Current measuring device and associated operating procedure

Abstract

The invention relates to a current measuring device for measuring an electric current (I), comprising a current-sensing resistor (2), wherein the current (I) to be measured flows through the current-sensing resistor (2) and the current-sensing resistor (2) exhibits an aging-related drift in its resistance value (R), which depends on the temperature-time profile (TP) of the current-sensing resistor (2) during the operating time (t). Furthermore, the current measuring device according to the invention comprises a voltage measuring device (3) for measuring the voltage drop (U) across the current-sensing resistor (2), and an evaluation unit (6) which is connected to the voltage measuring device (3) at its input and calculates the electric current (I) flowing through the current-sensing resistor (2) as a function of the measured voltage (U) and the resistance value (R) of the current-sensing resistor (2) according to Ohm's law.The invention is characterized in that the evaluation unit (6) at least partially compensates for the age-related drift of the resistance value (R) of the current measuring resistor (2) when calculating the current (I) according to Ohm's law. Furthermore, the invention includes a corresponding operating method for such a current measuring device.

Description

Technical field of the invention

[0001] The invention relates to a current measuring device for measuring an electric current using the four-wire technique. Furthermore, the invention relates to an operating method for such a current measuring device. Background of the invention

[0002] To measure an electric current, it is known from the prior art (e.g., EP 0 605 800 A1) to use a low-ohm current measuring resistor, with the current measurement being performed using the four-wire technique. The electric current to be measured is passed through the low-ohm current measuring resistor, and the voltage across the current measuring resistor is measured. From the voltage drop across the current measuring resistor and the known resistance value of the current measuring resistor, the electric current flowing through the current measuring resistor can then be calculated according to Ohm's law.

[0003] The problem with this well-known type of current measurement is the fact that measurement errors occur when the current measuring resistor is operated over longer periods of time.

[0004] For the general technical background of the invention, reference should also be made to US 2011 / 0 298 473 A1.

[0005] Finally, KR 10 2019 0 075 812 A discloses a current measuring device and an associated operating method according to the preamble of the independent claims. However, this prior art is not yet entirely satisfactory. Description of the invention

[0006] The invention is therefore based on the object of creating a correspondingly improved current measuring device which does not show such incorrect measurements even during longer operating periods.

[0007] This object is achieved by a current measuring device according to the invention or by an associated operating method according to the independent claims.

[0008] The invention is based on the discovery that incorrect measurements of the electrical current that occur during extended periods of operation are due to the resistance of the current measuring resistor exhibiting an aging-related drift. This means that the resistance of the current measuring resistor is not constant over time, but changes gradually over the operating period. Failure to take this gradual, aging-related change in the resistance of the current measuring resistor into account leads to a measurement error when calculating the electrical current from the voltage drop across the current measuring resistor and the resistance of the current measuring resistor.

[0009] The invention therefore provides that the age-related drift of the resistance value of the current measuring resistor is at least partially compensated in order to avoid age-related measurement errors.

[0010] The current measuring device according to the invention, in accordance with the known current measuring device described at the outset, firstly has a low-ohmic current measuring resistor, wherein the electrical current to be measured is passed through the current measuring resistor, as is also the case with conventional current measurement according to the four-wire technique.

[0011] In addition, the current measuring device according to the invention, in accordance with the known current measuring device described at the outset, also has a voltage measuring device in order to measure the electrical voltage dropping across the current measuring resistor.

[0012] Furthermore, the current measuring device according to the invention, in accordance with the known current measuring device described at the outset, also has an evaluation unit which is connected on the input side to the voltage measuring device and calculates the electrical current flowing through the current measuring resistor as a function of the measured voltage and the predetermined resistance value of the current measuring resistor in accordance with Ohm's law.

[0013] The invention now additionally provides that the evaluation unit at least partially compensates for the age-related drift of the resistance value of the current measuring resistor when calculating the current according to Ohm's law.

