Apparatus for Characterizing the Electrical Resistance of a Measurement Object

Abstract

The invention relates to a measuring apparatus for characterizing the electrical resistance of a measurement object, comprising an electric energy source having two poles, a voltage measuring device having two measuring inputs, four connecting contacts for the connection of four contact electrodes, and a switching device for the variable electrical pairwise connection of each one of the poles and measuring inputs to each one of the connecting contacts, forming different wiring configurations, wherein the measuring device is configured to carry out at least two measuring sequences with different wiring configurations and to determine the series resistance of the measurement object by incorporating the current and voltage signals acquired in these wiring configurations.

Description

The invention relates to a device for characterizing the electrical resistance of a measurement object, in particular for determining the longitudinal resistance of a measurement object.

The characterization of the electrical resistance of measurement objects is important in many areas of industry and science, eg for the characterization of materials or electrical components. The electrical resistance is usually not a scalar quantity, but a tensor with several different components. The resistance tensor combines the spatial orientation of the current with the spatial orientation of the voltage. The resistance can be characterized, for example for material layers, by the longitudinal resistance and the transverse resistance. For a current that runs within a layer (and parallel to the layer), the longitudinal resistance characterizes the quotient between the current and the voltage present in parallel with this current, and the transverse resistance characterizes the quotient between the current and the current within the layer (and parallel to the layer) perpendicular to this current voltage. In the present case, the terms resistance, current and voltage refer to the electrical resistance, the electrical current or the electrical voltage, unless something else is apparent from the context. The components of the resistance tensor are also referred to as resistance components.

The individual components of the resistance tensor can be determined, for example, by producing a sample with such a sample geometry for the determination of each individual tensor component and measuring electrically in such a circuit geometry that all components except the individual component to be determined are negligible for the present sample and circuit geometry. The sample used to determine an individual component can be structured, for example, and electrically connected in a four-point measurement such that because of the predetermined current direction and the predetermined voltage tap positions, the resistance is essentially given solely by the individual component to be determined. For example, in the case of a sample in the form of a right-angled cross with four cross arms, in which a current is passed through two opposing arms, the influence of the longitudinal resistance is zero or negligibly small, so that by detecting the resulting voltage between the two opposing arms, the voltage of the transverse resistance can be determined.

Thus, each individual component of the resistance tensor can be determined by means of a sample having a corresponding sample geometry. In this case, to determine different components, several samples or measurement objects with different sample geometries must be produced, which entails a corresponding expenditure of time and materials. In addition, due to the limited accuracy of the sample geometries that can be produced, the resistance components determined are also subject to a corresponding inaccuracy. Finally, with this method, different resistance components can only be determined for different sample geometries or sample areas (and not for the same sample or one and the same sample area), which results in further inaccuracies.

The invention is intended to provide a device by means of which the electrical resistance, in particular the longitudinal resistance, of a measurement object can be easily characterized with high accuracy. The device can be designed, for example, for the simultaneous determination of the longitudinal and transverse resistance of the measurement object.

According to the invention, a device (hereinafter also referred to as measuring device) for characterizing the electrical resistance of a measuring object is provided. The measuring device can be designed, for example, for determining different components of the resistance tensor, for example for determining the longitudinal resistance and/or the transverse resistance of the measurement object. The longitudinal resistance is also referred to as series resistance, and the transverse resistance is also referred to as cross resistance.

The measurement object is preferably designed such that its extent in two of the three spatial dimensions is greater than its extent in the third spatial dimension. In other words, the measurement object is preferably a material layer whose length and width is greater than its thickness. Such a material layer is therefore substantially two-dimensional or can be assumed to be two-dimensional.

The measuring device has an electrical power source for providing an electric current as an input current. The power source has a first terminal and a second terminal, the input current being provided between these two electrical terminals. The terminals form the connection points of the power source and are therefore also referred to as the first and second connection terminals. The power source may be an electrical power source, eg, a power source for providing DC or AC power. Alternatively, the power source may be an electrical voltage source, eg a voltage source for providing a DC voltage or AC voltage.

The measuring device also has a voltage measuring device for detecting or measuring an electrical voltage. The voltage measuring device has a first and a second measuring input and is designed to detect the voltage present between these two measuring inputs as an output voltage.

