Diagnostic method and measurement arrangement for a component to be examined

Abstract

The invention relates to a method and to a measurement arrangement for diagnosing a component to be examined, said method comprising the steps of: operating the component (10) to be examined in an electrical circuit (11) at a predefined operating point for a predefined first measurement interval (12); and, during this first measurement interval, detecting a measurement signal and an excitation signal (13) in the circuit as a function of time, wherein the excitation signal is a signal from a passive component (14) in the circuit, which signal is in a predefined first excitation state (15) at the start of the first measurement interval, and the measurement signal results from a superposition of the excitation signal of the passive component and an operating signal from the component to be examined.

Description

[0001] Description

[0002] Diagnostic procedure and measuring arrangement for a component to be examined

[0003] The invention relates to the diagnostics of electrochemical elements, such as galvanic primary or secondary cells, batteries, electrolysis or fuel cells or stacks.

[0004] For a deeper analysis of the state of electrochemical elements (e.g. in Li-ion batteries as well as in fuel cells and electrolysis cells), the method of impedance spectroscopy is known.

[0005] In this method, the cell (Li-ion cell or fuel cell, etc.) is periodically stimulated externally during operation. This excitation can be a cyclic increase and decrease of the output current (e.g., via a frequency-modulated load) or an excitation voltage superimposed on the operating voltage. Typically, a frequency generator is used for this purpose, generating a fully symmetrical signal (e.g., a sine wave), which is transmitted to the cell via a voltage source (called "potentiostatic") or an electrical load (called "galvanostatic"). The resulting response signal (voltage fluctuation in the case of galvanostatic excitation, or current signal fluctuation in the case of potentiostatic excitation) is measured on the cell under test. A Fourier analysis of the resulting phase shift from the excitation to the response signal at different excitation frequencies provides information about the real and imaginary parts of the cell's intrinsic impedance.Basic functions and processes can be found in numerous books and publications.

[0006] Technically, this method is complex and susceptible to interference for several reasons: The generation of the periodic excitation signals typically requires a frequency generator capable of generating a wide spectrum of different frequencies. Typically, many frequencies are scanned per measurement in order to map a complex, frequency-dependent impedance pattern. Furthermore, the signals must be transmitted cleanly and with signal fidelity to the cell using suitable voltage sources / current sinks, etc. Interference from cables and lines or the measurement setup regarding inductances and capacitances must be laboriously circumvented or measured out using calibration in order to derive a "clean" diagnosis of the measuring cell under investigation from the analysis. Ideally, one setup should be identical for all (repeated) measurements (e.g., aging measurements over time or, after damage to the measuring cell, possibly due to temperature influences, etc.), i.e.be repeatable in terms of location and / or structure. Likewise, external disturbances on the signal path to be examined / excited must be avoided (e.g., load steps during a measurement cycle). The signals to be examined must be resolved very precisely (both the signal strength and the temporal correlation to the excitation). The procedure - especially for a broad frequency spectrum (depending on the observed characteristics of the cell under investigation) - requires a certain measurement time. This is difficult to implement, especially in mobile applications (e.g., for online analysis in the vehicle). The described restrictions regarding the required hardware severely limit implementation in mobile applications or applications that cannot be operated at a fixed time. In addition, the required devices and configuration variants are comparatively cost-intensive.

[0007] The invention is therefore based on the object of providing a method and a device for cell diagnostics which avoids the above-mentioned difficulties.

[0008] This object is achieved by a method and a device according to the independent claims. Advantageous further developments are specified in the dependent claims.

[0009] The diagnostic method according to the invention is suitable, for example, for the impedance analysis of batteries, fuel or electrolysis cells, or other electrochemical elements. These are referred to as components to be examined within the scope of this invention. In particular, the methods and devices according to the invention can be advantageously used for the diagnosis of fuel cells (stacks) in vehicles. To carry out the method according to the invention, a component to be examined is operated in an electrical circuit for a predetermined first measurement interval at a predetermined operating point. A predetermined operating point here means, in particular, a defined, reproducible, and / or preferably constant operating point in order to advantageously enable reproducibility and comparability of the diagnostic method according to the invention.

