CURRENT MEASURING DEVICE WITH REDUNDANT CURRENT MEASUREMENT

Description

[0001] The invention relates to a current measuring device for redundantly measuring an electrical current.

[0002] EP 0 605 800 A1 discloses a current measuring device comprising a low-resistance current measuring resistor ("shunt"), whereby the electrical current to be measured is measured using the four-wire technique. The electrical current to be measured is passed through the low-resistance current measuring resistor, and the voltage drop across the low-resistance current measuring resistor is measured. According to Ohm's law, the voltage drop across the low-resistance current measuring resistor provides a measure of the electrical current to be measured.

[0003] Furthermore, it is known from the prior art to use Hall sensors for current measurement, which detect the magnetic field generated by the electrical current to be measured.

[0004] Furthermore, EP 2 511 714 A2 discloses a current measuring device that combines both measuring principles and features both a low-resistance current measuring resistor ("shunt") and a Hall sensor, enabling redundant current measurement. In this known current measuring device, the electrical current to be measured is passed through the low-resistance current measuring resistor, with the Hall sensor being arranged above the low-resistance current measuring resistor and measuring the same current. These known current measuring devices can measure currents up to ±1000 A, with a resolution of 1 to 5 A and a tolerance of ±10%.

[0005] Hall sensors with an integrated conductor are also known, with the current to be measured flowing through the integrated conductor. Such Hall sensors have a resolution of approximately 0.5 to 1 A with a tolerance of ±1%.

[0006] The disadvantage of these current measuring devices, however, is that the measuring range of the entire current measuring device is limited to ±1000 A and has a low resolution and high tolerance. Chip sensors have a significantly lower measuring range, but in return, better resolution and smaller tolerance.

[0007] Furthermore, current measuring devices according to the preamble of claim 1 are known from DE 10 2011 088 893 A1 and US 2020 / 0300917 A1. However, these known current measuring devices are not yet optimal.

[0008] Furthermore, with regard to the general technical background of the invention, reference should be made to US 5,841,272, US 2011 / 0221429 A1, US 2015 / 088438 A1 and US 2015 / 309080 A1.

[0009] Finally, DE 10 2012 212 367 A1 discloses a current measuring device according to the preamble of claim 1. However, this known current measuring device is not entirely satisfactory.

[0010] The invention is therefore based on the object of creating a correspondingly improved current measuring device.

[0011] This object is achieved by a current measuring device according to the invention according to the main claim.

[0012] The current measuring device according to the invention, in accordance with the prior art, initially comprises a low-ohm current measuring resistor to enable current measurement according to the four-wire technique, as known, for example, from EP 0 605 800 A1. The electrical current is passed through the low-ohm current measuring resistor, and the voltage drop across the low-ohm current measuring resistor is measured. The measured voltage then forms a measure of the electrical current according to Ohm's law.

[0013] Furthermore, in accordance with the prior art according to EP 2 511 714 A2, the current measuring device according to the invention also comprises a magnetic field sensor for redundant current measurement, i.e. the magnetic field sensor measures the electrical current according to a measuring principle other than the four-wire technique. For example, the magnetic field sensor can be a Hall sensor, as is known per se. However, it is alternatively also possible for the magnetic field sensor to be a magnetoresistive magnetic field sensor, such as a so-called GMR sensor (GMR: Giant Magnetoresistance), as is also known per se from the prior art. The invention is therefore not limited to a specific type of magnetic field sensor.

[0014] The current measuring device according to the invention is distinguished from the prior art in that the electrical current to be measured is divided in the measuring device into a main current path with a main current and a secondary current path with a secondary current, wherein the main current path and the secondary current path together form a parallel circuit.

[0015] The low-ohm current measuring resistor is arranged in the main current path and is traversed by the main current, so that the main current can be measured according to the four-wire technique.

[0016] The magnetic field sensor, on the other hand, is located in the bypass current path and measures the bypass current according to a different measuring principle, which again enables redundant current measurement.

[0017] In contrast to the known current measuring device according to EP 2 511 714 A2, the low-ohm current measuring resistor on the one hand and the magnetic field sensor on the other hand do not measure the same current, but rather different currents, namely the main current on the one hand and the auxiliary current on the other. This has the advantage that the measuring range of the entire current measuring device is not restricted by the limited measuring range of the magnetic field sensor, since the magnetic field sensor measures a different current than the low-ohm current measuring resistor.

