DE102007048817A1 - Sensor for measuring voltages in a substrate - Google Patents

Abstract

The invention relates to a sensor (1) for measuring stresses in a substrate (4), comprising at least one optical glass fiber (2) having at least one Bragg grating in the fiber core (3), wherein the optical glass fiber (2) of a primary coating (7) is surrounded, wherein the sensor (1) on the side facing away from the substrate (4) has a foil (5) and the optical glass fiber (2) without additional contact layer directly on the substrate (4) is glued. The described sensor (1) on the one hand has the advantage that, in contrast to the known sensor, no film is required in this case in order to avoid sticking of the skin. On the other hand, after an adhesive process, the optical glass fiber (2) touches the substrate (4). Thus, erroneous measurements are minimized.

Description

The The invention relates to a sensor for measuring voltages in a Substrate, with at least one optical fiber, at least a Bragg grating in the fiber core, wherein the optical fiber from a primary coating is surrounded.

Known is the stretching of a substrate by means of so-called strain gauges To measure (DMS). However, this technique is very vulnerable to electromagnetic Disorders. Besides, they are these strain gauges for an integration in composite materials to the so-called structural health monitoring unsuitable. To remedy this, were sensors designed on the basis of optical glass fibers.

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.

at Another known sensor is the glass fiber with the Bragg Grid glued sandwiched between two slides and then we the assembly adhered to a substrate.

One Disadvantage of this prior art is that when gluing the foils do not bear the optical glass fiber against the substrate, because the lower foil is between the two elements. This arrangement has the consequence that a transmission of a voltage the substrate into the optical glass fiber via the lower film got to. Leading usually 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.

Typically, the film is 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 a commercially available "optical Interrogator " which consists of a maximum of 128 sensors per channel is in the nanometer range. This "optical Interrogator "will used for data collection. He can use a 100 Hz sample frequency invest.

Of the Invention is based on the object, the sensor of the aforementioned Style to design such that in the voltage measurement in a Substrate avoided the erroneous measurements described above or minimized.

The solution This object is achieved by a sensor with the features of Claim 1. The sensor for measuring voltages in a substrate, with at least one optical fiber, the at least one Bragg Having grating in the fiber core, wherein the optical glass fiber of a primary coating is surrounded, is characterized in that the sensor on the The substrate facing away from the substrate has a film and the optical Fiberglass without additional Contact layer is glued directly to the substrate.

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 thin adhesive the optical fiber 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.

A advantageous embodiment of the sensor according to the invention is the adhesive strip symmetrically surrounds the optical glass fiber. Leading to a particularly stable construction of the sensor. In the presence more than one optical fiber, redundancy effects, because the optical glass fibers in the adhesive strip, in suitable intervals, Stabilize each other.

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

A further advantageous embodiment of the Invention provides that several glass fibers with inscribed Bragg gratings are arranged parallel to each other in a sensor. As a result, an advantageous redundancy is created, d. H. in case of failure A fiberglass can still be a meaningful measurement.

A further advantageous embodiment of the Invention provides that the glass fibers different Bragg Having gratings, d. H. have different refractive indices. This allows the measurements take place with different wavelengths.

Finally is the use of a sensor according to the invention for measuring Tensions in aircraft components, in particular in structural components especially advantageous. The sensors can also be used for long-term measurements in regular flight operations deploy. This takes the place of the substrate described above either part of the area or fuselage skin or equivalent support inside the aircraft.

The Invention will follow based on a preferred embodiment with the help of the attached Figures even closer described. Therefore, the figures are purely schematic. Same 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.

following are the same or similar Components 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 foil 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 Restricted invention in their execution not to the preferred embodiment given above. Rather, a number of variants are conceivable, which of the in the claims claimed solution also in other types Use.

1

sensor

2

optical glass fiber

3

fiber core

4

substratum

5

foil

6

Cured adhesive

7

primary coating

8th

Glue

9

protector

10

bonding adhesive

Claims (6)

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 ) is glued. Sensor according to claim 1, wherein a cured adhesive ( 6 ) the optical fiber ( 2 ) sheathed symmetrically. Sensor according to claim 1 or 2, 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 3, wherein a plurality of glass fibers ( 2 ) with burned Bragg grating parallel to each other in a sensor ( 1 ) are arranged. Sensor according to claim 4, wherein the glass fibers ( 2 ) have different Bragg gratings. Use of a sensor according to one of claims 1 to 5 for measuring stresses in aircraft components, in particular in Structural components.