[0010] During the first measurement interval, a passive component is connected to the circuit. At the beginning of the first measurement interval, the passive component is in a predetermined first excitation state. For the duration of the measurement interval, a measurement signal and an excitation signal from the passive component are detected in the circuit as a function of time. The measurement signal results from a superposition of the excitation signal from the passive component and an operating signal from the component under test.

[0011] The measurement signal and the excitation signal can then preferably be evaluated and conclusions can be drawn about the condition of the component to be examined.

[0012] The passive component is, for example, a capacitor, a coil (inductor), or a resistor. The predefined excitation state can then be, for example, a charge with a specific voltage in the case of a capacitor, a specific temperature of a (temperature-dependent) resistor, or a specific magnetization state of the coil. However, the predefined excitation state can also be a ground state, e.g., 0 voltage in the case of a capacitor, or no magnetization in the case of a coil.

[0013] While the passive component is connected to the circuit, it transmits an excitation signal into the circuit during the first measurement interval. The excitation signal of a capacitor is, for example, a charging or discharging current. This charging (discharging) current follows a characteristic temporal characteristic depending on the capacitor's design. Different capacitors can differ, for example, in their capacitance and dielectric strength, as well as their charging and discharging characteristics and their time constant (T). Typical capacitances, for example, are in the range from 200 pF to 2 mF.

[0014] Accordingly, resistors can differ in terms of their temperature dependence, and inductances, for example, in terms of their magnetic permeability, number of windings, etc. These properties of the passive components, in addition to the excitation state, are decisive for the course of the excitation signal in the circuit and are referred to in this application as the characteristic of the respective passive component.

[0015] The specified measurement interval is a time interval during which a measurement is taken. The specified measurement interval can preferably be selected depending on the characteristics of the respective passive component. For example, an advantageous measurement interval for a capacitor is three to four times the capacitor's time constant. The duration of a measurement interval is, for example, between 0.5 ms and 5 s. A duration between 100 ms and 1 s, e.g., 150 ms, is advantageous.

[0016] According to a preferred development of the method according to the invention, after the first measuring interval has elapsed, at least one further passive component is switched on for a predetermined further measuring interval. At the beginning of the further measuring interval, this further passive component is in a predetermined second excitation state. For the duration of the further measuring interval, the measuring signal and the excitation signal in the circuit are again detected as a function of time. In this case, the excitation signal is generated by the at least one additional passive component, and the measuring signal results from the superposition of the excitation signal with the operating signal of the component to be tested. Preferably, the first passive component is disconnected from the circuit, for example by opening a switch, before the further measuring interval. The first passive component can then advantageously be returned to the predetermined first excitation state.In the case of a capacitor, this can be done, for example, by connecting it to a voltage source and charging the capacitor accordingly.

[0017] In the described variant, it is particularly advantageous if the first passive component and the at least one further passive component differ in their characteristics and / or at least each assume different predefined excitation states. This allows different excitation signals to be generated successively in the circuit, which then superimpose the operating signal of the component under test and thus produce different measurement signals. This allows additional information about the condition of the component under test to be obtained.

[0018] It is also possible to connect several additional passive components sequentially into the circuit, each for a specified measurement interval. It is particularly advantageous to connect a total of 3, 4, or 5 different passive components, each with different characteristics (reference value, time constants, etc.), one after the other into the circuit and detect the respective measurement signal. Combinations of similar passive components are possible, for example, two or more capacitors with different characteristics, as well as combinations of different passive components with each other, i.e., combinations of capacitor(s), coils, and / or resistors.