[0018] According to the invention, the parallel circuit of the main current path on the one hand and the secondary current path on the other hand is designed such that the main current through the main current path is substantially greater than the secondary current in the secondary current path, namely by a factor of at least 10, 100, 200, 500 or even 1000 greater than the secondary current.

[0019] The secondary current path therefore preferably has an electrical resistance value that is significantly greater than the resistance value of the main current path. For example, the resistance value of the secondary current path can be a factor of 10, 100, 200, 500, or 1000 greater than the resistance value of the main current path.

[0020] In absolute terms, the resistance value of the main current path can be in the range of 1 µΩ, 10 µΩ, 20 µΩ, 50 µΩ, 100 µΩ, 200 µΩ or 500 µΩ, whereby deviations of a maximum of ±50%, ±20%, ±10%, ±5%, ±2% or ±1% are possible within this range definition.

[0021] The resistance value of the secondary current path, on the other hand, is in absolute terms, for example, in the range of 1 mΩ, 2 mΩ, 5 mΩ, 10 mΩ, 20 mΩ, 50 mΩ or 100 mΩ, whereby deviations of a maximum of plus ±50%, ±20%, ±10%, ±5%, ±2% or ±1% are possible within this range definition.

[0022] The low-ohm current measuring resistor preferably has a larger current measuring range than the magnetic field sensor. The current measuring range of the magnetic field sensor is therefore generally significantly smaller than the current measuring range of the low-ohm current measuring resistor. However, this is not a problem with the current measuring device according to the invention because the magnetic field sensor, on the one hand, and the low-ohm current measuring resistor, on the other hand, measure different currents, so that the smaller current measuring range of the magnetic field sensor does not limit the overall current measuring range of the current measuring device according to the invention.

[0023] Furthermore, a compensating resistor can additionally be arranged in the secondary current path with the magnetic field sensor in order to reduce the temperature dependence of the measurement. The idea of ​​using a compensating resistor to reduce the temperature dependence of the measurement is basically known from DE 10 2016 014 130 B3, so that a detailed description of the functioning of the compensating resistor can be omitted. At this point, it should only be mentioned that the main current path and the secondary current path in the current measuring device according to the invention each contain conductor material (e.g. copper) with a specific first temperature coefficient with regard to the resistance value and resistance material with a specific second temperature coefficient with regard to the resistance value, wherein the first temperature coefficient of the conductor material is significantly greater than the second temperature coefficient of the resistance material.The resistance of the conductor material is therefore significantly more temperature-dependent than the resistance of the resistor material. For example, the two temperature coefficients of the conductor material and the resistor material can differ by a factor of at least 10, 20, 50, 100, or 200. The compensating resistor in the secondary current path, on the other hand, consists of a resistor material that has a significantly lower temperature coefficient than the conductor material. The compensating resistor is dimensioned in terms of its resistance value so that the temperature dependence of the resistance of the conductor material is at least partially compensated. For example, the first temperature coefficient of the conductor material can be in the range of 1,000-10,000 ppm / K or 3,600-4,000 ppm / K, while the second temperature coefficient of the resistance material can be in the range of 0 to ±100 ppm / K, 0 to ±50 ppm / K, 0 to ±20 ppm / K, or 0 to ±10 ppm / K.

[0024] To compensate for temperature dependence, the main current path and the secondary current path preferably have the same resistance ratio between the resistance value of the conductor material and the resistance value of the resistance material of the low-ohm current measuring resistor or the compensating resistor. Preferably, the deviation of the resistance ratio between the main current path and the secondary current path is less than ±20%, ±10%, ±5%, or ±2%.

[0025] The low-ohm current measuring resistor in the current measuring device according to the invention can be designed in a conventional manner. Preferably, the low-ohm current measuring resistor is plate-shaped with plate-shaped current connection parts and a plate-shaped resistance element, wherein the plate-shaped resistance element is arranged between the two plate-shaped current connection parts in the direction of current flow, as is already known from EP 0 605 800 A1.

