Resistor and method for the production thereof

Abstract

The invention concerns a resistor, in particular a low-resistance current measuring resistor, having two connecting parts made of a conductor material and a resistor element made of a resistance material inserted between the connecting parts, the resistance material having a specific thermal force which generates a specific thermoelectric voltage in the event of a temperature difference between the resistor element on the one hand and the connecting parts on the other hand. The invention additionally provides for a compensating element which in operation generates a thermoelectric voltage which at least partially compensates for the thermoelectric voltage generated by the resistor element. Furthermore, the invention includes a corresponding manufacturing process.

Claims

1. A resistor comprising: a) a first connecting part made of a conductor material; b) a second connecting part made of the conductor material; c) a resistor element made of a resistance material, wherein: c1) the resistor element is arranged in the current direction between the first connecting part and the second connecting part and through which the electric current flows; c2) the resistance material has a specific thermal force which generates a specific thermoelectric voltage at a temperature difference between the resistor element on the one hand and the connecting parts on the other hand, and d) further comprising a compensating element which in operation generates a thermoelectric voltage which at least partially compensates the thermoelectric voltage generated by the resistor element e) a first voltage tap which is electrically conductively connected to the first connecting part; f) a second voltage tap which is electrically conductively connected to the second connecting part; g) wherein a voltage measuring circuit can be connencted to the first voltage tap and to the second voltage tap in order to measure the voltage across the resistor element; h) the second voltage tap is arranged on the first connecting part; i) the second voltage tap is electrically insulated from the first connecting part; j) the compensating element is thermally conductively connected to the first connecting part at the second voltage tap; k) the second voltage tap is electrically conductively connected via the compensating element to a contact point on the second connecting part; and l) the compensating element is electrically and thermally conductively connected to the second connecting part at the contact point on the second connecting part.

2. The resistor according to claim 1, wherein the compensating element is inserted into a voltage measuring line which measures the voltage drop across the resistor element.

3. The resistor according to 1, wherein: a) the compensating element is thermally connected in parallel with the resistor element so that the compensating element is exposed to substantially the same temperature differences as the resistor element and therefore generates substantially the same amount of thermoelectric voltage as the resistor element; and b) the compensating element is connected in series with the resistor element in the voltage measuring circuit so that the thermoelectric voltages of the resistor element and of the compensating element at least partially compensate each other.

4. The resistor according to claim 1, further comprising a voltage divider having two resistors, the voltage divider being connected in parallel with the compensating element and forming an external voltage tap with its central tap.

5. The resistor according to claim 1, wherein a printed circuit board, which carries the compensating element, is mounted on the resistor.

6. The resistor according to claim 5, wherein the printed circuit board is multi-layered.

7. The resistor according to claim 5, wherein the printed circuit board is soldered to the resistor.

8. The resistor to claim 1, wherein the compensating element is made of a material which has substantially the same thermal force as the resistance material with a deviation of less than 10%.

9. The resistor according to claim 1, wherein the compensating element also consists of the resistance material of the resistor element.

10. The resistor according to claim 1, wherein: a) the connecting parts are each plate-shaped; and b) the resistor element is plate-shaped.

11. The resistor according to claim 1, wherein: a) the conductor material of the connecting parts is copper or a copper alloy or aluminum; b) the resistance material is a copper-manganese alloy; c) the resistance material of the resistor element has a higher specific electrical resistance than the conductor material of the connecting parts; d) the resistance material of the resistor element has a resistive electrical resistance which is: d1) less than 50.Math.10.sup.7 m, and d2) is greater than 1.Math.10.sup.8 m; and e) the resistor has a resistance value which is: e1) at least 0.1 , and e2) a maximum of 1000 ; and f) the resistor has a resistance value with a temperature coefficient of less than 500 ppm/K.

12. The resistor according to claim 1, wherein the two connecting parts and the resistor element are separated from a composite material strip transversely to the longitudinal direction of the composite material strip and bent.