[0019] In one embodiment of the method according to the invention with several different passive components, measurement intervals of different lengths can be combined sequentially. The length of the measurement intervals is preferably adapted to the characteristics of the respective passive components. This means that when different passive components are switched on alternately or sequentially, measurement intervals of different lengths can follow one another. According to an alternative variant of the method according to the invention, it is also possible to successively bring one and the same passive component into different excitation states and to perform several consecutive measurements starting from different excitation states.Accordingly, after the first (and / or a subsequent) measurement interval has elapsed, the first passive component is brought into a further predefined excitation state that differs from the first excitation state, and the measurement of the excitation signal and the measurement signal is repeated in a subsequent measurement interval, with the first passive component being in the further excitation state that differs from the first excitation state at the beginning of the subsequent measurement interval. This variant advantageously allows different excitation signals and measurement signals to be generated, thereby avoiding additional costs for additional passive components.

[0020] Of course, the described variants can also be combined with each other. Different passive components can be combined, each of which can also assume different excitation states.

[0021] The method according to the invention allows time-dependent excitation signals to be generated in the circuit using one or more passive components and superimposed on the operating signal of the component under test. By evaluating a temporal correlation between the excitation signal and the measurement signal, the impedance behavior of the component under test can then be advantageously deduced.

[0022] The measurements described above can be performed repeatedly, particularly advantageously. For this purpose, the respective predefined excitation state for the passive component(s) is restored after their respective predefined measurement intervals have elapsed, before a new measurement can be performed. In the case of a capacitor, this is done, for example, by charging with a predefined voltage; a resistor, for example, is heated to a predetermined temperature.

[0023] According to a particularly advantageous development of the method, the measurements are performed periodically at a specific repetition frequency. In the simplest case, a first passive component is periodically brought into its excitation state, connected to the circuit for the duration of a measurement interval to generate an excitation signal, and returned to the excitation state after the measurement interval before it can again emit an excitation signal in the circuit, and so on. Typical repetition frequencies can, for example, be in the range between 1 Hz and 10 kHz, advantageously in the range of 1 kHz to 3 kHz.

[0024] Through the periodic execution, a periodic excitation signal is generated in the circuit. Preferably, the time-dependent measurement of the excitation signal and the measurement signal is then not limited to the individual measurement intervals (during which the passive component is connected to the circuit), but is continued continuously over at least several periods. The measured excitation signal and measurement signal thus obtained are thus also periodic with the repetition frequency. The excitation signal of a capacitor then corresponds, for example, to periodic current pulses that exhibit the characteristic curve for the respective capacitor.

[0025] It is advantageous if a period consists not only of a single excitation pulse, i.e., a single excitation signal from a single passive component, but if several different excitation pulses are combined. As already described above, a passive component can generate different excitation pulses one after the other, starting from different excitation states, or two or more different passive components can each emit an excitation signal one after the other. In principle, all of the combinations of excitation signals and measurement intervals described above are possible. A sequence of several excitation pulses or excitation signals and corresponding measurement intervals from one or more passive components then results in an excitation pattern, which is then preferably repeated periodically.

[0026] The described periodic implementation of the method according to the invention particularly advantageously enables an evaluation of the periodic excitation signal and the periodic measurement signal by means of Fourier analysis or other mathematical evaluations with regard to a frequency-dependent impedance behavior of the component to be examined.

[0027] According to a further aspect, the invention comprises a measuring arrangement for diagnosing a component to be examined, comprising a component to be examined that can be operated in an electrical circuit at a predetermined operating point for a predetermined measuring interval. The electrical circuit further comprises at least one passive component that can be brought into a predetermined excitation state at the beginning of the measuring interval in order to emit an excitation signal in the electrical circuit during the measuring interval. The measuring arrangement also comprises at least one measuring device for time-dependently measuring a measurement signal and / or for time-dependently measuring the excitation signal during the measuring interval, wherein the measurement signal results from a superposition of the excitation signal of the passive component and an operating signal of the component to be examined.In particular, a separate measuring device can be provided for measuring the measurement signal and a separate measuring device for detecting the excitation signal. However, both measurements can also be performed in a single device.