[0026] Furthermore, within the scope of the invention, it is possible for at least one of the two plate-shaped current connection parts and / or the resistance element of the low-ohm current measuring resistor to have a notch on one or both sides for trimming the resistance value. Furthermore, the plate-shaped connection parts can also have a notch in the center for trimming the resistance value.

[0027] It has already been mentioned above that, in current measurement using the four-wire technique, the voltage drop across the low-ohm current measuring resistor is, according to Ohm's law, a measure of the electrical current flowing through the low-ohm current measuring resistor. The current measuring device according to the invention therefore has at least one pair of voltage measuring contacts that measure the voltage drop across the low-ohm current measuring resistor.

[0028] Preferably, several pairs of voltage measuring contacts are provided, distributed transversely to the current flow direction, in order to be able to compensate for inhomogeneities in the current density in the current measuring resistor. The idea of ​​measuring the voltage drop across the low-ohm current measuring resistor using several pairs of voltage measuring contacts is known per se from WO 2014 / 161624 A1 and therefore need not be described in detail.

[0029] Furthermore, within the scope of the invention, there is also the possibility that several pairs of voltage measuring contacts are arranged one behind the other in the direction of current flow on the low-ohm current measuring resistor, as described in DE 10 2020 111 634.9.

[0030] In addition, incisions can be arranged centrally in the current connection parts of the low-ohm current measuring resistor. These incisions, also referred to as current shadows, each surround one of the voltage measuring contacts to influence the current density in the current connection parts. Such current shadows are already known from the prior art and are described, for example, in DE 10 2020 111 634.9.

[0031] In the preferred embodiment of the invention, a circuit board is arranged on the plate-shaped current measuring resistor, which also carries the magnetic field sensor (e.g., Hall sensor, GMR sensor). The magnetic field sensor and the current measuring resistor are preferably located on opposite sides of the circuit board.

[0032] The circuit board is preferably permanently connected to the low-resistance current measuring resistor and has vias to enable contact between the two current connection parts of the low-resistance current measuring resistor. The vias preferably contact the current connection parts downstream of the resistance element of the low-resistance current measuring resistor and downstream of the resistance element of the low-resistance current measuring resistor.

[0033] The secondary current path preferably runs on or in the circuit board, while the main current path runs through the low-ohm current measuring resistor.

[0034] The circuit board may also carry an evaluation circuit that measures the voltage drop across the resistance element of the low-ohm current measuring resistor, the output signal of the magnetic field sensor and / or the voltage drop across the compensating resistor in the secondary current path.

[0035] Furthermore, the circuit board can have an interface to output the output signal of the magnetic field sensor and / or the voltage measurement value of the voltage across the resistance element of the low-ohm current measuring resistor.

[0036] In the preferred embodiment of the invention, the circuit board has several parallel layers. The compensating resistor is preferably arranged on the topmost layer of the circuit board. The secondary current path with the secondary current is preferably initially divided between several layers of the circuit board upstream of the compensating resistor and is only combined shortly before the compensating resistor, so that the entire secondary current flows through the compensating resistor. Downstream of the compensating resistor, the secondary current path is then divided again among the various layers of the circuit board. This division of the secondary current path across several layers of the circuit board offers the advantage that the resistance value in the secondary current path is relatively small.

[0037] It should also be noted that the current measuring device typically has a high-voltage and a low-voltage range. The low-ohm current measuring resistor is located entirely within the high-voltage range, while the magnetic field sensor separates the high-voltage range from the low-voltage range. Thus, the magnetic field sensor has a low-voltage side, which serves, for example, to output signals and supply a supply voltage. Furthermore, the magnetic field sensor has a high-voltage side that encloses the secondary current path. The magnetic field sensor contains insulation that separates the high-voltage range from the low-voltage range.

[0038] In general, it should be mentioned that the current measuring device according to the invention can have a current measuring range that extends to at least 0.5 kA, 1 kA, 2 kA, 5 kA, 10 kA or 20 kA.

[0039] Furthermore, it should be mentioned that the current measuring device according to the invention preferably has a high dielectric strength on the input side, which can, for example, reach up to an operating voltage of at least 100 V, 500 V or 1 kV.

