Abstract
A resistor arrangement for measuring current strength having connection elements and a resistor element between the connection elements. The connection elements and the resistor element are arranged in a plane and in a row such that the arrangement is strip-shaped and has its smallest spatial extent perpendicular to the current direction. The resistor element has two contact sides and the connection elements each have a contact face connected to the contact sides. When current flows through the arrangement, current flow lines are formed which are deflected at at least one of the contact sides by an angle of at least 5° at the transition from the connection element to the resistor element.
Claims
1. A resistor arrangement for measuring the strength of an electric current flowing through the resistor arrangement, the resistor arrangement comprising at least two strip- or plate-shaped connection elements for connecting the resistor arrangement to an external circuit and at least one strip- or plate-shaped resistor element arranged between the connection elements with respect to the direction of the current, the connection elements and the resistor element for forming the resistor arrangement being arranged in a plane next to each other and in a row with respect to each other in such a way that the resistor arrangement has the form of a strip and has its smallest spatial extent in a direction oriented perpendicular to the direction of the electric current, the at least one resistor element consisting of a material of which the electrical resistivity at room temperature is greater by at least a factor of 10 than the electrical resistivity of the material of the connection elements, the at least one resistor element having two contact sides parallel to each other, and the connection elements, each having a contact face at which they are connected to one of the contact sides of the at least one resistor element or of a further resistor element and are in electrical contact, wherein the at least one resistor element is arranged in such a way that, when current flows through the resistor arrangement, current flow lines are formed which are deflected at at least one of the contact sides of the resistor element by an angle of at least 5°, averaged over the entire contact face, at the transition from the connection element to the resistor element, this deflection taking place in a plane which is perpendicular to the direction of the smallest spatial extent of the resistor arrangement.
2. The resistors arrangement according to claim 1, wherein the connection elements and the at least one resistor element are arranged in such a way that the current flow lines are deflected by an angle of at least 15° and by at most 60°.
3. The resistor arrangement according to claim 1, wherein the at least one resistor element is arranged in such a way that, when current flows through the resistor arrangement, current flow lines are formed which are deflected at both contact sides of the resistor element by the same angle, averaged over the particular entire contact face, but in mutually opposite directions, at the transition from the particular connection element to the resistor element.
4. The resistor arrangement according to claim 1, whereinthe resistor arrangement has, in the plane which is perpendicular to the direction of the smallest spatial extent of the resistor arrangement, a base area which corresponds substantially to a parallelogram, the parallelogram having a first and a second longitudinal side which are parallel to the direction of the current in the connection elements, and the contact sides of the at least one resistor element form an angle of at least 25° and at most 85° with the longitudinal sides of the parallelogram.
5. The resistor arrangement according to claim 4, wherein on at least one of the connection elements there is provided at least one voltage tap positioned on an area enclosed by a right-angled triangle, the hypotenuse of which comprises or is a contact side of the resistor element, the first leg of which is a portion of the first longitudinal side of the parallelogram, and the second leg of which is formed by a perpendicular dropped onto the first longitudinal side of the parallelogram from the point of intersection of the hypotenuse with the second longitudinal side of the parallelogram.
6. The resistor arrangement according to claim 5, wherein the voltage tap is positioned on an area enclosed by a right-angled triangle, the hypotenuse of which comprises or is a portion of a contact side of the resistor element, the first leg of which is a portion of the first longitudinal side of the parallelogram, and the second leg of which is formed by a perpendicular dropped onto the first longitudinal side of the parallelogram from a point of the hypotenuse located centrally between the two longitudinal sides of the parallelogram.
7. The resistor arrangement according to claim 5, wherein at least one voltage tap is present on each of the two connection elements, and at least two voltage taps are arranged point-symmetrically with respect to one another, the center of symmetry being defined by a point which is equidistant from both longitudinal sides of the parallelogram and which lies on an imaginary line running equidistantly between the two contact sides, of the resistor element.