The measuring device has at least four connection contacts, wherein each of the connection contacts is provided for electrical connection to a contact electrode to form an electrical connection between the connection contact and the contact electrode, and wherein the contact electrodes are provided for electrically contacting the measurement object. The measuring device thus has at least one first connection contact for connecting (ie, electrically linking) a first contact electrode thereto, a second connection contact for connecting a second contact electrode thereto, a third connection contact for connecting a third contact electrode thereto, and a fourth connection contact for connecting a fourth contact electrode thereto, wherein the first, second, third and fourth contact electrodes are provided for electrically contacting the measurement object. The measuring device can be formed by means of the connection contacts, for example for forming a detachable connection (eg a detachable plug connection) between the connection contacts and the contact electrodes. The measuring device can thus have four connection contacts for forming a detachable electrical connection to one respective contact electrode each. The connection contacts can be designed, for example, as connection sockets.

The measuring device can accordingly have at least four electrodes (also referred to as contact electrodes) which are provided for electrically contacting the measurement object. The measuring device can thus have at least one first, one second, one third and one fourth contact electrode. Each of the contact electrodes has an exposed contact point provided for contacting the measurement object. When the measuring device is used as intended, the first contact electrode is connected to the first connection contact to form an electrical connection, the second contact electrode is connected to the second connection contact to form an electrical connection, the third contact electrode is connected to the third connection contact to form an electrical connection, and the fourth contact electrode is connected to the fourth connection contact to form an electrical connection. In the intended use of the measuring device all the contact electrodes are also in physical contact with the measurement object, wherein the contact point of each contact electrode is in physical contact with the measurement object.

Furthermore, the measuring device has a switching device. For variable pairwise electrical connection, the switching device is formed from respectively the first terminal of the power source, the second terminal of the power source, the first measuring input of the voltage measuring device and the second measuring input of the voltage measuring device on the one hand with respectively the first connection contact, the second connection contact, the third connection contact and the fourth connection contact on the other hand. When the measuring device is used as intended, each of the connection contacts is connected to the respective contact electrode, so that the measuring device uses the switching device respectively for variable pairwise electrical connection of the first terminal, the second terminal, the first measuring input and the second measuring input of respectively the first contact electrode, the second contact electrode, the third contact electrode and the fourth contact electrode. Thus by means of the switching device, different electrical connection configurations of the contact electrodes can be realized or formed, wherein in each case the first terminal is electrically connected with one of the four contact electrodes, the second terminal with one of the four contact electrodes (in particular with a different one of the four contact electrodes than the first terminal), the first measuring input with one of the four contact electrodes (in particular with a different one of the four contact electrodes than the first terminal and the second terminal), and the second measuring input with one of the four contact electrodes (in particular with another of the four contact electrodes as the first terminal, the second terminal and the first measuring input). The switching device is designed for the variable pairwise electrical connection of said elements, ie using the switching device, at least two different connection configurations can be formed.

However, it can also be provided that the switching device is designed to realize more than two connection configurations, eg to realize all possible connection configurations. It can be provided, for example, that the switching device is designed such that the first terminal can be connected to any one of the four connection contacts (and thus to any of the four contact electrodes), the second terminal to be connected to any one of the three remaining connection contacts (and thus to any one of the three remaining contact electrodes), the first measurement input can be connected to any one of the two remaining connection contacts (and thus to any of the two remaining contact electrodes), and the second measurement input to the sole remaining connection contact (and thus, with the only remaining contact electrode). In this case, “connect” or “connection” refers to an electrical connection or an electrical linkage, that is to say the formation of an electrically conductive connection, unless the context dictates otherwise.

During the intended use of the measuring device, the connection contacts in are in contact with the contact electrodes and the contact electrodes are in contact with the measurement object, wherein a current flow is generated in the measurement object by means of the electrical power source. The measuring device is designed in such a way that the input current flowing between the two connection contacts or contact electrodes, which are connected to the two terminals of the power source, can be detected by it as an input current signal. The input current signal describes the input current as a function of time, so that the input current-time characteristic is detected by the measuring device as an input current signal.

Due to the introduced input current, a voltage is produced between the other two contact electrodes (that is to say the contact electrodes connected to the two measuring inputs of the voltage measuring device). By means of the voltage measuring device, the voltage present between the two connection contacts or contact electrodes, which are connected to the two measuring inputs of the voltage measuring device, can be detected by the measuring device as the output voltage signal. The output voltage signal then describes the output voltage as a function currently, so that the output voltage waveform is detected as an output voltage signal by the measuring device using the voltage measuring device.