[0040] The above-mentioned conductor material of the power connection parts is preferably copper or a copper alloy or aluminum or an aluminum alloy.

[0041] The resistance material of the resistance element of the low-ohm current-sensing resistor can be, for example, a copper alloy, in particular a copper-manganese-nickel alloy. For example, this can be CuMn12Ni2, Cu84Ni4Mn12, or Cu65Mn25Ni10. Alternatively, the resistance material can be a copper-manganese-tin alloy, such as CuMn7Sn2.3. Furthermore, it is also possible for the resistance material to be a copper-chromium alloy. Finally, the resistance material can also be a nickel alloy, such as NiCr or CuNi.

[0042] Furthermore, it should be mentioned that the conductor material of the current connection parts of the low-ohm current measuring resistor preferably has a lower specific electrical resistance than the resistance material of the resistance element.

[0043] The conductor material of the current connection parts of the low-ohm current measuring resistor can, for example, have a specific electrical resistance of less than 20 µΩcm, 10 µΩcm, 5 µΩcm or 2 µΩcm.

[0044] The resistance material of the resistance element of the low-ohm current measuring resistor, on the other hand, preferably has a specific electrical resistance of less than 1000 µΩcm, 500 µΩcm, 250 µΩcm, 100 µΩcm or 50 µΩcm.

[0045] In general, it should be mentioned that the low-ohm current measuring resistor preferably has a resistance value of at most 500 mΩ, 200 mΩ, 100 mΩ, 50 mΩ, 20 mΩ, 10 mΩ, 5 mΩ, 2 mΩ or 1 mΩ.

[0046] Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to the figures. Figure 1shows a perspective view of a current measuring device according to the invention with a low-ohm current measuring resistor and a Hall sensor. Figure 2 shows a top view of the current measuring device according to Figure 1 . Figure 3 shows a top view of the current measuring resistor according to the Figures 1 and 2 . Figure 4 shows an equivalent circuit diagram of the current measuring device according to the Figures 1-3 . Figure 5 shows a variation of Figure 3 . Figure 6 shows a further variation of Figure 3 . Figure 7 shows the temperature dependence of the current measurement in the main current path with and without compensating resistor. Figure 8 shows the temperature dependence of the current measurement in the secondary current path with and without compensating resistor.

[0047] The Figures 1-4show various representations of a current measuring device according to the invention for measuring an electric current I, wherein the current measurement is carried out redundantly, namely on the one hand according to the known four-wire technology and on the other hand by a magnetic field measurement.

[0048] For current measurement according to the four-wire technique, the current measuring device has a low-ohm current measuring resistor 1, which consists of two plate-shaped current connection parts 2, 3 and a low-ohm resistance element 4, which is also plate-shaped and is located between the two current connection parts 2, 3 in the direction of current flow. The current connection part 2 serves to introduce the electrical current I to be measured into the current measuring resistor 1, while the current connection part 3 serves to discharge the electrical current I to be measured from the current measuring resistor 1, as is known per se from the prior art.

[0049] In the two power connection parts 2, 3 there are cylindrical holes 5, 6, which enable, for example, a mechanical connection of busbars.

[0050] On the top side of the current measuring resistor 1 is a multilayer printed circuit board 7, which is connected to the connection parts 2 and 3 by means of two vias 8 and 9. The via 8 contacts the current connection part 2, while the via 9 contacts the other current connection part 3.

[0051] On the top side of the circuit board 7 there are conductor tracks 10, 11, 12 and a compensating resistor 13.

[0052] The electrical current I to be measured is divided in the current measuring device according to the invention into a main current I1 and a secondary current I2. The main current I1 flows in the current measuring resistor 1 from the current connection part 2 through the resistance element 4 to the current connection part 3. The secondary current I2, on the other hand, flows from the current connection part 2 through the via 8 via the conductor track 10, through the compensating resistor 13, through the conductor track 11, through a Hall sensor 14, through the conductor track 12, through the via 9 and back into the current connection part 3, where the secondary current I2 recombines with the main current I1 to form the current I.