[0028] The measurement signal and the excitation signal are typically a current waveform and a voltage waveform in the circuit. Accordingly, the at least one measuring device is preferably configured to detect a voltage applied to the component under test and / or a current flow in the circuit as a function of time. Preferably, a current measuring device and a voltmeter are included in the circuit. The current and voltage measurements can also be performed in a single device. According to a preferred embodiment of the measuring arrangement according to the invention, the passive component is a capacitor whose predefined excitation state is charging with a predefined voltage.Preferably, the capacitor can be connected to the circuit by closing a first switch, and to a current and / or voltage source by closing a second switch. It can be charged to the predetermined voltage when the second switch is closed, and emit a discharge signal as an excitation signal when the second switch is open and the first switch is closed. The passive component is connected, for example, in parallel with the component under test.

[0029] It is also possible to use one or more capacitors as a voltage source or current sink. The charge or discharge curve of the capacitor(s) used when switching on or off from the circuit that keeps the cell under test operating serves as the excitation signal.

[0030] The passive component can also be a coil (inductance) or an electrical resistor. For an inductance, the predefined excitation state is, for example, a magnetization state. By applying an external magnetic field or by means of a second coil outside the circuit, the inductance's characteristics can be changed to assume a different excitation state and / or output a different excitation signal to the circuit.

[0031] For this purpose, the measurement setup can optionally include an arrangement for changing the characteristics of the passive component or the respective excitation state (e.g., magnetization / charge state). This arrangement includes, for example, a coil or an electromagnet or a temperature control device for adjusting the temperature of a passive component (e.g., a resistor).

[0032] In addition to the at least one passive component, the measuring arrangement according to the invention can comprise at least one further passive component, which can be connected into the circuit alternatively or alternately with the first passive component and preferably has a different characteristic than the first passive component. In particular, 3, 4, 5, or more passive components can also be present, each of which can be connected into the circuit one after the other.

[0033] Two identical passive components can also be provided, each of which can be alternately connected to the circuit and then returned to the excitation state. This allows excitation pulses to be delivered at shorter intervals, accelerating the measurement.

[0034] Furthermore, the measuring arrangement preferably comprises an evaluation device which allows the measured time-dependent excitation and measurement signals to be evaluated with regard to the impedance behavior, for example by means of a Fourier analysis, in particular with a fast Fourier transformation.

[0035] The method and measuring arrangement according to the invention make it possible to generate an excitation signal that is not fully symmetrical, but is applied periodically to the component under test. Cyclical excitation can be generated by cyclically connecting or disconnecting at least one passive component to the circuit under test.

[0036] According to a further aspect, the invention comprises a control device for carrying out the method according to the invention, which control device is configured to control a measuring arrangement according to the invention to carry out the method according to the invention.

[0037] The control device for implementing the method according to the invention preferably comprises suitable communication means for sending corresponding control or switching signals to the respective components of the measuring arrangement, in particular to the switch(es), to the current or voltage source, and to the at least one measuring device. The switches and current / voltage source, as well as the at least one measuring device, are preferably designed to be controllable via corresponding communication means, in particular electronically. However, the at least one measuring device can also be integrated into the control device.

[0038] Furthermore, according to a further aspect, the invention comprises an evaluation device configured to evaluate a measurement signal and excitation signal obtained using a method according to the invention and / or using a measuring arrangement according to the invention with regard to a temporal correlation between the excitation signal and the measurement signal. The evaluation device preferably comprises a computing unit with a processor and is configured to receive the time-dependent measurement and excitation signals via suitable communication means. For example, the first and second measuring devices can also be integrated into the evaluation unit. The evaluation device is thus preferably configured to evaluate the measurement and excitation signals with regard to an impedance behavior of the component to be examined.

[0039] The evaluation device and the described control device can be combined in a single device or can be present as separate devices. The evaluation device and control device are preferably provided as component(s) in the vehicle. They can, for example, be integrated into a fuel cell control system in a vehicle. Advantageously, appropriate measurements and analyses of the fuel cell can then be performed in the vehicle. This can, for example, be scheduled (e.g., at regular intervals) or occur when certain operating conditions change (e.g., during shutdown).