[0014] When compensating for the age-related drift of the resistance value of the current measuring resistor, it can be assumed that this drift is significantly influenced by the temperature-time profile of the current measuring resistor during its operating life. If, for example, the current measuring device according to the invention is not used for an extended period of time, the temperature-time profile will not exhibit any temperature peaks during this time, which will then cause, at most, a slight age-related drift of the resistance value of the current measuring resistor. If, on the other hand, the current measuring device is continuously used to measure high electrical currents, the temperature-time profile of the current measuring resistor will exhibit strong temperature peaks, which will lead to a correspondingly strong age-related drift of the resistance value of the current measuring resistor.The current measuring device according to the invention therefore preferably has a timer to measure the elapsed operating time of the current measuring resistor, since the elapsed operating time of the current measuring resistor is a significant influencing factor for the age-related drift of the resistance value.

[0015] According to the invention, the actual temperature of the current measuring resistor is measured by means of a temperature measuring device.

[0016] The current measuring device has a timer to measure the elapsed operating time of the current measuring resistor, since the elapsed operating time of the current measuring resistor, along with the temperature-time profile, is a significant influencing factor for the aging-related drift of the resistance value of the current measuring resistor. According to the invention, the evaluation unit is connected to both the temperature measuring device and the timer and then continuously determines the actual temperature-time profile of the current measuring resistor during the operating time of the current measuring resistor. The temperature-time profile of the current measuring resistor is therefore not simply estimated but actually measured, which enables more precise compensation for the aging-related drift of the resistance value.The evaluation unit can then compensate for the aging-related drift in the resistance value of the current measuring resistor based on the measured temperature-time profile and the elapsed operating time. To do this, the evaluation unit calculates a corrected resistance value from the measured temperature-time profile and the elapsed operating time, which also takes into account the aging-related drift in the resistance value of the current measuring resistor. This correction of the resistance value can be performed using aging models determined by the manufacturer based on practical measurements. For example, current measuring resistors can be subjected to aging tests at the current measuring resistor manufacturer, in which the current measuring resistors are exposed to specific temperature-time profiles, during which the aging-related drift in the resistance value of the current measuring resistor is measured.In this way, an aging model can be stored in the evaluation unit, whereby the aging model can take into account the resistance material, the connection to the resistance material, the positioning of the current measuring resistor and the respective temperature-time profile.

[0017] The aging drift of the current measuring resistor of the current measuring device over its service life can be determined using environmental simulation tests of the current measuring resistors. The environmental simulation tests (e.g., high-temperature exposure or temperature cycling tests) are based on accelerated temperature and / or load profiles calculated using the Arrhenius model or the Coffin-Manson model. The determined aging drift-service life curves are stored in the current measuring device to correct the aging drift of the current measuring resistor and used for the correction calculation.

[0018] The above only addressed the measurement errors caused by the aging-related drift of the resistance value of the current measuring resistor. In addition, the resistance value of the current measuring resistor also exhibits a temperature-dependent drift corresponding to the current temperature of the current measuring resistor. While care is taken when selecting the resistance material of the current measuring resistor to ensure that the resistance value of the current measuring resistor exhibits as little temperature dependence as possible, this disruptive temperature dependence cannot be completely prevented. Therefore, in a preferred embodiment of the invention, it is provided that the evaluation unit also compensates for the temperature-dependent drift of the resistance value of the current measuring resistor according to the currently measured temperature when calculating the current according to Ohm's law.The evaluation unit is able to do this because it measures the current temperature of the current measuring resistor via the temperature measuring device and knows the temperature coefficient or, in general, the temperature dependence of the resistance value of the current measuring resistor.

[0019] Within the scope of the invention, it is also possible to specify a current load profile that reflects the temporal progression of the current flowing through the current measuring resistor during the previous operating period. Such a current load profile is easier to specify than the temperature-time profile, depending on the specific application. Nevertheless, specifying the current load profile is also suitable for determining and compensating for the aging-related drift of the resistance value of the current measuring resistor, because the temperature of the current measuring resistor depends significantly on the current flowing through the current measuring resistor. The evaluation unit can then compensate for the aging-related drift of the resistance value based on the elapsed operating period and the specified current load profile. The current load profile is actually measured in this case.