[0053] For voltage measurement according to the four-wire technique, several pairs of voltage measuring contacts 15-20 are provided (cf. Fig. 3), wherein each of the pairs of voltage measuring contacts 15, 16, 17, 18 or 19, 20 measures the voltage at the current connection part 2 on the one hand and at the current connection part 3 on the other. The pairs of voltage measuring contacts 15-20 are arranged distributed transversely to the current flow direction in order to be able to compensate for inhomogeneities in the current density in the current measuring resistor 1 by measurement, as described in WO 2014 / 161624 A1.

[0054] The voltages at the voltage measuring contacts 15-20 can be measured, for example, by a measuring circuit that can be integrated into the Hall sensor 14. Alternatively, however, it is also possible to arrange a separate measuring circuit on the circuit board 7 that measures the voltage drop across the resistance element 4 of the low-ohm current measuring resistor 1.

[0055] Furthermore, it should be mentioned that the current measuring resistor 1 has several notches 21-24 on the sides of the two current connection parts 2, 3, which in combination with the compensating resistor serve for temperature compensation.

[0056] The compensating resistor 13 in the secondary current path has the purpose of reducing the temperature dependence of the measurement, as is already known from the patent DE 10 2016 014 130 B3.

[0057] It should also be noted that the Hall sensor 14 measures the auxiliary current I2, which flows through the Hall sensor 14 for this purpose. On its measuring side, the Hall sensor 14 is therefore exposed to the high voltage in the auxiliary current path. Furthermore, the Hall sensor 14 also has a low-voltage side, which serves to output a measurement signal and supply a supply voltage. The Hall sensor 14 thus separates the high-voltage side from the low-voltage side and has integrated insulation for this purpose.

[0058] The current measuring device according to the invention enables redundant current measurement using different measuring principles, namely, on the one hand, a four-wire measurement using the low-ohm current measuring resistor 1 and, on the other hand, a magnetic field measurement using the Hall sensor 14.

[0059] It should be noted that the auxiliary current I2 is significantly smaller than the main current I1 flowing through the low-ohm current measuring resistor 1. The Hall sensor 14 can therefore have a significantly smaller current measuring range, which is advantageous. Hall sensors with an integrated conductor often have a small current measuring range of 5 A to 50 A.

[0060] In the following, the equivalent circuit diagram according to Figure 4 which shows a main current path 25 and a secondary current path 26, wherein the main current path 25 and the secondary current path 26 form a parallel circuit.

[0061] Essentially, only the low-ohm current measuring resistor 1 is arranged in the main current path 25, which is represented in the equivalent circuit diagram by a series connection of an ohmic resistor R Shunt and an ohmic resistor R CU1 . The resistor R Shunt represents the ohmic resistance of the low-ohmic resistance element 4. The ohmic resistor R CU1 , on the other hand, represents the resistance of the two current connection parts 2, 3.

[0062] The Hall sensor 14 is arranged in the auxiliary current path 26. Furthermore, the auxiliary current path 26 contains the compensating resistor 13, which is represented by an ohmic resistor RP and an ohmic resistor R CU2 . The resistor RP corresponds to the resistance element of the compensating resistor 13, while the resistor R CU2 corresponds to the two connection parts of the compensating resistor 13. Furthermore, the auxiliary current path 16 also contains a resistor R CU0, which represents the resistance value of the vias 8, 9 and the conductor tracks 10-12.

[0063] During operation, an evaluation circuit measures the voltage drop across the resistance element 4 of the low-ohm current measuring resistor 1. For this purpose, the equivalent circuit diagram according to Figure 4 Voltage measuring contacts U2 / U3, U2A / U3A are shown, which correspond to the voltage measuring contacts 15-20 in Figure 3 are equivalent to.

[0064] On the other hand, the evaluation circuit detects the output voltage U HALL measured by the Hall sensor 14.

[0065] Finally, the evaluation circuit also records the voltage drop across the compensating resistor 13. For this purpose, the equivalent circuit diagram according to Figure 4 the voltage measuring contacts U5 / U6 are shown.

[0066] Figure 5 shows a modification of the current measuring resistor 1 according to Figure 3 . The modification according to Figure 5 largely agrees with the current measuring resistor 1 according to Figure 3 so that, to avoid repetition, reference is made to the above description, the same reference numerals being used for corresponding details.