Because different switching configurations of the contact electrodes can be formed by means of the switching device, the input current signal and the output voltage signal can be detected by means of the measuring device for different switching configurations, and based on the plurality of input current signals and the plurality of output voltage signals, the electrical resistance or resistance tensor of the measuring object can be characterized, eg determined. Accordingly, the measuring device may be configured to characterize different resistance components based on the input current signals and output voltage signals detected for different circuit configurations.

The measuring device is designed to perform at least a first and a second measurement sequence with different connection configurations as follows. In this regard, in particular the switching device for variable pairwise electrical connection of each one of the first terminal, the second terminal, the first measuring input and the second measuring input on the one hand with one of the four connection contacts (and thus with one of the four contact electrodes) on the other hand, is designed such that the connection configurations required for the first and second measurement sequences can be realized by the measuring device. The first and second measurement sequences can be performed in any order.

In the first measurement sequence, by means of the switching device, the first connection contact (and thus, when the measuring device is used as intended, the first contact electrode) is electrically connected to one of the two terminals of the power source, the second connection contact (or the second contact electrode) is electrically connected to the other of the two terminals of the power source, the third connection contact (or the third contact electrode) is electrically connected to one of the two measuring inputs of the voltage measuring device, and the fourth connection contact (or the fourth contact electrode) is electrically connected to the other of the two measuring inputs of the voltage measuring device. Accordingly, in the first measurement sequence, the input current is present between the first and the second connection contact (or between the first and the second contact electrode) and is detected by the measuring device as a first input current signal. By means of the voltage measuring device, the voltage present between the third and fourth connection contact (or between the third and fourth contact electrode) is detected as the first output voltage signal in the first measurement sequence.

In the second measurement sequence, the third connection contact (or the third contact electrode) is electrically connected with one of the two terminals of the power source, the fourth connection contact (or the fourth contact electrode) is electrically connected with the other of the two terminals of the power source, the first connection contact (or the first contact electrode) is electrically connected by means of the switching device to one of the two measuring inputs of the voltage measuring device, and the second connection contact (or the second contact electrode) is electrically connected to the other of the two measuring inputs of the voltage measuring device. Accordingly, in the second measuring sequence, the input current is present between the third and the fourth connection contact (or between the third and the fourth contact electrode) and is detected by the measuring device as a second input current signal. In the second measuring sequence, the voltage present between the first and second connection contact (or between the first and second contact electrode) is detected as the second output voltage signal by means of the voltage measuring device.

The measuring device is formed, for example by means of an appropriately designed evaluation device, for determining the longitudinal resistance and/or the transverse resistance of the measurement object, including the first and the second input current signal and the first and the second output voltage signal. On the basis of the detected input current signals and output voltage signals, the determination of the longitudinal resistance and also the simultaneous determination of the longitudinal and the transverse resistance is made possible for one and the same measurement object, whereby the uncomplicated determination of these resistance components with high accuracy is made possible. In particular, the longitudinal and the transverse resistance can be determined simultaneously without changing the sample or the measurement object.

The measuring device may for example be designed such that—in the first measuring sequence, the first connection contact (or the first contact electrode) is electrically connected to the first terminal, the second connection contact (or the second contact electrode) is electrically connected to the second terminal, the third connection contact (or the third contact electrode) is electrically connected to the first measuring input and the fourth connection contact (or the fourth contact electrode) is electrically connected to the second measuring input, and

• • in the second measuring sequence, the third connection contact (or the third contact electrode) is electrically connected to the first terminal, the fourth connection contact (or the fourth contact electrode) is electrically connected to the second terminal, the second connection contact (or the second contact electrode) is electrically connected to the first measuring input and the first connection contact (or the first contact electrode) is electrically connected to the second measuring input, or
  • in the second measuring sequence the fourth connection contact (or the fourth contact electrode) is electrically connected to the first terminal, the third connection contact (or the third contact electrode) is electrically connected to the second terminal, the first connection contact (or the first contact electrode) is electrically connected to the first measuring input and the second connection contact (or the second contact electrode) is electrically connected to the second measuring input.