[0020] In general, it should be noted that the current measuring resistor is preferably low-ohmic, in particular with a resistance value of at most 100 mΩ, 25 mΩ, 10 mΩ, 5 mΩ, 2 mΩ, 1 mΩ, 500 μΩ or 250 μΩ.

[0021] In the preferred embodiment of the invention, the current measuring resistor is connected to two connecting parts made of a conductor material, wherein the connecting parts and the current measuring resistor are preferably plate-shaped, as is also known from the prior art cited at the outset (cf. EP 0 605 800 A1).

[0022] The connection parts of the current measuring resistor are preferably made of a conductor material such as copper, a copper alloy, aluminum or an aluminum alloy.

[0023] The current measuring resistor, on the other hand, is preferably made of a resistance material that has a lower specific electrical conductivity than the conductor material of the connecting parts.

[0024] For example, the resistance material of the current measuring resistor can be one of the following alloys: • a copper alloy, in particular a copper-manganese-tin alloy, in particular CuMn12Ni2 or CuMn7Sn2.3, or a copper-manganese-nickel alloy, in particular Cu84Ni4Mn12 or Cu65Mn25Ni10, or a copper-chromium alloy, • a nickel alloy, in particular NiCr or CuNi.

[0025] Furthermore, it should be mentioned in general that the current measuring resistor is preferably electrically and mechanically connected to the two connecting parts, in particular by a welded connection (e.g. electron beam welding).

[0026] Regarding electrical conductivity, it should be noted that the resistance material of the current measuring resistor preferably has a specific electrical resistance that is less than 2·10 4 Ω-m, 2·10 -5 Ω·m or 2·10 6Ω·m, and / or greater than 2·10 6 Ω·m, 2·10 7 Ω·m, while the conductor material of the connecting parts has a specific electrical resistance of less than 10 -6 Ω·m or 10 -7 Ω·m.

[0027] Above, the current measuring device according to the invention has been described independently of the respective application. However, the invention also claims protection for a system (e.g., the on-board electrical system of a motor vehicle) with such a current measuring device and an electrical network (e.g., the on-board electrical system of the motor vehicle), wherein the electrical current measured by the current measuring device flows in the network. However, the invention is not limited to current measurement in the on-board electrical system of a motor vehicle, but can also be used in stationary systems.

[0028] Furthermore, it should be mentioned that the current measuring device preferably has a control unit which optionally sets an active mode of the current measuring device or a passive mode (sleep mode) of the system.

[0029] In the active mode of the system, the electrical network is switched on and the current measuring resistor measures the electrical currents flowing during operation, whereby the temperature-time profile of the current measuring resistor can then also be measured.

[0030] In passive mode, however, the electrical network is switched off, so that the current measuring resistor is generally not energized. However, in passive mode, it is preferably provided that the current measuring device regularly "wakes up" and then performs a temperature measurement in order to be able to determine the temperature-time profile of the current measuring resistor even in passive mode. The temperature and / or voltage measurements in passive mode preferably occur at a significantly longer time interval than in active mode, i.e., the voltage and / or temperature measurements occur much less frequently in passive mode than in active mode.The evaluation unit can then determine the temperature-time profile of the current measuring resistor based on the measured temperature values ​​in the active mode and / or in the passive mode in order to determine the age-related drift of the resistance value of the current measuring resistor on the basis of the temperature-time profile thus determined.

[0031] In addition to the current measuring device according to the invention described above and a system with such a current measuring device according to the invention, the invention also claims protection for a corresponding operating method, wherein the individual method steps of the operating method according to the invention already result from the above description, so that a separate description of the individual method steps can be dispensed with.

