Strain gauge and metal strip having a strain gauge of this kind

Abstract

A strain gauge and a metal strip having such a strain gauge, which has a first measuring grid, a second measuring grid, and a substrate on which these two measuring grids are positioned in a common plane. In order to enable achievement of an inexpensive strain gauge whose measurement results can be robustly compensated for in relation to a temperature disturbance variable, it is proposed that the multi-layer substrate have a metallic layer and an electrically insulating layer onto which electrically insulating layer these two measuring grids consisting of a piezoresistive material are printed.

Claims

1. A strain gauge comprising: a first measuring grid; a second measuring grid; and a multi-layer substrate on which the first and second measuring grids are positioned in a common plane, wherein the multi-layer substrate has a metallic layer and an electrically insulating layer, the first and second measuring grids each consisting of a piezoresistive material are printed directly onto a first surface of the electrically insulating layer, and a second surface of the electrically insulating layer faces the metallic layer, and wherein the strain gauge counteracts temperature disturbance variables.

2. The strain gauge according to claim 1, wherein the second measuring grid oriented at a right angle to the first measuring grid is embodied as a passive measuring grid for temperature compensation of strain measurement values of the first measuring grid for which purpose the first and second measuring grids consist of the same piezoresistive material.

3. The strain gauge according to claim 2, wherein the first and second measuring grids have the same nominal resistance.

4. The strain gauge according to claim 2, wherein the first and second measuring grids each have at least one meandering grid section, with one grid section of the first measuring grid being positioned between two grid sections of the second measuring grid.

5. The strain gauge according to claim 4, wherein each of the first and second measuring grids has a plurality of meandering grid sections, which grid sections are positioned one after the other in alternating fashion.

6. The strain gauge according to claim 4, wherein a grid section of the first measuring grid has two meandering rows extending next to each other.

7. The strain gauge according to claim 4, wherein a ratio of at least one grid length of a first grid section to at least one grid width of a second grid section is 1:0.75 to 1:1.25.

8. The strain gauge according to claim 4, wherein the grid sections of the respective measuring grids are embodied as identically shaped, in particular as identical.

9. The strain gauge according to claim 1, wherein the first and second measuring grids are identically oriented and, as active measuring grids, have respective piezoresistive materials with temperature coefficients that are different from each other and strain factors that are different from each other.

10. The strain gauge according to claim 9, wherein the first and second measuring grids each have a meandering grid section.

11. The strain gauge according to claim 10, wherein the grid sections are positioned one inside the other and are identically shaped.

12. The strain gauge according to claim 9, wherein the two measuring grids extend in a double meander.

13. The strain gauge according to claim 1, wherein the metallic layer of the substrate is an aluminum strip or steel strip or is a plate made of aluminum or steel.

14. The strain gauge according to claim 1, wherein the electrically insulating layer of the substrate is a primer or an insulating lacquer layer or an organic or inorganic pre-coating.

15. A metal strip having a coating and having a strain gauge according to claim 1, wherein the metal strip constitutes the metallic layer of the substrate of the strain gauge and the coating on the metal strip constitutes the electrically insulating layer of the substrate of the strain gauge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject of the invention is shown in greater detail in the figures by way of example based on an embodiment variant. In the drawings:

(2) In the figures, the subject of the invention is depicted in greater detail by way of example based on several embodiment variants. In the drawings:

(3) FIG. 1 shows a top view of a strain gauge having several measuring grids according to a first exemplary embodiment,

(4) FIG. 1a shows a partially cut-away side view according to I-I in FIG. 1, and

(5) FIG. 2 shows a top view of a strain gauge having several measuring grids according to a second exemplary embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The strain gauge 1 according to a first exemplary embodiment, which is shown by way of example in FIGS. 1 and 1a, has a first measuring grid 2 and a second measuring grid 3. The first measuring grid 2 takes shape between the two connections 20.1 and 20.2—the second measuring grid 3 takes shape between the two electrical connections 30.1 and 30.2, both measuring grids 2, 3 being short-circuited at the ends to the connections 20.2 and 30.2. The two measuring grids 2, 3 are provided on a substrate 4 and positioned in a common plane 9. As is clear in FIGS. 1 and 1a, these measuring grids 2, 3 are provided laterally next to each other on the substrate 4.