By this choice of connection configurations in the first measurement sequence the same handedness between introduced current and tapped voltage before as in the second measurement sequence, ie the same relative orientation of the introduced current to the tapped voltage (this orientation can be illustrated by the orientation of the connection direction which points from the contact electrode connected to the first terminal to the contact electrode connected to the second terminal, relative to the connection direction which points from the contact electrode connected to the first measuring input to the contact electrode connected to the second measuring input). By having the same handedness in the first measurement sequence as in the second measurement sequence, high-precision detection of the longitudinal and/or transverse resistance can be carried out in an uncomplicated manner.

According to one embodiment, the measuring device is designed to determine a first resistance value from the first output voltage signal and the first input current signal and to determine a second resistance value from the second output voltage signal and the second input current signal. The manner of calculating the resistance values for different wiring configurations will be explained in more detail below.

For a given circuit configuration, the resistance value is determined from the output voltage signal present in this circuit configuration and the input voltage signal present in this circuit configuration. In the following, (i, j, k, l) designates the wiring configuration in which the first terminal of the power source is electrically connected to the ith connection contact (or to the ith contact electrode), the second terminal of the power source is electrically connected to the jth connection contact (or to the j-th contact electrode), the first measuring input of the voltage measuring device is electrically connected to the k-th connection contact (or to the k-th contact electrode), and the second measuring input of the voltage measuring device is electrically connected to the l-th connection contact (or to the l-th contact electrode), so that when the measuring device is used properly, the input current l_ij flows between the i-th and the j-th contact electrode and the output voltage U_kl is tapped between the k-th and the l-th contact electrode. The resistance value present in the wiring configuration (i, j, k, l) is denoted by R_ijkl.

In the case where the input current is a direct current, for the wiring configuration (i, j, k, l), the resistance value R ijkl is given by the ratios of the output voltage U kl, which is present between the k-th contact electrode and the I-th contact electrode (and thus between the k-th connection contact and the I-th connection contact), and the input current I ij, which flows between the i-th contact electrode and the j-th contact electrode (and thus between the i-th connection contact and the j-th connection contact), so that the resistance value R ijkl can be written as

R _ijkl =U _kl /I _ij  (1)

In the event that the input current is an (eg periodic) alternating current, the input current l_ij(t) present between the i-th and the j-th connection contacts (and thus also between the ith and the jth connection contacts) may be written as a Fourier series of form

I _ij(t)=Σ_n I_ijⁿ·sin(n·ω·t+φ_ijⁿ)  (2)

and the output voltage U_kl(t) present between the k-th and the l-th contact electrodes (and thus also between the k-th and the l-th connection contacts) may be written in the form of a Fourier series

U _kl(t)=Σ_n U_klⁿ·sin(n·ω·t+φ_klⁿ)  (3)

where ω w denotes the fundamental frequency, t denotes the time, n is a natural number, with I_ijⁿ or U_klⁿ designated as the amplitude of the respective frequency component at the frequency n·ω, and with φ_ijⁿ or φ_klⁿ designated as a phase fraction of the respective frequency component (which indicates the initial phase at time t=0).

With these designations, the resistance value R_ijkl for the wiring configuration (i, j, k, l) results from the frequency components of the Fourier series belonging to n=1 for l_ij(t) and U_kl(t), wherein the resistance value R_ijkl becomes a complex resistance value of the form

R _ijkl =Re(R_ijkl)+i·Im(R_ijkl)  (4)

where Re(R_ijkl) denotes the real part and Im (R_ijkl) denotes the imaginary part, and where the real part is given by

Re(R_ijkl)=U_kl¹·cos(φ_ij¹−φ_kl¹)/I_ij¹  (5)

and the imaginary part is given by

Im(R_ijkl)=U_kl¹·sin(φ_ij¹−φ_kl¹)/I_ij¹  (6)

Thus, if the input current is an alternating current, the resistance elements R_ijkl are thus complex resistive elements and are therefore also referred to as impedance elements.

Thus, the resistance elements R_ijkl result from the frequency components corresponding to the fundamental frequency ω of the output voltage signal U_kl(t) and the input current signal l_ij(t), which are also referred to as fundamental frequency components. The real part of the resistance element R_ijkl results from the quotient of the amplitude U_kl¹ of the fundamental frequency portion of the output voltage signal and the amplitude I_ij¹ of the fundamental frequency component of the input current signal, this quotient being multiplied by the cosine of the difference between the initial phase φ_ij¹ of the fundamental frequency component of the input current signal and the initial phase φ_kl¹ of the fundamental frequency portion of the output voltage signal. The real part of the resistance element R_ijkl results from the quotient of the amplitude U_kl¹ of the fundamental frequency portion of the output voltage signal and the amplitude I_ij¹ of the fundamental frequency component of the input current signal, this quotient being multiplied by the sine of the difference between the initial phase φ_ij¹ of the fundamental frequency component of the input current signal and the initial phase φ_kl¹ of the fundamental frequency portion of the output voltage signal.