[0032] 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. Brief description of the drawings Fig. 1 shows a schematic representation of a current measuring device according to the invention with a compensation of the age- and temperature-related drift of the resistance value of the current measuring resistor. Fig. 2 shows a flow chart to illustrate the operating method according to the invention. Fig. 3 shows a non-inventive modification of Fig. 2. Fig. 4 shows a flow chart to illustrate the operation of the current measuring device according to the invention in active mode and in passive mode. Detailed description of the drawings

[0033] Fig. Figure 1 shows a schematic representation of a current measuring device according to the invention for measuring an electrical current I according to the known four-wire technique. The electrical current I to be measured is conducted via a power line 1 through a low-ohm current measuring resistor 2. A voltage measuring device 3 measures the electrical voltage U across the current measuring resistor 2 via two voltage taps 4, 5.

[0034] Furthermore, the current measuring device according to the invention, in accordance with the prior art, comprises an evaluation unit 6 which calculates the electrical current I flowing through the current measuring resistor 2 from the electrical voltage U dropped across the current measuring resistor 2 and the known resistance value R of the current measuring resistor 2 in accordance with Ohm's law. The evaluation unit 6 comprises a module 7 for this current calculation.

[0035] It has already been explained above that the resistance value R of the current measuring resistor 2 is not constant over time during operation, but rather exhibits an age-related drift that depends on the elapsed operating time t and the previous temperature-time profile TP to which the current measuring resistor 2 was exposed during the elapsed operating time t. To compensate for this age-related drift of the resistance value R of the current measuring resistor 2, the current measuring device according to the invention therefore initially has a timer 8 that measures the operating time t of the current measuring resistor 2.

[0036] In addition, the current measuring device according to the invention has a temperature measuring device 9 which measures the current temperature T of the current measuring resistor 2 by means of a temperature sensor 10.

[0037] The evaluation unit 6 now has a further module 11, which is connected on the input side to the timer 8 and to the temperature measuring device 9 and which continuously determines the temperature-time profile TP to which the current measuring resistor 2 is exposed during the operating time t and which significantly influences the age-related drift of the resistance value R of the current measuring resistor 2.

[0038] To compensate for this age-related drift, the evaluation unit 6 has a further module 12, which receives the measured temperature-time profile TP from the module 11 on the input side and also receives a resistance value R0 as a specification, which represents the resistance value of the current measuring resistor 2 without compensation for age- and temperature-related drift, for example at room temperature at the time of delivery.

[0039] Module 12 then calculates an age-compensated resistance value R(TP) based on a stored ageing model, which takes into account the age-related drift of the resistance value R.

[0040] In addition, the current measuring device according to the invention also enables temperature compensation of the resistance value R of the current measuring resistor 2. For this purpose, the current measuring device has a further module 13 which receives the age-compensated resistance value R(TP) from the module 12 and additionally carries out temperature compensation and outputs a resistance value R(T, TP) to the module 7 on the output side, which compensates both the age-related drift and the temperature-related drift of the resistance value R of the current measuring resistor 2, thereby minimizing measurement errors.

[0041] The following is the flow chart according to Fig. 2, which describes the operation of the current measuring device according to Fig. 1 illustrates this.

[0042] In a first step S1, the resistance value R0 of the current measuring resistor 2 is specified without taking aging effects into account and at a defined ambient temperature (e.g. room temperature).

[0043] In a next step S2, the elapsed operating time t of the current measuring resistor 2 is continuously measured using the timer 8 during operation of the current measuring resistor 2.

[0044] In the next step S3, the temperature-time profile TP of the current measuring resistor 2 is continuously measured during the operating time t.

[0045] In a subsequent step S4, the resistance value R(TP) changed due to aging is then calculated according to the actually measured temperature-time profile TP.

[0046] In the next step S5, a temperature-dependent compensation of the resistance value R(T, TP) is carried out according to the currently measured temperature T of the current measuring resistor 2.