13. A resistor comprising: a) a first connecting part made of a conductor material; b) a second connecting part made of the conductor material; c) a resistor element made of a resistance material, wherein: c1) the resistor element is arranged in the current direction between the first connecting part and the second connecting part and through which the electric current flows; c2) the resistance material has a specific thermal force which generates a specific thermoelectric voltage at a temperature difference between the resistor element on the one hand and the connecting parts on the other hand; d) further comprising a compensating element which in operation generates a thermoelectric voltage which at least partially compensates the thermoelectric voltage generated by the resistor element; and wherein the compensating element is a composite material plate which consists externally of the conductor material of the connecting parts and centrally of the resistance material of the resistor element.

14. A resistor comprising: a) a first connecting part made of a conductor material; b) a second connecting part made of the conductor material; c) a resistor element made of a resistance material, wherein: c1) the resistor element is arranged in the current direction between the first connecting part and the second connecting part and through which the electric current flows; c2) the resistance material has a specific thermal force which generates a specific thermoelectric voltage at a temperature difference between the resistor element on the one hand and the connecting parts on the other hand; d) further comprising a compensating element which in operation generates a thermoelectric voltage which at least partially compensates the thermoelectric voltage generated by the resistor element; and wherein the compensating element comprises a part of the resistor element which is electrically insulated from the rest of the resistor element.

15. The resistor according to claim 14, wherein the compensating element also comprises a part of the first connecting part which is electrically insulated from the rest of the first connecting part.

16. The resistor according to claim 15, wherein the compensating element is electrically separated from the remainder of the first connecting part and of the resistor element by a separating slit.

17. The resistor according to claim 16, wherein the separating slit is introduced into the resistor by a laser beam or a water jet or by milling.

18. The resistor according to claim 17, wherein the separating slit is at least partially filled with a filling material.

19. The resistor according to claim 18, wherein the filling material is thermally conductive and electrically insulating.

20. A resistor comprising: a) a first connecting part made of a conductor material; b) a second connecting part made of the conductor material; c) a resistor element made of a resistance material, wherein: c1) the resistor element is arranged in the current direction between the first connecting part and the second connecting part and through which the electric current flows; c2) the resistance material has a specific thermal force which generates a specific thermoelectric voltage at a temperature difference between the resistor element on the one hand and the connecting parts on the other hand; d) a compensating element which in operation generates a thermoelectric voltage which at least partially compensates the thermoelectric voltage generated by the resistor element; wherein the compensating element has a reduced thickness with respect to the remainder of the resistor; and wherein the thickness reduction of the compensating element is produced by milling off the resistor in the region of the compensating element.

21. The resistor according to claim 20, wherein the thickness of the compensating element is less than 50% of the thickness of the remainder of the resistor.

Description

(1) Other advantageous further modifications of the invention are indicated in the dependent claims or explained in more detail below together with the description of the preferred embodiments of the invention using the figures. The show:

(2) FIG. 1 shows a schematic representation of a conventional low-resistance current measuring resistor for current measurement according to the four-wire technique,

(3) FIG. 2 an inventive modification of a low resistance current measuring resistor with a compensating element in the form of a wire or ribbon,

(4) FIG. 3 a modification of FIG. 2, where instead of the wire or ribbon a composite material plate is used as a compensating element,

(5) FIG. 4 is a modification of FIG. 2, where the compensating element is machined out of the finished resistor,

(6) FIG. 5 shows a schematic diagram illustrating the principle of the compensating element,

(7) FIG. 6 shows a modification of FIG. 5 with an additional voltage divider to avoid overcompensation of the thermoelectric voltages,

(8) FIG. 7A shows a cross-sectional view through an resistor according to the invention with a printed circuit board carrying the compensating element along the section line A-A in FIG. 7B,

(9) FIG. 7B a top view of the embodiment according to FIG. 7A, and

(10) FIG. 8 is a modification of FIG. 7B.

(11) FIG. 1 shows a schematic representation of a conventional low resistance current measuring resistor 1, as known from EP 0 605 800 A1.