The measuring device can be designed by means of the above-explained first and second measurement sequence, for example, to determine R₁₂₃₄ as the first resistance element and R₃₄₂₁ or R₄₃₁₂ as a second resistance element.

The (average or half) sum of the first resistance value and the second resistance value is proportional to the transverse resistance of the measurement object and thus forms a measure of the transverse resistance. The (average or half) difference between the first resistance value and the second resistance value is proportional to the longitudinal resistance of the measurement object and thus forms a measure of the longitudinal resistance. The respective proportionality factors result from the respective wiring geometry and can be determined, for example, on the basis of the known geometry of the measurement object or by measurement on a reference sample with known resistance tensor and comparison of the measurement result with the known resistance components.

Accordingly, it can be provided that the measuring device is designed to determine the longitudinal resistance and/or the transverse resistance of the measurement object based on the first resistance value and the second resistance value. It can be provided in particular that the measuring device is designed to determine the longitudinal resistance of the measurement object based on the difference between the first resistance value and the second resistance value and/or to determine the transverse resistance of the measurement object based on the sum of the first resistance value and the second resistance value.

According to the above embodiment, therefore, according to equation (1) for the direct current case or according to equations (2) to (6) for the alternating current case, for example, the first resistance value can be determined as R₁₂₃₄ and the second resistance value can be determined as R₃₄₂₁, wherein the series resistance or longitudinal resistance R_long of the measurement object, eg by means of

R _long =P ₁·(R₁₂₃₄−R₃₄₂₁)/2˜(R₁₂₃₄−R₃₄₂₁)  (7)

and the transverse resistance or transversal resistance R_trans of the measurement object, for example by means of

R _trans =P ₂·(R₁₂₃₄+R₃₄₂₁)/2˜(R₁₂₃₄+R₃₄₂₁)  (8)

where P₁ and P₂ are proportionality factors, and where the character “˜” represents the proportionality sign. The measuring device can thus be designed, for example by means of an appropriately designed evaluation device, for determining the longitudinal resistance R_long and/or the transverse resistance R_trans on the basis of equations (7) or (8) in conjunction with equation (1) for the DC case and with the equations (2) to (6) for the AC case.

According to a further embodiment, the measuring device is designed, in addition to the first and second measuring sequence, for performing at least one third and fourth measuring sequence with different connection configurations as follows. In this regard, in particular the switching device is designed for variable pairwise electrical connection of respectively one of the first terminal, the second terminal, the first measuring input and the second measuring input on one hand with one of the four connection contacts (and thus with one of the four contact electrodes) on the other hand, such that the connection configurations of the measuring device required for the first, second, third and fourth measurement sequence can be realized. The first, second, third and fourth measurement sequences can be performed in any order.

According to this embodiment, in the first measuring sequence by means of the switching device, the first connection contact (and thus, when the measuring device is used as intended, the first contact electrode) is electrically connected with the first terminal of the power source, the second connection contact (or the second contact electrode) is electrically connected to the second terminal of the power source, the third connection contact (or the third contact electrode) is electrically connected to the first measuring input of the voltage measuring device, and the fourth connection contact (or the fourth contact electrode) is electrically connected to the second measuring input of the voltage measuring device, wherein the input current is present between the first and the second contact electrode (and thus between the first and second connection contact) and is detected as a first input current signal (l₁₂), and wherein by means of the voltage measuring device the voltage generated between the third and the fourth contact electrode (and thus between the third and fourth connection contact) is detected as the first output voltage signal (U₃₄).

According to this embodiment, in the second measuring sequence by means of the switching device, the third connection contact (or the third contact electrode) is electrically connected to the first terminal of the power source, the fourth connection contact (or the fourth contact electrode) is electrically connected to the second terminal of the power source, the second connection contact (or the second contact electrode) is electrically connected to the first measuring input of the voltage measuring device, and the first connection contact (or the first contact electrode) is electrically connected to the second measuring input of the voltage measuring device, wherein the input current is present between the third and the fourth contact electrode (and thus between the third and fourth connection contact) and is detected as a second input current signal (l₃₄), and wherein by means of the voltage measuring device the voltage generated between the first and the second contact electrode (and thus between the first and second connection contact) is detected as a second output voltage signal (U₂₁).