[0047] In the next step S6, the voltage across the current measuring resistor 2 is measured, as is known from the prior art.

[0048] In the last step S7, the current I is calculated from the measured voltage U and the resistance value R(T, TP) adjusted for aging and temperature according to Ohm's law.

[0049] Fig. 3 shows a non-inventive modification of the flow chart according to Fig. 2, so that to avoid repetition, reference is made to the above description.

[0050] A special feature of this exemplary embodiment is that the temperature-time profile, which is an influencing variable for the aging-related drift of the resistance value of the current-sense resistor 2, is not measured. Instead, an estimated current load profile SLP is specified for the service life of the current-sense resistor 2, with the current load profile SLP being specified depending on the respective application. The current load profile SLP then also indirectly influences the aging-related drift of the resistance value R of the current-sense resistor 2, since the current supply to the current-sense resistor 2 significantly influences the temperature T of the current-sense resistor 2.

[0051] The following is the schematic flow diagram according to Fig. 4, which explains the active and passive mode of the current measuring device.

[0052] In a first step S1, it is first checked whether normal operation is present, after which the system then proceeds to step S2 if necessary.

[0053] In step S2, it is then checked whether the system (e.g. on-board power system of a motor vehicle) is in operation and is therefore in an active mode.

[0054] In the active mode according to step S3, the voltage across the current measuring resistor 2 and also the temperature T of the current measuring resistor 2 are then regularly measured. This measurement is clocked with a time interval t1.

[0055] In the next step S4, the temperature-time profile TP is measured during the operating period.

[0056] In the next step S5, the current I is calculated taking into account the measured temperature-time profile TP, with compensation for ageing and temperature.

[0057] In a subsequent step S6, the compensated current I is then output.

[0058] If, on the other hand, it is determined in step S2 that the system (e.g. the on-board power supply system of a motor vehicle) is switched off, the current measuring device is operated in a passive mode (sleep mode) according to step S7. In this sleep mode, the current measuring resistor 2 is not actually supplied with current, so that no measurements of temperature T and / or voltage U are taken. However, in this sleep mode, the current measuring device regularly “wakes up” in order to measure the voltage U and the temperature T at the current measuring resistor 2. This measurement is also clocked with a time interval t2, whereby this time interval t2 is considerably longer than the time interval t1 for the measurement in the active mode. In the passive mode (sleep mode), the measurement is therefore carried out considerably less frequently than in the active mode.

[0059] From step S1, it is optionally possible to proceed to a further step S8, in which the voltage U and the current T are measured regularly.

[0060] In step S9 it is then checked whether a correction of the lifetime dependency is necessary.

[0061] If this is the case, external correction parameters for the lifetime dependence of the current sensor can be received in step D10. For example, the aging model stored in the evaluation unit can be updated. Advantages of the invention

[0062] The invention enables compensation of the age-related drift of the resistance value of the current measuring resistor and thus minimization of measurement errors.

[0063] In addition, the invention also enables compensation of the temperature-related drift of the resistance value of the current measuring resistor, which also enables minimization of measurement errors.

[0064] The compensation of the age-related drift can be carried out according to an ageing model that has been empirically determined and can be stored in the evaluation unit.

[0065] In the preferred embodiment of the invention, both the age-related drift of the resistance value and the temperature-related drift of the current measuring resistor are compensated, whereby the measurement errors are then minimized. List of reference symbols 1 Current line through the current measuring resistor 2 current measuring resistor 3 Voltage measuring device for measuring the voltage across the current measuring resistor 4, 5 voltage taps on the current measuring resistor 6 Evaluation unit 7 Module of the evaluation unit for calculating the current according to Ohm's law 8 timer for measuring the operating time of the current measuring resistor 9 Temperature measuring device for measuring the temperature of the current measuring resistor 10 temperature sensors 11 Module of the evaluation unit for calculating the temperature-time profile of the current measuring resistor over the operating time 12 Module of the evaluation unit for ageing compensation 13 Module of the evaluation unit for temperature compensation Temperature sensor on the current measuring resistor I Current R0 Resistance value of the current measuring resistor without compensation for age and temperature-related drift R(TP) Resistance value of the current measuring resistor after ageing compensation R(T, TP) Resistance value of the current measuring resistor after ageing and temperature-related compensation t Operating time of the current measuring resistor T Temperature of the current measuring resistor TP Temperature-time profile of the current measuring resistor over the operating time U Voltage across the current measuring resistor