8. The resistor arrangement according to claim 1, wherein the connection elements have means for connecting the resistor arrangement to an external circuit, so that a main current direction in the resistor arrangement is defined by these means, and in that the contact sides of the resistor element form an angle of at most 85° with the main current direction.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Exemplary embodiments of the invention are explained in more detail with reference to the schematic drawings, in which:
[0027] FIG. 1 shows a resistor arrangement known from the prior art;
[0028] FIG. 2 shows schematically the current lines in the resistor arrangement according to FIG. 1;
[0029] FIG. 3 shows schematically the equipotential lines in the resistor arrangement according to FIG. 1;
[0030] FIG. 4 shows a resistor arrangement with obliquely positioned resistor element;
[0031] FIG. 5 shows schematically the current lines in the resistor arrangement according to FIG. 4;
[0032] FIG. 6 shows schematically the equipotential lines in the resistor arrangement according to FIG. 4;
[0033] FIG. 7 shows a resistor arrangement with obliquely positioned resistor element and the region for voltage taps;
[0034] FIG. 8 shows a resistor arrangement with obliquely positioned resistor element and a preferred region for voltage taps;
[0035] FIG. 9 shows a resistor arrangement with obliquely positioned resistor element and a preferred region for voltage taps;
[0036] FIG. 10 shows a comparison graph with measurement data; and
[0037] FIG. 11 shows a graph with simulation results.
[0038] Corresponding parts are provided with the same reference signs in all figures.
DETAILED DESCRIPTION
[0039] FIG. 1 shows a schematic oblique view of a resistor arrangement 1 known from the prior art. The resistor arrangement 1 has two connection elements 2, 2′ and a resistor element 3 arranged between these connection elements 2, 2′. Both connection elements 2, 2′ each have a hole 7, 7′ by means of which the resistor arrangement 1 can be connected to an external circuit. The resistor element 3 has two contact sides 31, 32, at which it is electrically conductively connected to a corresponding connection element 2, 2′. A voltage tap 6, 6′ is provided on each of the connection elements 2, 2′. When current flows through the resistor arrangement 1, the voltage dropping across the resistor element 3 can be measured via these voltage taps 6, 6′. Because the voltage taps 6, 6′ are not positioned exactly at the contact lines between resistor element 3 and each connection element 2, 2′, the voltage signal also contains contributions caused by the voltage drop in the connection elements 2, 2′.
[0040] FIG. 2 shows a plan view of the resistor element 1 according to FIG. 1. The resistor arrangement 1 has a base area in the form of a rectangle with two longitudinal sides 51, 52 parallel to each other. The resistor element 3 is arranged so that its two contact sides 31, 32 are perpendicular to the two longitudinal sides 51, 52 of the rectangle. The current flow lines 4 representing the path of the current through the resistor arrangement 1 are shown schematically by dash-dot arrows. The current flow lines 4 run parallel to the two longitudinal sides 51, 52 of the resistor arrangement both in the connection elements 2, 2′ and in the resistor element 3. The current flow lines 4 are perpendicular to the contact faces 21, 21′ of the two connection elements 2, 2′. When the current passes through the contact faces 21, 21′, i.e. at the transition from one connection element 2, 2′ to the resistor element 3 in each case, the current does not change its direction. The current flow lines 4 are not deflected.
[0041] FIG. 3 schematically shows the equipotential lines 41 that result when current flows through the resistor arrangement 1 according to FIG. 1 and FIG. 2. The equipotential lines 41 run both in the connection elements 2, 2′ and in the resistor element 3 parallel to the contact faces 31, 32 of the resistor element 3 and perpendicular to the longitudinal sides 51, 52 of the resistor arrangement 1. Consequently, the equipotential lines 41 in the connection elements 2, 2′ do not intersect the contact faces 31, 32 of the resistor element 3. In the resistor element 3, the equipotential lines 41 are significantly denser than in the connection elements 2, 2′ due to the greater resistance. If the temperature of the resistor arrangement 1 changes, the equipotential lines 41 in the connection elements 2, 2′ shift predominantly because the resistivity of the material of the connection elements 2, 2′ is dependent more strongly on the temperature than the resistivity of the material of the resistor element 3. A changed voltage is therefore detected via the two voltage taps 6, 6′ for the same current strength.
[0042] FIG. 4 schematically shows an oblique view of a resistor arrangement 1 in which the resistor element 3 is arranged obliquely between the two connection elements 2, 2′. The resistor element 3 has two contact sides 31, 32 at which it is electrically conductively connected to respective connection elements 2, 2′. Both connection elements 2, 2′ each have a hole 7, 7′ by means of which the resistor arrangement 1 can be connected to an external circuit. A main current direction can be defined through these bores 7, 7′ by mentally connecting the respective centers of the two bores by a line. The contact sides 31, 32 of the resistor element 3 are inclined with respect to this main current direction. A voltage tap 6, 6′ is provided on each of the connection elements 2, 2′. As in the prior art resistor arrangement 1, the voltage taps 6, 6′ are not positioned exactly at the contact line between resistor element 3 and each connection element 2, 2′, but at a distance from the resistor element 3.