[0067] A special feature of this embodiment is that a notch 27, also referred to as a current shadow, is arranged in the power connection part 2 and surrounds the voltage measuring contact 17. The technical background and the functioning of such a current shadow are described, for example, in WO 2014 / 161624 A1. Thus, the current shadow enables an improvement in measurement accuracy.

[0068] Figure 6 shows a further modification of the current measuring resistor 1 according to Figure 5 , so that in order to avoid repetition, reference is again made to the above description, the same reference numerals being used for corresponding details.

[0069] A special feature of this embodiment is that an incision 28 is also arranged in the other power connection part 3.

[0070] Figure 7shows the temperature dependence of the current measurement of the main current I1 in various variations. The solid line shows the change without the compensating resistor RP or 13 and without taking into account the ohmic resistance R CU1 of the power connection parts 2, 3. The dashed line, on the other hand, shows the change taking into account the compensating resistor 13. Finally, the dotted line shows the change taking into account the compensating resistor RP and also taking into account the ohmic resistance R CU1 of the power connection parts 2, 3.

[0071] Figure 8 shows the temperature dependence of the current measurement of the secondary current I2 two in the secondary current path 26 for the same variants as in Figure 7 . List of reference symbols

[0072] 1Low-ohm current measuring resistor 2Current connection part of the current measuring resistor for introducing the current to be measured 3Current connection part of the current measuring resistor for dissipating the current to be measured 4Resistance element of the current measuring resistor 5, 6Holes in the current measuring resistor for attaching current contacts 7Printed circuit board 8Through-hole in the printed circuit board in front of the compensating resistor 9Through-hole in the printed circuit board behind the compensating resistor 10Printed circuit board track in front of the compensating resistor 11Printed circuit board track between the compensating resistor and the magnetic field sensor 12Printed circuit board track behind the magnetic field sensor 13Compensating resistor 14Hall sensor 15-20Voltage measuring contacts for measuring the voltage across the resistance element of the current measuring resistor 21-24Cuts in the current connection parts 25Main current path 26Sub-current path 27, 28 cuts (current shadow) Icurrent,to be measured I1Main current I2Side current R Shunt resistance of the resistance element of the current measuring resistor R Cu1 resistance of the current connection parts of the current measuring resistor RP resistance of the resistance element of the compensating resistor R CU2 resistance of the current connection parts of the compensating resistor R Cu0 resistance of the side current path before and after the compensating resistor U Hall Hall voltage U2 / U3Voltage measuring contacts for voltage measurement across the resistance element of the current measuring resistor U2a / U3aVoltage measuring contacts for voltage measurement across the resistance element of the current measuring resistor U5 / U6Voltage measuring contacts for voltage measurement across the resistance element of the compensating resistor,

Claims

1. Current measuring apparatus for measuring an electric current (I), comprising a) a low-resistance current measuring resistor (1) for current measurement according to the four-wire technique, and b) a magnetic field sensor (14), in particular as a Hall sensor or as a magnetoresistive magnetic field sensor, for redundant current measurement, c) wherein the electric current (I) to be measured is divided in the current measuring apparatus into a main current path (25) with a main current (I1) and a secondary current path (26) with a secondary current (I2), the main current path (25) and the secondary current path (26) together forming a parallel circuit, d) wherein the low-resistance current measuring resistor (1) is arranged in the main current path (25) and has the main current (I1) flowing through it, and e) wherein the magnetic field sensor (14) is arranged in the secondary current path (26) and measures the secondary current (I2), characterized in that f) the parallel circuit is designed such that the main current (I1) through the main current path (25) with the low-resistance current measuring resistor (1) is greater than the secondary current (I2) in the secondary current path (26) with the magnetic field sensor (14), namely by a factor of at least 10.

2. Current measuring apparatus according to claim 1, characterized in that the parallel circuit is designed such that the main current (I1) through the main current path (25) with the low-resistance current measuring resistor (1) is greater than the secondary current (I2) in the secondary current path (26) with the magnetic field sensor (14), namely by a factor of at least 100, 200, 500 or 1000.