Claims

[1] Current measuring device for measuring an electric current (I), with a) a current measuring resistor (2), wherein a1) the current to be measured (I) flows through the current measuring resistor (2) and a2) the current measuring resistor (2) exhibits an age-related drift with respect to its resistance value (R), which drift depends on the temperature-time profile (TP) of the current measuring resistor (2) during the operating period (t), b) a voltage measuring device (3) for measuring the electrical voltage (U) dropping across the current measuring resistor (2), and c) an evaluation unit (6) which is connected on the input side to the voltage measuring device (3) and calculates the electrical current (I) flowing through the current measuring resistor (2) as a function of the measured voltage (U) and the resistance value (R) of the current measuring resistor (2) according to Ohm's law, d) wherein the evaluation unit (6) at least partially compensates for the age-related drift of the resistance value (R) of the current measuring resistor (2) when calculating the current (I) according to Ohm's law, characterized by , e) that the current measuring device has a temperature measuring device (9) which measures the current temperature (T) of the current measuring resistor (2), f) that the current measuring device has a timer (8) to measure the elapsed operating time (t) of the current measuring resistor (2), g) that the evaluation unit (6) is connected to the temperature measuring device (9) and the timer (8) and determines the temperature-time profile (TP) of the current measuring resistor (2) during the operating time (t), and h) that the evaluation unit (6) compensates for the age-related drift of the resistance value (R) of the current measuring resistor (2) on the basis of the measured temperature-time profile (TP) during the previous operating period. [2] Current measuring device according to claim 1, characterized by , that a) that the current measuring resistor (2) has a temperature-dependent drift with respect to its resistance value (R) corresponding to the current temperature (T) of the current measuring resistor (2), b) that the evaluation unit (6) compensates for the temperature-dependent drift of the resistance value (R) of the current measuring resistor (2) in accordance with the currently measured temperature (T) when calculating the current (I) according to Ohm's law. [3] Current measuring device according to one of the preceding claims, characterized by , a) that the evaluation unit (6) determines an actual current load profile during operation, wherein the current load profile reflects the temporal course of the current (I) flowing through the current measuring resistor (2) during the previous operating time, and b) that the evaluation unit (6) compensates for the age-related drift of the resistance value (R) of the current measuring resistor (2) on the basis of the elapsed operating time (t) and the measured current load profile (SLP) during the previous operating time of the current measuring resistor (2). [4] Current measuring device according to one of the preceding claims, characterized by , a) that the current measuring resistor (2) is low-ohmic, in particular with a resistance value (R) of at most 100 mΩ, 25 mΩ, 10 mΩ, 5 mΩ, 2 mΩ, 1 mΩ, 500 μΩ or 250 μΩ, and / or b) that the current measuring resistor (2) is connected to two connecting parts made of a conductor material, and / or c) that the conductor material of the connecting parts is copper, a copper alloy, aluminium or an aluminium alloy, and / or d) that the current measuring resistor (2) consists of a resistance material which has a lower specific electrical conductivity than the conductor material of the connecting parts, and / or e) that the resistance material of the current measuring resistor (2) is one of the following alloys: e1) a copper alloy, in particular a copper-manganese-tin alloy, in particular CuMn12Ni2 or CuMn7Sn2.3, or a copper-manganese-nickel alloy, in particular Cu84Ni4Mn12 or Cu65Mn25Ni10, or a copper-chromium alloy, e2) a nickel alloy, in particular NiCr or CuNi, and / or f) that the current measuring resistor (2) is electrically and mechanically connected to the two connecting parts, in particular by a welded connection, in particular by electron beam welding, and / or g) that the current measuring resistor (2) and / or the connecting parts are plate-shaped, and / or h) that the resistance material has a specific electrical resistance of less than 2·10 -4 Ω-m, 2·10 -5 Ω·m or 2·10 -6 Ω·m, and / or i) that