[0043] FIG. 5 shows a plan view of the resistor element 1 according to FIG. 4. The resistor arrangement 1 has a base area in the form of a rectangle with two parallel longitudinal sides 51, 52. The resistor element 3 is arranged so that it forms an angle of approximately 70° with the longitudinal sides 51, 52. The current flow lines 4, which represent the path of the current through the resistor arrangement 1, are shown schematically by dash-dot arrows. The current flow lines 4 run parallel to the two longitudinal sides 51, 52 of the resistor arrangement 1 only in the connection elements 2, 2′. In the resistor element 3, the current flow lines 4 run approximately perpendicular to the contact sides 31, 32 of the resistor element 3 and thus run at an angle with respect to the longitudinal sides 51, 52 of the resistor arrangement 1. When passing through the respective contact faces 21, 21′ of the two connection elements 2, 2′, i.e. at the transition from one connection element 2, 2′ to the resistor element 3 in each case, the current flow lines 4 are thus deflected by approximately 20° in each case. The deflection takes place at the second contact face 21′ in the opposite direction compared to the deflection at the first contact face 21, so that the direction of the current flow lines 4 is the same in both connection elements 2, 2′.
[0044] FIG. 6 schematically shows the equipotential lines 41 that result when current flows through the resistor arrangement 1 according to FIG. 4 and FIG. 5. As in the case of the resistor arrangement known from the prior art, the equipotential lines 41 in the resistor element 3 are significantly denser than in the connection elements 2, 2′ due to the greater resistance. In the two connection elements 2, 2′, the equipotential lines 41 run substantially perpendicularly to both longitudinal sides 51, 52 of the resistor arrangement 1. In the resistor element 3, the equipotential lines 41 run almost parallel to the contact faces 31, 32 of the resistor element 3. They are inclined only by an angle of less than 5° with respect to the contact faces 31, 32. Due to this inclination, equipotential lines 41 running close to the contact faces 31, 32 of the resistor element 3 intersect these contact faces 31, 32 and then continue in the region of the connection elements 2, 2′ as described above. Two voltage taps 6, 6′ are positioned in this region of the two connection elements 2, 2′.
[0045] FIG. 7 schematically shows a plan view of the resistor arrangement 1 according to FIGS. 4 to 6. On both sides of the resistor element 3, two right-angled triangles are drawn in hatched lines, in which the voltage taps 6, 6′ can be positioned to take advantage of the effect described above. The voltage taps 6, 6′ are positioned close to the resistor element 3. The two voltage taps 6, 6′ are arranged point-symmetrically with respect to each other. The center of symmetry is located in the geometric center of the resistor element 3 and is marked by a cross.
[0046] FIG. 8 shows a schematic plan view of the resistor arrangement 1 according to FIGS. 4 to 6. On both sides of the resistor element 3, two right-angled triangles are drawn in hatched lines, in which the voltage taps 6, 6′ can preferably be positioned in order to make particularly good use of the effect described above. The voltage taps 6, 6′ are positioned close to the resistor element 3. The two voltage taps 6, 6′ are arranged point-symmetrically with respect to each other. The center of symmetry is located in the geometric center of the resistor element 3 and is marked by a cross.
[0047] FIG. 9 schematically shows a plan view of a resistor arrangement 1 similar to FIG. 8. In the case of FIG. 9, the voltage taps 6, 6′ are positioned at a clear distance from the resistor element 3 at the outer edge near each of the longitudinal sides 51, 52 of the resistor arrangement 1 in the preferred region.