(7) According to the invention, the multi-layer substrate 4 has a metallic layer 5 and an electrically insulating layer 6, which is depicted in FIG. 1a. To achieve this, the electrically insulating layer 6 is positioned on the metallic layer 5.

(8) The electrically insulating layer 6 can, for example, be a primer or an undercoat, coating, etc. of a sheet, strip, plate, slit strip, support, etc. on the metallic layer 5, which sheet, strip, slit strip, plate, support, etc. constitutes the metallic layer 5, for example. The metallic layer 5, the electrically insulating layer 6, and the two measuring grids 2, 3 and 102, 103, are positioned one above the other in layers. Preferably, the electrically insulating layer 6 covers the entire surface of the metallic layer 5.

(9) A comparatively good thermal coupling of the two measuring grids 2, 3 and 102, 103, via the metallic layer 5 of the substrate 4 can be achieved by means of this multi-layer substrate 4, as a result of which it can consequently be assumed that an identical temperature disturbance variable is present on the two measuring grids 2, 3 and 102, 103. This also makes the measuring grids 2, 3 and 102, 103 short-circuit-proof relative to the metallic layer 5 due to presence of the electrically insulating layer 6. The substrate 4 can have other layers, which is not shown.

(10) In addition, both of the measuring grids 2, 3 are printed onto the substrate 4, to be precise, onto the electrically insulating layer 6, which allows them to be provided close to one another without short-circuiting. For this purpose, the electrically insulating layer 6 electrically insulates the two measuring grids 2, 3 relative to the metallic layer 5 of the substrate 4. A piezoresistive material is used for the printing, for example silver-based or graphite-based pastes. The measuring grids 2, 3 are thus printed onto the electrically insulating layer 6 by a printing of the piezoresistive material.

(11) For example, a covering lacquer 11 is provided on these two measuring grids 2, 3 and 102, 103.

(12) The strain gauge 1 produced in this way is comparatively inexpensive and because of its compact embodiment, can also supply measurement data that can be used to robustly compensate for a temperature disturbance variable, for example by means of a bridge circuit.

(13) As is also clear from FIG. 1, the two measuring grids 2, 3 have orientations that are different from each other—in the instance shown, these measuring grids 2, 3 are oriented at right angles. As a result, the second measuring grid 3 functions as a passive measuring grid when there is mechanical strain in the orientation direction O of the first measuring grid 2. The two measuring grids 2, 3 consist of the same piezoresistive material and preferably have the same nominal resistance R0 [Ω]. Consequently, the second mechanically unstrained measuring grid 3 can be used for the temperature compensation of the strain gauge of the first measuring grid 2—for example in that the two measuring grids 2, 3 are provided in the same half-bridge branch of a half-bridge.

(14) The measuring grid 2 consists of four meandering grid sections 2.1, 2.2, 2.3, and 2.4, which are electrically connected in series. It is thus possible to achieve a particularly high sensitivity of the first measuring grid 2 to mechanical strains in the orientation direction O.

(15) The measuring grid 3 is composed of four meandering grid sections 3.1, 3.2, 3.3, and 3.4, which are electrically connected in series. Because a grid section 2.2 of the first measuring grid 2 is positioned between grid sections 3.1 and 3.2 of the second measuring grid 3, a virtually identical temperature influence on the two measuring grids 2 and 3 is established—which makes it possible to largely minimize the influence of the temperature disturbance variable on the measurement result by using measuring grids 2 and 3 in a joint half-bridge, not shown. The latter is achieved in a particularly advantageous way since the grid sections 2.1, 2.2, 2.3, 2.4 and 3.1, 3.2, 3.3, 3.4 are positioned next to one another in alternating fashion and are connected to one another, as shown in FIG. 1.

(16) It is also clear from FIG. 1 that the grid sections 2.1, 2.2, 2.3, and 2.4 of the first measuring grid 2 each have two meandering rows 7, 8 extending next to each other. In addition, all of the grid lengths 12.1, 12.2, 12.3, 12.4 of the first grid sections 2.1, 2.2, 2.3, 2.4 are essentially the same length as all of the grid widths b3.1, b3.2, b3.3, b3.4 of the second grid sections 3.1, 3.2, 3.3, 3.4—making it possible to meet preferred requirements of keeping the two measuring grids 2, 3 at the same temperature level.

