 3 the fiberglass 2 takes place at a defined location by means of UV laser radiation. That in the fiber core 3 Integrated Bragg gratings have the property of reflecting light of a particular wavelength, which is determined by the grating parameters. The Bragg Refelexionswellenlänge is sensitive to temperature and strain at the grid location and therefore serves to measure these sizes.

To mechanical stress measurement in the substrate 4 To avoid or minimize the erroneous measurements occurring in the known sensors according to the prior art, the sensor according to the invention has 1 at the substrate 4 opposite side of a slide 5 on, which is formed in the present embodiment as a Kapton foil. The optical fiber 2 is with a cured adhesive 6 formed adhesive strip on the film 5 stabilized, thus without additional contact layer on the substrate 4 to be able to lie. The displacement-free connection between the sensor 1 and the substrate 4 takes place in the present embodiment by a thin layer of bonding adhesive 10 , which is applied to the substrate at the measuring point.

As in 1b shown is the cured adhesive 6 of the sensor 1 via an easily detachable adhesive bond with a protective film 9 bonded. The protective film 9 is designed in the present embodiment as a Teflon film. Before applying the sensor 1 on the substrate 4 can this protective film 9 from the substrate 4 facing side of the sensor 1 subtracted from. This protective film 9 Protects the fiber from external influences, such as dirt, grease and other interfering contaminants, and saves additional cleaning of the patch surface before mounting.

The invention is not limited in its execution to the above-mentioned preferred embodiment. Rather, a number of variants is conceivable, which makes use of the claimed in the claims solution even in other types.

LIST OF REFERENCE NUMBERS

1

sensor

2

optical fiber

3

fiber core

4

substratum

5

foil

6

Cured adhesive

7

primary coating

8th

Glue

9

protector

10

bonding adhesive

Claims (5)

Sensor ( 1 ) for measuring voltages in a substrate ( 4 ), with at least one optical fiber ( 2 ), which has at least one Bragg grating in the fiber core ( 3 ), wherein the optical glass fiber ( 2 ) of a primary coating ( 7 ), characterized in that the sensor ( 1 ) at the substrate ( 4 ) side facing away from a film ( 5 ) and the optical fiber ( 2 ) without additional contact layers directly on the substrate ( 4 ), with a cured adhesive ( 6 ) the optical fiber ( 2 ) sheathed symmetrically. Sensor according to claim 1, wherein the sensor ( 1 ) is operated with burned-in Bragg grating in the range of 1520 to 1570 nm. Sensor according to one of claims 1 to 2, wherein a plurality of glass fibers ( 2 ) with burned Bragg grating parallel to each other in the sensor ( 1 ) are arranged. Sensor according to claim 3, wherein the glass fibers ( 2 ) have different Bragg gratings. Use of a sensor according to one of claims 1 to 4 for measuring stresses in aircraft components, in particular in structural components.

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