3. Current measuring apparatus according to one of the preceding claims, characterized in a) that the secondary current path (26) has an electrical resistance value which is greater than the resistance of the main current path (25) by a factor of at least 10, 100, 200, 500 or 1000, and / or b) that the resistance value of the main current path (25) lies in the range of 1 µΩ, 10 µΩ, 20 µΩ, 50 µΩ, 100 µΩ, 200 µΩ or 500 µΩ with a deviation of at most ±50%, ±20%, ±10%, ±5%, ±2% or ±1%, and / or c) that the resistance value of the secondary current path lies in the range of 1 mΩ, 2 mΩ, 5 mΩ, 10 mΩ, 20 mΩ, 50 mΩ or 100 mΩ with a deviation of maximum ±50%, ±20%, ±10%, ±5%, ±2% or ±1%.

4. Current measuring apparatus according to one of the preceding claims, characterized in that the low-resistance current measuring resistor (1) has a larger current measuring range than the magnetic field sensor (14), in particular by a factor of at least 10, 100, 200, 500 or 1000.

5. Current measuring apparatus according to any one of the preceding claims, characterized in a) that a compensating resistor (13) is arranged in the secondary current path (26) with the magnetic field sensor (14), b) that the compensating resistor (13) is dimensioned with respect to its resistance value such that the temperature dependence of the resistance value of the conductor material is at least partially compensated for, c) that the main current path (25) and the secondary current path (26) each contain conductor material with a specific first temperature coefficient with respect to the resistance value and resistor material with a specific second temperature coefficient with respect to the resistance value, d) that the first temperature coefficient of the conductor material is preferably substantially greater than the second temperature coefficient of the resistor material, in particular by a factor of at least 10, 20, 50, 100 or 200, e) that the compensating resistor (13) in the secondary current path (26) consists of a resistor material which preferably has a substantially lower temperature coefficient than the conductor material.

6. Current measuring apparatus according to claim 5, characterized in that the main current path (25) and the secondary current path (26) have the same resistance ratio between the resistance value of the conductor material and the resistance value of the resistor material, in particular with a deviation of less than ±20%, ±10%, ±5%, ±2%.

7. Current measuring apparatus according to claim 5 or 6, characterized in a) that the first temperature coefficient of the conductor material is in the range of 1,000-10,000 or 3,600-4,000 ppm / K, and / or b) that the second temperature coefficient of the resistor material is in the range of 0 to ±100 ppm / K, 0 to ±50 ppm / K, 0 to ±20 ppm / K or 0 to ±10 ppm / K.

8. Current measuring apparatus according to one of the preceding claims, characterized in that the low-resistance current measuring resistor (1) is plate-shaped, with plate-shaped current connecting parts (2, 3) and a plate-shaped resistor element (4), the plate-shaped resistor element (4) being arranged between the two plate-shaped current connecting parts (2, 3) in the direction of current flow.

9. Current measuring apparatus according to claim 8, characterized in, a) that at least one of the two plate-shaped current connecting parts (2, 3) of the low-resistance current measuring resistor (1) has an incision (21-24) on one or both sides for temperature compensation, and / or b) that at least one of the two plate-shaped current connecting parts (2, 3) has an incision (27, 28) in the center for trimming the resistance value.

10. Current measuring apparatus according to any one of claims 8 to 9, characterized in a) that a plurality of voltage measuring contacts (15-20; U2, U2a, U3, U3a) are arranged on the plate-shaped current connecting parts (2, 3) of the low-resistance current measuring resistor (1), b) that the voltage measuring contacts (15-20; U2, U2a, U3, U3a) are distributed transversely to the current flow direction, and / or c) that the central incision (27) in the plate-shaped current connecting part (2) surrounds one of the voltage measuring contacts (15-20; U2, U2a, U3, U3a) as a current shadow.