(12) The current measuring resistor 1 first has a first plate-shaped connecting part 2 made of a conductor material (e.g. copper, copper alloy) in order to introduce an electrical current I to be measured into the current measuring resistor 1.

(13) In addition, the current resistor 1 has a plate-shaped second connecting part 3, which also consists of a conductor material (e.g. copper, copper alloy) and serves to conduct the electrical current I to be measured out of the current resistor 1.

(14) A plate-shaped resistor element 4 is also inserted between the two connecting parts 2, 3, which is electrically and mechanically connected to the two adjacent connecting parts 2, 3 by means of weld seams 5, 6. The electrical current I to be measured is therefore fed into the current measuring resistor 1 via the connecting part 2, then flows through resistor element 4 and is finally led out of the current measuring resistor 1 again via the connecting part 3.

(15) A voltage drops over the resistor element 4 during operation, which is proportional to the electrical current I to be measured according to Ohm's law, allowing current measurement according to the well-known four-wire technique.

(16) For this reason, two voltage taps 7, 8 are located on the two connecting parts 2, 3 in the immediate vicinity of the resistor element 4, each of which is connected to a voltage measuring instrument 11 via a voltage measuring line 9, 10. The electrical voltage measured by the voltage measuring instrument 11 is then a direct measure of the electrical current I flowing through the current measuring resistor in accordance with Ohm's law.

(17) As already mentioned at the beginning, the problem here is that the conductor material of the connecting parts 2, 3 generally has a slightly different thermal force than the resistance material of resistor element 4. As a result, temperature differences between the resistor element 4 on the one hand and the connecting parts 2, 3 on the other hand result in thermoelectric voltages which falsify the voltage measurement by the voltage measuring instrument 11.

(18) This problem is solved by the embodiment according to the invention shown in FIG. 2, which is described below. However, the example shown in FIG. 2 partially corresponds to the conventional current resistor 1 shown in FIG. 1, so that, in order to avoid repetitions, reference is made to the above description, using the same reference signs for corresponding details.

(19) A special feature of this embodiment is that the second voltage tap 8 for the potential measurement on the second connecting part 3 is not located on the second connecting part 3, but on the first connecting part 2, close to the weld seam 5. However, the second voltage tap 8 is electrically isolated from the first connecting part 2, for example by an electrically isolated, thermally coupled solder joint.

(20) The electrical connection between the second voltage tap 8 and the second connecting part 3 is made by a compensating element 12 in the form of a wire or ribbon. The compensating element 12 is electrically connected at one end to the second voltage tap 8. At its opposite end, the wire- or ribbon-shaped compensating element 12 is electrically and thermally connected to a contact point 13 on the second connecting part 3.

(21) As a result of this arrangement, the filamentary compensation element 12 is thermally connected in parallel with the resistor element 4 and is therefore exposed to the same temperature differences as the resistor element 4 during operation. As a result, the filamentary compensating element 12 also generates the same thermoelectric voltage as the resistor element 4, as the resistor element 4 is made of the same resistance material as the filamentary compensating element 12. Thermal contacting is effected, on the one hand, by the second voltage tap 8 and, on the other hand, by the contact point 13.

(22) On the other hand, this design means that the compensating element 12 in the voltage measuring circuit is connected in series with the resistor element 4, so that the thermoelectric voltages of the resistor element on the one hand and of the compensating element 12 on the other hand compensate each other.

(23) FIG. 3 shows a modification of the embodiment according to FIG. 2, so that in order to avoid repetitions, reference is made to the above description, using the same reference signs for corresponding details.

(24) A special feature of this example is that the compensating element 12 is not formed by a wire or a ribbon, but by a composite material plate with a central part 14 of the same resistance material as the resistor element 4 and two outer parts 15, 16 of the same conductor material as the two connecting parts 2, 3.

(25) Otherwise, the operation of this example corresponds to that of the example shown in FIG. 2, so to avoid repetition, please refer to the above description.

(26) FIG. 4 shows a modification of the embodiments according to FIGS. 2 and 3, so that to avoid repetitions, reference is made again to the above description, using the same reference signs for corresponding details.