In the third measuring sequence, by means of the switching device the second connection contact (or the second contact electrode) is electrically connected to the first terminal of the power source, the first connection contact (or the first contact electrode) is electrically connected to the second terminal of the power source, the fourth connection contact (or the fourth contact electrode) is electrically connected to the first measuring input of the voltage measuring device, and the third connection contact (or the third contact electrode) is electrically connected to the second measuring input of the voltage measuring device, wherein the input current is present between the second and first contact electrode (and thus between the second and first connection contact) and is detected as the third input current signal (l₂₁), and wherein by means of the voltage measuring device the voltage between the fourth and the third contact electrode (and thus between the fourth and third connection contact) is detected as the third output voltage signal (U₄₃).

In the fourth measuring sequence, the fourth connection contact (or the fourth contact electrode) is electrically connected to the first terminal of the power source by means of the switching device, the third connection contact (or the third contact electrode) is electrically connected to the second terminal of the power source, the first connection contact (or the first contact electrode) is electrically connected to the first measuring input of the voltage measuring device, and the second connection contact (or the second contact electrode) is electrically connected to the second measuring input of the voltage measuring device, wherein the input current is present between the fourth and the third contact electrode (and thus between the fourth and the third connection contact) and is detected as the fourth input current signal (l₄₃), and wherein by means of the voltage measuring device, the voltage generated between the first and second contact electrode (and thus between the first and second connection contact) is detected as the fourth output voltage signal (U₁₂).

According to this embodiment, the measuring device can be designed, for example, by means of a suitably designed evaluation device, for determining the longitudinal resistance and/or the transverse resistance of the measurement object including the first, second, third and fourth input current signal as well as the first, second, third and fourth output voltage signal.

According to one embodiment, the measuring device is designed for determining a first resistance value from the first output voltage signal and the first input current signal, a second resistance value from the second output voltage signal and the second input current signal, a third resistance value from the third output voltage signal and the third input current signal, and a fourth resistance value from the fourth output voltage signal and the fourth input current signal.

It can be provided, for example, that the measuring device according to equation is designed (1) in the DC case or according to equations (2) to (6) in the AC case for determining the first resistance value R₁₂₃₄ from the first output voltage signal and the first input current signal, the second resistance value R₃₄₂₁ from the second output voltage signal and the second input current signal, the third resistance value R₂₁₄₃ from the third output voltage signal and the third input current signal, and the fourth resistance value R₄₃₁₂ from the fourth output voltage signal and the fourth input current signal.

The (average or quarter) sum of the first, second, third and fourth resistance values is proportional to the transverse resistance of the measurement object and thus forms a measure of the transverse resistance. The (average or quarter) sum at which the two resistance values R₁₂₃₄ and R₂₁₄₃ for the input current between the first and the second contact electrode are entered with a positive sign and the two resistance values R₃₄₂₁ and R₄₃₁₂ for the input current between the third and the fourth contact electrode are entered with a negative sign (also referred to as “alternating sum”) is proportional to the longitudinal resistance of the measurement object and thus forms a measure of the longitudinal resistance. The respective proportionality factors result from the respective wiring geometry and can be determined, for example, on the basis of the known geometry of the measurement object or by measurement on a reference sample with known resistance tensor and comparison of the measurement result with the known resistance components.

Accordingly, it can be provided that the measuring device is designed (eg by means of an appropriately designed evaluation device) for determining the longitudinal resistance and/or the transverse resistance of the measurement object based on the first, second, third and fourth resistance values. It can be provided in particular that the measuring device is designed to determine the transverse resistance of the measurement object based on the sum of the first, the second, the third and the fourth resistance values. In addition, it can be provided that the measuring device is designed to determine the longitudinal resistance of the measurement object based on the alternating sum of the first, the second, the third and the fourth resistance values.