[0040] The invention is explained in more detail below with reference to the drawings, which schematically show:

[0041] Figure 1: a first embodiment of an inventive

[0042] measuring arrangement;

[0043] Figure 2: a flowchart for the sequence of the method according to the invention according to a first embodiment; Figure 3: an exemplary excitation signal according to a further preferred embodiment of the method according to the invention; and

[0044] Figure 4: a second embodiment of an inventive

[0045] Measuring arrangement.

[0046] In the first exemplary embodiment of a measuring arrangement according to the invention, as shown in Figure 1, a component 10 to be tested is connected to a load 16 in an electrical circuit 11. A first measuring device 46 is used to measure the electrical voltage applied to the component 10 to be tested. A second measuring device 47 is provided to measure the electrical current flowing in the circuit. A first passive component 14 can be connected in parallel with the component 10 to be tested in the circuit by means of a first switch 41. The first passive component 14 (for example a capacitor) can be connected to a (further) voltage source 45 via a second switch 44 in order to be charged with a voltage and thereby brought into a predetermined excitation state.

[0047] Figure 2 shows an example of the sequence of the method according to the invention in a preferred embodiment: In a first step 1, a fuel cell or a fuel cell stack is connected to a load (e.g. a battery, a vehicle drive, or an electrical load, etc.) at a constant load point as the component to be tested. In a second step 2, a capacitor of a suitable size (suitable capacitance and dielectric strength, charging and discharging characteristics) is brought into its predetermined excitation state as a passive component for excitation, i.e. pre-charged with a fixed reference voltage (e.g. via a 12V on-board network in the vehicle or 5V voltage level of a control unit, etc.). In step 3, in order to modulate the fuel cell current, the capacitor is then connected in parallel to the circuit comprising the fuel cell and the load for a predetermined measuring interval (typically at 200V, for example).The charging current (resulting from the capacitor's characteristics and the voltage difference to the fuel cell voltage) superimposes (in this case, increases) the cell's current load current. After the measurement interval has elapsed (the duration of which corresponds, for example, to 3-4 times the capacitor's time constant T), the capacitor is removed from the circuit (e.g., using a relay or transistor, etc.). Optionally, in a further step 4, its charge can then be discharged via a load at a lower voltage level or to the voltage source from step 2. The stored energy can preferably be used, for example, to operate a relevant consumer (e.g., control unit, 12V battery charger, lighting module, etc.). This minimizes the energy wasted from the cell under test, increasing the absolute efficiency of the system / vehicle.

[0048] The process can now optionally be repeated. To do this, the capacitor is preconditioned (preconditioned) in step 2. It can then be connected back into the circuit for the duration of a measurement interval in step 3. As a preferred variant, several capacitors can be alternately connected for excitation. This reduces the measurement time (or the waiting time until the component under test is re-excited) and increases the efficiency of the analysis.

[0049] Particularly preferably, several different capacitors (with different characteristics / time constants) can be connected sequentially or periodically alternating. This generates different excitation patterns that can be used as analogues to different excitation frequencies in the classical method.

[0050] Figure 3 shows an example of an excitation signal generated by three capacitors connected one after the other. In a first measuring interval 12, a first capacitor with a predetermined excitation state 15 is connected. The resulting excitation signal 13 has a specific characteristic with a first time constant. In a subsequent second measuring interval 22, a second capacitor 24 (shown in Figure 4) with an excitation state 25 is connected instead of the first capacitor 14. Subsequently, for a third measuring interval 32, a third capacitor 34 (shown in Figure 4) with a third excitation state 35 is connected instead of the second capacitor. The three capacitors (14, 24, 34) can have different excitation states (not shown here) or, for example, different time constants T. As a result, the characteristic of the excitation signal 13 differs between the three excitation pulses shown.Thus, the analysis of the measurement signal (in this example, the operating voltage of the fuel cell measured over the excitation time) results in different curves. In the illustrated embodiment, the duration of the first, second, and third measurement intervals (12, 22, 32) together corresponds to a period of 48. After that, the process can continue with the first capacitor 14 and measurement interval 12. The periodic measurement signal and excitation signal thus generated can then be analyzed for their phase response—and thus their impedance behavior—using Fourier analysis or other suitable mathematical analysis. Depending on the operating and functional status of the component under investigation, characteristic signal responses result, which allow interpretation regarding aging or "health" or the current operating status.