(17) Furthermore, the grid sections 2.1, 2.2, 2.3, 2.4 and 3.1, 3.2, 3.3, 3.4 of the respective measuring grids 2, 3 are identically embodied and thus have the same shape, which simplifies the design of the strain gauge 1.

(18) FIG. 2 shows a strain gauge 100 according to a second exemplary embodiment. This strain gauge 100 has a first measuring grid 102 and a second measuring grid 103, which are positioned one inside the other and whose shapes mesh with each other.

(19) The first measuring grid 102 takes shape between the two connections 120.1 and 120.2 and the second measuring grid 103 takes shape between the two electrical connections 130.1 and 130.2. The two measuring grids 102, 103 are positioned in a common plane 9—which can, for example, be a sheet 6 or the like that is coated with a primer or an undercoat serving as an electrical insulation 5, as already described above in connection with the first exemplary embodiment.

(20) According to the invention, the two measuring grids 102, 103 are printed onto the substrate 4, to be precise onto the electrically insulating layer 6 of the substrate 4, which substrate 4 also has a metallic layer 5. The structure of this multi-layer substrate 4 is identical to the first exemplary embodiment and can be inferred from FIG. 1a.

(21) As a result, the two measuring grids 102, 103 can be provided close to one another without short-circuiting. Piezoresistive materials are used for the printing, for example a silver-based paste for the first measuring grid 102 and a graphite-based paste for the second measuring grid 103. The measuring grids 102, 103 are thus printed onto the electrically insulating layer 6 by a printing of the piezoresistive material.

(22) The strain gauge 100 produced in this way can be produced relatively inexpensively and because of its compact embodiment, also has a particularly uniform temperature load of the two measuring grids. Numerical compensation methods can thus robustly remove the temperature disturbance variable from the measurement results of the strain gauge 100.

(23) According to FIG. 2, the first and second measuring grids 102, 103 are oriented identically so that these two measuring grids 102, 103, as active measuring grids, record measurement data in the event of a mechanical strain in the same orientation direction O. The two measuring grids are therefore subject to the same temperature disturbance variable and the same strain. For the compensation of the temperature disturbance variable, the piezoresistive materials of the measuring grids 102, 103 have temperature coefficients (α2, α3) that are different from each other and strain factors (k factors: k1, k2) that are different from each other. The temperature influence in the measurement result can be compensated for by means of these differences.

(24) For a numerical compensation of the temperature disturbance variable, the resistances R.sub.102 and R.sub.103 of the measuring grids 102 and 103 are measured with a suitable method, in the simplest case by means of a resistance measuring device.

(25) For each of the measuring grids, its resistance, disregarding the higher-order dependencies on temperature and strain, can be formally described by
R(ε,T)=R.sub.T.sub.0(1+kε+α.sub.1(T−T.sub.0)).

(26) In this equation, R.sub.T.sub.0 is the nominal resistance of the respective measuring grid without strain at a reference temperature T.sub.0, k is the k factor, α is the temperature coefficient, ε is the strain, and T is the temperature of the measuring grid. Applied to the measuring grids 102 and 103, this yields an equation system consisting of two equations and the two unknown variables of temperature and strain:
R.sub.102(ε,T)=R.sub.102,T.sub.0(1+k.sub.1ε+α.sub.1(T−T.sub.0))
R.sub.103(ε,T)=R.sub.103,T.sub.0(1+k.sub.2ε+α.sub.2(T−T.sub.0))

(27) By solving this equation system, it is possible to calculate the overall temperature and strain of the measuring grids 102 and 103.

(28) This achieves a strain gauge 100 with exact measurement data.

(29) As can also be inferred from FIG. 2, the first and second measuring grids 102, 103 each have a single meandering grid section 102.1, 103.1. These grid sections 102.1, 103.1 are positioned one inside the other and are identically shaped, as a result of which the two measuring grids 102, 103 extend in a double meander.