According to the notation explained above, the measuring device can thus be designed to determine the longitudinal resistance R_long and/or the transverse resistance R_trans on the basis of the following equations:

R _long =P ₁·(R₁₂₃₄−R₃₄₂₁+R₂₁₄₃−R₄₃₁₂)/4˜(R₁₂₃₄−R₃₄₂₁+R₂₁₄₃−R₄₃₁₂)  (9)

R _trans =P ₂·(R₁₂₃₄+R₃₄₂₁+R₂₁₄₃+R₄₃₁₂)/4˜(R₁₂₃₄+R₃₄₂₁+R₂₁₄₃+R₄₃₁₂)  (10)

where P₁ and P₂ are proportionality factors.

In the given connection configurations—even with the formation of the input current as AC—the assignment of the respective contact electrode to the respective terminal or measuring input is to be noted, for example, wherein R_ijkl is not identical to R_jikl or R_ijkl. This ensures that the same handedness between introduced current and tapped voltage is present in all measurement sequences, so that highly accurate detection of the longitudinal and/or transverse resistance can be carried out in a straightforward manner. The input current may be a direct current or an alternating current. The consideration of four resistance values allows a higher measurement accuracy, both in the case that the input current is a direct current and in the case that the input current is an alternating current.

The measuring device may be configured to store the detected input current signals (ie, the detected input current time courses) and the detected output voltage signals (ie, the detected output voltage time courses) in a data memory such that these detected signals are subsequently available for use as raw data for determining different components of the resistance tensor of the measurement object. The measuring device can thus be designed in particular for storing the first, second, third and/or fourth input current signal as well as for storing the first, second, third and/or fourth output voltage signal by means of a data memory. As a result, the longitudinal resistance and/or the transverse resistance of the measurement object can be determined by the measuring device, for example, based on the stored signals by means of different calculation types. It can be designed, for example, to analyse the stored input current signals and/or output voltage signals by means of a Fourier transform (see below).

Alternatively or additionally, the measuring device for storing the determined resistance values (eg the first, second, third and/or fourth resistance value) may be formed in a data memory so that these determined resistance values are subsequently available as raw data for determining different components of the resistance tensor of the measurement object. As a result, for example, the longitudinal resistance and/or the transverse resistance of the measurement object can be determined by the measuring device based on the stored resistance values by means of different calculation types.

The measuring device is designed to detect the electric current flowing between the first terminal and the second terminal of the electric power source as an input current signal. In addition, the measuring device for detecting the electrical voltage present between the first measuring input and the second measuring input of the voltage measuring device is designed as an output voltage signal. When configuring the input current signal as an alternating current signal, the measuring device can be constructed, for example, by means of an appropriately designed evaluation device for processing or analysing the input current signals and/or output voltage signals by means of a Fourier transform. The measuring device can also be designed to characterize the longitudinal resistance and/or the transverse resistance of the measurement object based on the Fourier-transformed input current signals and/or the Fourier-transformed output voltage signals.

According to one embodiment, the measuring device is designed to Fourier-transform the output voltage signal and/or Fourier-transform the input current signal. Accordingly, the measuring device is designed to Fourier-transform the detected input current signals (eg the first, second, third or fourth input current signal) and/or output voltage signals (eg the first, second, third or fourth output voltage signal); preferably both the input current signals and the output voltage signals are subjected to a Fourier transform.

The input current signal describes the variation of the input current as a function of time and the output voltage signal describes the variation of the output voltage as a function of time, so that these are time signals. By means of the Fourier transform (also referred to as Fourier analysis), the respective time signal is assigned a frequency spectrum which describes which frequencies are included at which proportions in the original time signal. The measuring device can thus be designed in such a way that it transforms the input current signal into a Fourier-transformed input current signal according to equation (2), and/or transforms the output voltage signal into a Fourier-transformed output voltage signal according to equation (3) by means of the Fourier transform. By means of the Fourier analysis, for example, distortions of the signal profiles (in particular of the detected voltage profiles) can be detected, as a result of which, for example, underlying physical effects can be characterized. In particular, the harmonic distortions of the output voltage signals provide information about effects that determine the electrical properties, and effects with only slight influence can also be detected. By means of the Fourier-transformed signals, it is thus possible to obtain further information about the resistance of the measurement object, for example via the current dependence of the electrical resistance.