[0051] An embodiment of a measuring arrangement according to the invention with three passive components is shown as an example in Figure 4. The measuring arrangement according to Figure 4 differs from the arrangement shown in Figure 1 in that three different passive components 14, 24, 34 are provided, which can each be connected in parallel with the component to be tested alternatively, one after the other, or simultaneously in parallel using respective switches 41, 42, 43. Identical components are provided with the same reference numerals as in Figure 1. Parallel to the passive component 14, which can be connected to the circuit via switch 41, are the passive components 24, switchable via switch 42, and the passive component 34, switchable via switch 43. All three passive components 14, 24, 34 can be disconnected from the circuit using switch 40. They can be connected to the current or voltage source 45 via switch 44.The three passive components 14, 24, and 34 can be similar components with the same or different characteristics. However, different components are also possible. Preferably, the three passive components 14, 24, and 34 are alternately connected into the circuit 10 to each emit an excitation signal for the duration of a measurement interval 12, 22, 32. However, it can also be useful to connect two or more passive components simultaneously into the circuit 10 to emit a common excitation signal. Using switches 41, 42, and 43, any combination of the three passive components can be connected to the circuit. Thus, with a small number of passive components, different excitation signals can advantageously be generated, enabling a more precise analysis of the component under test. An evaluation device 50 enables the evaluation of the measured measurement signals and excitation signals.

[0052] List of reference symbols:

[0053] 10. Component to be examined

[0054] 11. electrical circuit

[0055] 12. first measurement interval

[0056] 13. Excitation signal

[0057] 14. first passive component

[0058] 15. Predefined first excitation state

[0059] 16. Last

[0060] 22. further (second) measurement interval

[0061] 24. second passive component

[0062] 25. Predefined further excitation state

[0063] 32. further (third) measurement interval

[0064] 34. third passive component

[0065] 35. third predefined excitation state

[0066] 40. Switch 1

[0067] 41 . Switch first passive component

[0068] 42. Switch second passive component

[0069] 43. Switch third passive component

[0070] 44. Switch 2

[0071] 45. Current / voltage source

[0072] 46. ​​first measuring device

[0073] 47. second measuring device

[0074] 48th period

[0075] 50. Control device / evaluation device

Claims

Patent claims 1 . Method for diagnosing a component (10) to be examined, comprising the steps of: a) operating the component (10) to be examined in an electrical circuit (11) at a predetermined operating point for a predetermined first measuring interval (12); b) and during this first measuring interval (12) detecting a measuring signal and an excitation signal (13) in the circuit (11) as a function of time, wherein the excitation signal (13) is a signal of a passive component (14) is in the circuit which is at the beginning of the first measuring interval (12) is in a predetermined first excitation state (15), and the measurement signal results from a superposition of the excitation signal (13) of the passive component (14) and an operating signal of the component to be examined (10).

2. Method for diagnosing a component to be examined (10) according to claim 1, with the further steps: c) switching on at least one further passive component (24, 34) after the expiry of the first measuring interval (12) for a predetermined further measuring interval (22, 32), wherein the at least one further passive component (24, 34) is in a predetermined further excitation state (25, 35) at the beginning of the further measuring interval (22, 32), and d) detecting the measuring signal and the excitation signal in the circuit as a function of time over the further measuring interval (22, 32).

