Weldable strain sensor for curved surfaces

Abstract

A weldable strain sensor includes a strain sensor having two end portions in signal communication with signal lines for transmitting a measurement signal. A sensor carrier extends in a direction of the strain sensor and is firmly connected to the strain sensor. The sensor carrier includes two end portions having slots to thereby form tongues defining tongue ends which are directed in opposition to each other. Integrally surrounding the strain sensor and the end portions thereof is a protective cover of solid plastic which is firmly connected to the sensor carrier. The protective cover is configured in a region of the strain sensor narrow and flat and in a region of coupling points of the strain sensor with the signal lines at least twice as wide and at least twice as high as in a region of the strain sensor.

Claims

1. A weldable strain sensor, comprising: a strain sensor having two end portions coupled in signal communication with signal lines for transmitting a measurement signal, a sensor carrier extending in a direction of the strain sensor and firmly connected to the strain sensor, said sensor carrier including two end portions having slots to thereby form tongues defining tongue ends which are directed in opposition to each other; and a protective cover made of a solid plastic and integrally surrounding the strain sensor and the end portions thereof, said protective cover being firmly connected to the sensor carrier, said protective cover being configured in a region of the strain sensor narrow and flat and in a region of coupling points of the strain sensor with the signal lines at least twice as wide and at least twice as high as in a region of the strain sensor.

2. The weldable strain sensor of claim 1, wherein the tongues are trapezoidal.

3. The weldable strain sensor of claim 1, wherein the tongues are rectangular.

4. The weldable strain sensor of claim 1, wherein the tongues are semicircular.

5. The weldable strain sensor of claim 1, wherein each of the end portions of the sensor carrier has on both sides thereof 2 to 5 tongues, which oppose each other in pairs.

6. The weldable strain sensor of claim 1, wherein the tongues vary in length, with the tongue length decreasing in a direction of the strain sensor.

7. The weldable strain sensor of claim 1, wherein the tongues vary in width, with the tongue width increasing in a direction of the strain sensor.

8. The weldable strain sensor of claim 1, wherein the strain sensor is a glass or plastic fiber having a Bragg grating.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in more detail below with reference to schematic drawings:

(2) FIG. 1 shows a perspective view of a weldable strain sensor.

(3) FIG. 2a-2c show plan views of the strain sensor with welding points.

(4) FIG. 3 shows a perspective view of a strain sensor partially welded onto a tube.

(5) FIG. 4 shows the front view of the strain sensor of FIG. 3 partially welded onto the tube.

(6) FIG. 5a shows a perspective view of the strain sensor fully welded onto a tube.

(7) FIG. 5b shows an enlarged view of differently deflected tongues mounted on the tube.

(8) FIG. 6 shows tongues of different lengths.

(9) FIG. 7 shows tongues of different widths.

LIST OF REFERENCE SIGNS

(10) 1weldable strain sensor 2FBG strain sensor 3a, 3bsignal lines 4sensor carrier 5protective cover 6slots 7tongues 8 welding points

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(11) FIG. 1 shows a perspective view of a strain sensor 1 weldable onto curved surfaces. An FBG strain sensor 2 (concealed) is mechanically firmly connected and coupled in signal communication at its two end portions with signal lines 3a, 3b for conduction of the measurement signal. The FBG strain sensor 2 is bonded onto a sensor carrier 4 made of a sheet steel. The steel sheet in this exemplary embodiment has a thickness of 0.1 mm and a tensile strength of 884 N/mm.sup.2.

(12) The FBG strain sensor 2 and the signal lines 3a, 3b coupled thereto are completely covered by a protective cover 5 made of a solid plastic. In the present exemplary embodiment, epoxy resin is used because it is particularly strong and resistant to aging. The protective cover 5 is firmly connected to the sensor carrier 4. In the area of the FBG sensor 2, the protective cover 5 is narrow and flat, so as to be substantially as flexible as the thin sheet steel of the sensor carrier 4. The width of the protective cover 5 in the present embodiment is 2 mm in the area of the FBG strain sensor and the thickness is 0.5 mm. This ensures that when the sensor carrier 4 is welded onto a curved surface, the relatively hard protective cover 5 does not break. Likewise, the sensor carrier 4 is also narrower in this area than at the end portions thereof. In the present exemplary embodiment, the width of the end portions of the sensor carrier 4 is 23 mm and the portion there between is 11 mm wide.

(13) In the region of the coupling points, i.e. where the signal ones 3a, 3b are connected mechanically and in signal communication with the end portions of the FBG sensor 2, the protective cover 5 is at least twice as wide and at least three times as high as in the region of the strain sensor 2. In the present exemplary embodiment, the protective cover 5 in these areas is 10 mm wide, 18 mm long and 5 mm high.

(14) The free surfaces of the end portions of the sensor carrier 4 have slots 6 so as to form tongues 7 with ends that oppose one another.

(15) FIGS. 2a-2c show top views of the strain sensor and the sequence when setting welding spots 8. FIGS. 2a and 2b show that the welding spots 8 are set outwards starting from the middle of the sensor. Subsequently, the tongues 7 are welded, which also is implemented from the inside to the outside.

(16) FIG. 3 shows a perspective view of a strain sensor 2 partially welded onto a tube as shown in FIG. 2b. The tongues 7 are not yet welded.

(17) As is apparent from FIG. 4, the thick and thus very rigid end portions of the strain sensor 1 and the covers 5 as well as the signal lines 3a, 3b do not follow the curvature of the tube.

(18) FIG. 5a shows a completely welded-on strain sensor 1. FIG. 5b shows an enlarged view of the function of the tongues 7. It is apparent that the tongues 7 are differently deflected after their attachment to the tube surface.

(19) These tongues thus allow attachment of the entire strain sensor in a single work step. Consequently, no separate attachment technology is required for securing the thick and rigid end portions of the strain sensor 1. Since the plastic used for the cover of the class of epoxy resins is very resistant to various weather impacts, the need for an additional cover of the strain sensor is eliminated, so that the number of application steps is also reduced.

(20) FIG. 6 shows tongues 7 of different lengths, with the longest tongues located at the sensor end, since there the distance to the tube surface is the greatest.

(21) FIG. 7 shows tongues 7 of different width, with the narrowest tongues located at the sensor end, since there the distance to the tube surface is the greatest and the deformation forces can be kept small by a narrow tongue.

(22) By tongues of different length or different width in each end portion of the sensor carrier, the contact pressure required for spot welding can be kept approximately constant.