(27) A special feature of this example is that the compensating element 12 is not subsequently connected to the current measuring resistor 1. Instead, the compensating element 12 is machined out of the finished current resistor 1. For this purpose, a slit 17 is inserted into the current measuring resistor 1, for example by means of a laser beam, a water jet or by milling. The slit 17 separates the compensating element 12 from the rest of the resistor element 4. In addition, the slit 17 also separates the compensating element 12 from the rest of the connecting part 2. The slit 17 thus also surrounds the second voltage tap 8 in the area of the first connecting part 2.

(28) The operation of this example corresponds to the operation of the other examples of the invention described above, so that reference can be made to the above description to avoid repetition.

(29) FIG. 5 shows a schematic equivalent circuit diagram of the embodiments according to FIGS. 2-4.

(30) It should be noted that over-compensation of the thermoelectric voltage may occur under certain circumstances. In order to avoid such overcompensation, the embodiment in FIG. 6 shows that a voltage divider consisting of two resistors R1, R2 is connected in parallel to the compensating element 12, the voltage divider consisting of the resistors R1, R2 having a center tap 18 connected to the voltage measuring instrument 11.

(31) FIGS. 7A and 7B show another embodiment of a current measuring resistor 1 according to the invention. This embodiment also partly corresponds to the embodiments described above, so that reference is made to the above description in order to avoid repetitions, using the same reference signs for corresponding details.

(32) A special feature of this embodiment is that the compensating element 12 is realized as a foil which is arranged on a printed circuit board 19 on the upper side or one of the inner layers of the printed circuit board 19. The printed circuit board 19 is here arranged on the upper side of the current measuring circuit 1 and thermally and electrically connected to the current measuring resistor 1 (preferably soldered, soldering joints 24, 25), as explained below.

(33) Thus the printed circuit board 19 has an electrical through-contact 20, which electrically and thermally connects the compensating element 12 with the second connecting part 3.

(34) On the opposite end, the compensating element 12 is connected to a copper track 21, which electrically conductively connects the compensating element 12 to the second voltage tap 8.

(35) The first voltage tap 7, on the other hand, is connected via a further copper track 22 to an electrical through-contact 23, which makes an electrical contact with the first connecting part 2. This design ensures that the compensating element 12 is thermally connected in parallel with the resistor element 4, while the compensating element 12 in the voltage measuring circuit is connected in series with the resistor element 4, so that the thermoelectric voltages of the resistor element on the one hand and of the compensating element 12 on the other compensate each other.

(36) It should be mentioned here that thermal couplings 26, 27, consisting of suitably shaped Cu inner layers, are also provided, which thermally connect the ends of the compensating element 12 better with the connecting part 2 or the connecting part 3.

(37) FIG. 8 shows a modification of FIG. 7B with the voltage divider from resistors R1 and R2 already shown in FIG. 6. With regard to the functioning of this variation, reference can therefore be made to the above description of FIG. 6.

(38) The invention is not limited to the preferred embodiments described above. Rather, a large number of variants and modifications are possible which also make use of the invention idea and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and the features of the dependent claims independently of the claims referred to in each case and also without the features of the main claim.

LIST OF REFERENCE SIGNS

(39) 1 Current measuring resistor 2 First connecting part 3 Second connecting part 4 Resistor element 5 Weld seam 6 Weld seam 7 First voltage tap 8 Second voltage tap 9 Voltage measuring line 10 Voltage measuring line 11 Voltage measuring instrument 12 Compensating element 13 Contact point of the compensating element on the second connecting part 14 Middle part of the compensating element 15 Outdoor part of the compensating element 16 Outdoor part of the compensating element 17 Slit 18 Center tap of the voltage divider 19 Printed circuit board 20 Electrical through-connection 21 Copper track 22 Copper track 23 Electrical through-connection 24 Solder joint 25 Solder joint 26 Cu inner layer for better thermal coupling 27 Cu inner layer for better thermal coupling 28 Contact point I Current R1 Voltage divider resistor

(40) While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.