3. Method for diagnosing a component to be examined (10) according to claim 2, wherein the passive component (14) and the at least one further passive component (24, 34) differ in their characteristics and / or each have different predetermined excitation states (15, 25, 35).

4. Method for diagnosing a component to be examined (10) according to one of the preceding claims, with the further steps: e) after expiry of the first and / or the further measuring interval (12, 22): bringing the passive component (14) into a further predetermined excitation state (25, 35) which differs from the first excitation state (15), and repeating steps a) and b), wherein the first passive component (14) is in the further excitation state (25, 35) which differs from the first excitation state (15) at the beginning of the further measuring interval (22, 32).

5. Method for diagnosing a component to be examined (10) according to one of the preceding claims, with the further steps: f) evaluating the measurement signal for an impedance behavior of the component to be examined (10) by evaluating a temporal correlation between the excitation signal (13) and the measurement signal.

6. Method for diagnosing a component to be examined (10) according to one of the preceding claims, wherein steps a) and b) and optionally additionally c) and d) and / or e) are carried out periodically.

7. Method for diagnosing a component to be examined (10) according to claim 6, wherein the time-dependent measurement signal is evaluated by means of Fourier analysis or other mathematical evaluation with regard to a frequency-dependent impedance behavior.

8. Measuring arrangement for diagnosing a component (10) to be examined, with a component (10) to be examined in a circuit (11) which can be operated for a predetermined measuring interval (12, 22) at a predetermined operating point, wherein the circuit (11) further comprises: - at least one passive component (14, 24) which can be brought into a predetermined excitation state (15, 25) at the beginning of the measuring interval (12, 22) in order to emit an excitation signal (13) in the circuit (11) during the measuring interval (12, 22), - At least one measuring device (46, 47) for measuring a measurement signal and / or for measuring the excitation signal (13) as a function of time during the measuring interval (12, 22), wherein the measurement signal results from a superposition of the excitation signal (13) of the passive component (14, 24) and an operating signal of the component (10) to be examined.

9. Measuring arrangement for diagnosing a component to be examined (10) according to claim 8, wherein the at least one measuring device (46, 47) is configured to detect a voltage applied to the component to be examined (10) and / or a current flow in the circuit (11) as a function of time.

10. Measuring arrangement for diagnosing a component to be examined (10) according to one of claims 8 to 9, wherein the passive component (14, 24) is a capacitor whose predetermined excitation state (15, 25) is a charge with a predetermined voltage.

11. Measuring arrangement for the diagnosis of a component to be examined (10) according to claim 10, wherein the capacitor (14) can be connected to the circuit (11) by closing a first switch (40) and can be connected to a current and / or voltage source (46) by closing a second switch (44) in order to be charged with a voltage when the second switch (44) is closed, and to emit an excitation signal (13) when the second switch (44) is open and the first switch (40) is closed.

12. Measuring arrangement for diagnosing a component to be examined (10) according to one of claims 8 to 11, wherein the at least one passive component (14, 24) is connected in parallel to the component to be examined (10).

13. Measuring arrangement for diagnosing a component to be examined (10) according to one of claims 8 to 9, wherein the passive component (14) is a coil whose predetermined excitation state is a predetermined magnetization state.

14. Measuring arrangement for diagnosing a component to be examined (10) according to claim 13, wherein the coil can be brought into a changed excitation state by applying an external magnetic field.

15. Measuring arrangement for diagnosing a component to be examined (10) according to one of claims 8 to 14, wherein the measuring arrangement has at least one further passive component (24, 34) which can be switched into the circuit (11) as an alternative to the first passive component (14) and has a characteristic different from the first passive component (14).

16. Control device (50) which is configured to control a measuring arrangement according to one of claims 8 to 15, to carry out a method according to one of claims 1 to 7.

17. Evaluation device (50) which is configured to evaluate a measurement signal obtained with a method according to one of claims 1 to 7 and / or with a measuring arrangement according to one of claims 8 to 15 with regard to an impedance behavior of the component (10) to be examined.

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