11. Current measuring apparatus according to one of claims 8 to 10, characterized in a) that a printed circuit board (7) is arranged on the plate-shaped current measuring resistor (1), and / or b) that the printed circuit board (7) makes contact with the two current connecting parts (2, 3) of the low-resistance current measuring resistor (1) by means of in each case at least one through-plating (8, 9), and / or c) that the magnetic field sensor (14) is arranged on the printed circuit board (7), and / or d) that the magnetic field sensor (14) on the one hand and the current measuring resistor (1) on the other hand are arranged on opposite sides of the printed circuit board (7), and / or e) that the compensating resistor (13) is arranged on the printed circuit board (7), in particular on the same side as the magnetic field sensor (14), and / or f) that the secondary current path (26) runs on and / or in the printed circuit board (7), while the main current path (25) runs through the low-resistance current measuring resistor (1), and / or g) that an evaluation circuit is arranged on the printed circuit board (7), which detects the following: g1) the voltage drop across the resistance element (4) of the low-resistance current measuring resistor (1), g2) the output signal of the magnetic field sensor (14), and / or g3) the voltage drop across the compensating resistor (13) in the secondary current path (26), and / or h) that the evaluation circuit has an interface for outputting the output signal of the magnetic field sensor (14).

12. Current measuring apparatus according to claim 11, characterized in, a) that the printed circuit board (7) has several layers, b) that the compensating resistor (13) is arranged on the uppermost layer of the printed circuit board (7), c) that the secondary current path (26) upstream of the compensating resistor (13) is divided among a plurality of layers of the printed circuit board (7), d) that the secondary current path (26) is brought together upstream of the compensating resistor (13) on the uppermost layer of the printed circuit board (7) and then runs completely through the compensating resistor (13) on the uppermost layer of the printed circuit board (7), and e) that the secondary current path (26) downstream of the compensating resistor (13) is again divided into several layers of the printed circuit board (7).

13. Current measuring apparatus according to one of the preceding claims, characterized by voltage measuring contacts (U5, U6) for measuring the electrical voltage dropping across the compensating resistor (13) for a current measurement according to the four-wire technique also in the secondary current path (26), so that the current measurement in the secondary current path (26) is carried out both according to the four-wire technique and by the magnetic field sensor (14).

14. Current measuring apparatus according to any of the preceding claims, characterized in a) that the current measuring apparatus has a high-voltage area and a low-voltage area, b) that the magnetic field sensor (14) measures the secondary current (I2) on the input side in the high-voltage area, and c) that the magnetic field sensor (14) outputs the output signal on the output side in the low-voltage area, d) that the compensating resistor (13) is preferably arranged in the high-voltage area, e) that the magnetic field sensor (14) preferably contains an insulation which insulates the low-voltage area from the high-voltage area.

15. Current measuring apparatus according to any of the preceding claims, characterized in a) that the current measuring apparatus has a current measuring range that extends to at least 0.5 kA, 1 kA, 2 kA, 5 kA, 10 kA or 20 kA, and / or b) that the current measuring apparatus permits an operating voltage of at least 100 V, 500 V or 1 kV on the input side, and / or c) that the conductor material of the current connecting parts (2, 3) of the low-resistance current measuring resistor (1) is copper or a copper alloy or aluminum or an aluminum alloy, and / or d) that the resistance material of the resistance element (4) of the low-resistance current measuring resistor (1) is one of the following alloys: d1) a copper alloy, in particular a copper-manganese-nickel alloy, in particular CuMn12Ni2, Cu84Ni4Mn12 or Cu65Mn25Ni10, or a copper-manganese-tin alloy, in particular CuMn7Sn2,3, or a copper-chromium alloy, d2) a nickel alloy, in particular NiCr or CuNi, and / or e) that the conductor material of the current connecting parts (2, 3) of the low-resistance current measuring resistor (1) has a lower specific electrical resistance than the resistance material of the resistance element (4) of the low-resistance current measuring resistor (1), and / or f) that the resistive material of the resistor element (4) of the low-resistance current measuring resistor (1) has a specific electrical resistance of less than 1000 µΩcm, 500 µΩcm, 250 µΩcm, 100 µΩcm or 50 µΩcm, and / or g) that the conductor material of the current connecting parts (2, 3) of the low-resistance current measuring resistor (1) has a specific electrical resistance of less than 20 µΩcm, 10 µΩcm, 5 µΩcm or 2 µΩcm, and / or h) that the magnetoresistive magnetic field sensor (14) is a GMR sensor, and / or i) that the low-resistance current measuring resistor (1) has a resistance value which is at most 500 mΩ, 200 mΩ, 100 mΩ, 50 mΩ, 20 mΩ, 10 mΩ, 5 mΩ, 2 mΩ or 1 mΩ.