the resistance material has a specific electrical resistance greater than 2·10 -6 Ω·m, 2·10 -7 Ω·m, and / or j) that the conductor material of the connecting parts has a specific electrical resistance of less than 10 -6 Ω·m or 10 -7 Ω·m. [5] System, in particular the on-board power system of a motor vehicle, with a) a current measuring device according to one of the preceding claims, and b) an electrical network, in particular an on-board network of the motor vehicle, wherein the electrical current (I) measured by the current measuring device flows in the network. [6] Plant according to claim 5, characterized by , (a) that the current measuring device has a control unit which optionally sets an active mode of the system or a passive mode of the system, b) that in the active mode the electrical network is switched on and energises the current measuring resistor (2), and c) that in the passive mode the electrical network is switched off and does not supply current to the current measuring resistor (2). [7] Plant according to claim 6, characterized by , a) that the current measuring device in the active mode regularly measures the following quantities at a first time interval, a1) the voltage (U) across the current measuring resistor (2), and / or a2) the temperature (T) of the current measuring resistor (2), b) that the current measuring device in the passive mode regularly measures the following quantities at a second time interval: b1) the voltage (U) across the current measuring resistor (2), and / or b2) the temperature (T) of the current measuring resistor (2), and c) that a separate voltage source is preferably provided for the power supply of the current measuring device and / or the evaluation unit (6) in the passive mode, d) that the second time interval is preferably substantially longer than the first time interval, in particular at least by a factor of 10, 100, 1000 or 10000, e) that the evaluation unit (6) determines the temperature-time profile (TP) of the current measuring resistor (2) preferably on the basis of the measured values ​​of the temperature (T) in the active mode and / or in the passive mode. [8] Operating method for a current measuring device according to one of claims 1 to 4 or a system according to one of claims 5 to 7, comprising the following steps: a) Passing the current to be measured (I) through the current measuring resistor (2), b) measuring the voltage (U) across the current measuring resistor (2) while the current (I) to be measured flows through the current measuring resistor (2), and c) Calculating the current (I) flowing through the current measuring resistor (2) according to Ohm's law from the measured voltage (U) across the current measuring resistor (2) and the resistance value (R) of the current measuring resistor (2), d) compensating for the age-related drift of the resistance value (R) of the current measuring resistor (2) when calculating the current (I) flowing through the current measuring resistor (2), characterized by The following steps are used to compensate for the age-related drift of the resistance value (R) of the current measuring resistor (2) when calculating the current (I) flowing through the current measuring resistor (2): e) measuring the elapsed operating time (t) of the current measuring resistor (2), f) measuring the temperature (T) of the current measuring resistor (2) over the operating time (t), g) calculating the actual temperature-time profile (TP) of the current measuring resistor (2) over the operating time (t) based on the measured operating time (t) and the measured temperature (T) of the current measuring resistor (2), and h) Compensating for the age-related drift of the resistance value (R) of the current measuring resistor (2) as a function of the elapsed operating time (t) of the current measuring resistor (2) and the measured temperature-time profile (TP) of the current measuring resistor (2) during the elapsed operating time of the current measuring resistor (2). [9] Operating method according to claim 8, characterized by , a) that the current measuring resistor (2) has a temperature-dependent drift with respect to its resistance value (R) corresponding to the current temperature (T) of the current measuring resistor (2), b) that the current temperature (T) of the current measuring resistor (2) is measured, and c) that the temperature-dependent drift of the resistance value (R) of the current measuring resistor (2) is compensated according to the currently measured temperature (T).

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