[0048] FIG. 10 shows a graph in which the measured relative resistance change dR/R in % is plotted as a function of temperature for three resistor arrangements (TCR curve). The resistance was measured using a measuring bridge in the four-wire method. The resistance at 20° C. was used as the reference value in each case. The data series, labeled “perpendicular” was recorded on a resistor arrangement as shown in FIGS. 1 to 3. The voltage taps 6, 6′ were positioned as shown schematically in FIG. 1 and FIG. 3. At a temperature of 100° C., the measured resistance is 0.6% greater than the resistance at 20° C., and at 150° C. the change is about 0.8%. The data series labeled “inclined by 45°” was recorded on a resistor arrangement similar to the resistor arrangement 1 shown in FIGS. 4 to 6, where the resistor element 3 was inclined by 45° with respect to the resistor element 3 of the resistor arrangement 1 shown in FIGS. 1 to 3. The voltage taps 6, 6′ were positioned as shown schematically in FIG. 4 and FIG. 6. At a temperature of 100° C., the measured resistance is 0.2% lower than the resistance at 20° C., and at 150° C. the change is less than −0.5%. The fact that the measured resistance appears to decrease with temperature can be explained by a corresponding shift in the equipotential lines for the resistor arrangement with inclined resistor element. The data series labeled “tilted by 30°” was recorded on a resistor arrangement similar to the resistor arrangement 1 shown in FIGS. 4 to 6, wherein the resistor element 3 was tilted by 30° with respect to the resistor element 3 of the resistor arrangement 1 shown in FIGS. 1 to 3. The voltage taps 6, 6′ were positioned as shown schematically in FIG. 4 and FIG. 6. At a temperature of 100° C., the measured resistance is 0.25% lower than the resistance at 20° C., and at 150° C. the change is slightly more than −0.5%. The comparison of the measured data shows that, for the resistor arrangements with inclined resistor element, especially in the temperature range between 0° C. and 100° C., the change of the measured resistance with temperature is significantly lower than for the resistor arrangement known from the prior art. This proves the advantage of the proposed resistor arrangement.
[0049] FIG. 11 shows a graph with results of simulation calculations. The calculated relative resistance change dR/R as a function of temperature is plotted for two other resistor arrangements. The data series labeled “inclined by 30°” were calculated for a resistor arrangement similar to the resistor arrangement shown in FIGS. 4 to 6, where the resistor element 3 was inclined by 30° with respect to the resistor element 3 of the resistor arrangement 1 shown in FIGS. 1 to 3. The data series labeled “inclined by 15°” were calculated for a resistor arrangement similar to the resistor arrangement 1 shown in FIGS. 4 to 6, where the resistor element 3 was inclined by 15° with respect to the resistor element 3 of the resistor arrangement 1 shown in FIGS. 1 to 3. Two pairs of voltage taps 6, 6′ were simulated for each of the two resistor arrangements: a first pair of voltage taps 6, 6′ was simulated as shown in FIG. 8, i.e. positioned close to the resistor element 3. The corresponding data series are labeled “U: close”. A second pair of voltage taps 6, 6′ was simulated as shown in FIG. 9, i.e. positioned close to one each of the longitudinal sides 51, 52 of the resistor arrangement 1, at a distance from the resistor element 3. The associated data series are marked with the designation “U: far”. In contrast to the experimentally determined data (FIG. 10), the calculated data lie on a straight line, while the data series of the experimentally determined data each have a curvature. This curvature may be due to effects caused by the weld seam.
[0050] For both simulated resistor arrangements, the voltage taps positioned close to the resistor element give almost the same change in resistance with temperature. At 100° C., the relative change with respect to the resistor value at 20° C. is approximately −0.2%. This result agrees well with the measured data. The fact that the simulated resistance appears to decrease with temperature can be explained by a corresponding shift in the equipotential lines.
[0051] The data obtained for voltage taps positioned far from the resistor element in each case show significantly different behavior for the two simulated resistor arrangements: The data obtained on the resistor arrangement with the resistor element inclined by 15° show a positive slope, i.e., an increase in resistance with temperature, and are approximately on par with the measured data obtained experimentally on the prior art resistor arrangement; see FIG. 10. The data obtained on the resistor arrangement with the resistor element inclined by 30° show a negative slope, i.e., an apparent decrease in resistance with temperature. The decrease in this case is greater than the decrease in resistance when the voltage taps are positioned close to the resistor element. Comparison of the data suggests that, for a given slope of the resistor element in combination with a given position of the voltage taps, opposing effects can cancel each other out and thus the voltage measurement is based on an apparent resistance that is practically independent of temperature.
LIST OF REFERENCE SIGNS
[0052] 1 resistor arrangement [0053] 2, 2′ connection element [0054] 21, 21′ contact face [0055] 3 resistor element [0056] 31 contact side [0057] 32 contact side [0058] 4 current flow lines [0059] 41 equipotential lines [0060] 51 longitudinal side [0061] 52 longitudinal side [0062] 6, 6′ voltage tap [0063] 7, 7′ connection means, bore