By means of the Fourier transform, for example, an analysis of the nonlinear electrical behaviour of the measurement object can be carried out. If the measurement object has a nonlinear electrical resistance, its resistance changes as a function of the current flow, so that, for example, with a sinusoidal input current, the resistance at the tips of the sine wave can have a higher or lower value than at the zero crossings of the sine wave. These and similar non-linear electrical properties lead to non-linear distortions of the sine wave or in the output voltage signal. This results in harmonic distortions in the Fourier-transformed output voltage signal, so that, for example, in the case of a sinusoidal input current signal having the fundamental frequency ω, the Fourier-transformed output voltage signal also contains portions at integer multiples n·ω of of this fundamental frequency (portions whose frequency n·ω is an integer multiple of the fundamental frequency ω, also referred to as harmonics, and where n is a natural number denoting the order of harmonics at the frequency n·ω).

It can be provided, for example, that the measuring device is designed based on the Fourier-transformed input current signals and/or the Fourier-transformed output voltage signals for determining the longitudinal resistance and/or the transverse resistance of the measurement object for different frequencies or harmonic orders, whereby the dependence of the longitudinal resistance or the transverse resistance on the strength of the electric current is detectable.

The input current may be in the form of an alternating current, eg in the form of a harmonic alternating current (ie an alternating current following a sine function). When the input current signal is given by a harmonic alternating current at a given fundamental frequency, the output voltage signal may have components at that fundamental frequency as well as at integer multiples of this fundamental frequency. When the input current signal is composed of multiple harmonic alternating currents having different fundamental frequencies, the output voltage signal may have shares in these different fundamental frequencies as well as at integer multiples of these different fundamental frequencies. By comparing the frequency spectra of the input current signals and the output voltage signals, conclusions can be drawn about the resistance of the measurement object and its causes. In particular, the measuring device may be designed for determining the longitudinal and/or transverse resistance of the measurement object for different frequencies or harmonic orders based on the Fourier-transformed input current signals and the Fourier-transformed output voltage signals.

For example, if the input current signal is a harmonic alternating current with the fundamental frequency ω, the input current signal may be written in the form

I _ij(t)=A_ij·sin(ω·t)  (11)

and the output voltage signal in the form

U _kl(t)=Σ_n B_klⁿ·sin(n·ω·t+φ_klⁿ)  (12)

(see also equations (2) and (3)).

Thus, analogously to equations (4) to (6), harmonic-dependent complex resistance elements R_ijklⁿ of the form

R _ijkl ⁿ =Re(R_ijklⁿ)+i·Im(R_ijklⁿ)  (13)

may be formed, where Re (R_ijklⁿ) denotes the real part and Im (R_ijklⁿ) denotes the imaginary part, and wherein the real part is given by

Re(R_ijklⁿ)=B_klⁿ·cos(−φ_klⁿ)/A_ij  (14)

and the imaginary part is given by

Im(R_ijklⁿ)=B_klⁿ·sin(−φ_klⁿ)/A_ij  (15)

According to one embodiment, the measuring device is thus designed such that it provides an input current in the form of a harmonic alternating current with an input current amplitude (A_ij) and an input current frequency (ω), wherein the frequency of the harmonic input current is also referred to as the fundamental frequency. It can be provided that the amplitude and the fundamental frequency of the input current from the power source are predetermined or detected. However, it can also be provided that the measuring device is designed to Fourier-transform the input current signals and determine the input current amplitude and the fundamental frequency from the Fourier-transformed input current signals. According to this embodiment, the measuring device is further configured to Fourier-transform the output voltage signals and to detect the individual frequency components of each Fourier-transformed output voltage signal, each of these frequency components being represented by an amplitude (B_klⁿ), a phase (φ_klⁿ) and a frequency (ω_n=n·ω) (wherein the frequency ω_n corresponds to the fundamental frequency or an integer multiple thereof).

The measuring device can also be used to determine the first, second, third and/or fourth resistance element present for a given harmonic order n R_ijklⁿ formed according to the equations (11) to (15). Accordingly, the resistance elements associated with the harmonic order n result R_ijkl from the frequency components corresponding to the fundamental frequency ω of the input current signal l_ij(t) and the frequency components of the output voltage signal U_kl(t) corresponding to the harmonic frequency ω_n=n·ω. The real part of the resistance element R_ijklⁿ results from the quotient of the amplitude B_klⁿ of the respective harmonic component of the output voltage signal and the amplitude A_ij of the fundamental frequency component of the input current signal, this quotient being multiplied by the cosine of the negative initial phase φ_klⁿ of the harmonic content of the output voltage signal. The imaginary part of the resistance element R_ijklⁿ results from the quotient of the amplitude B_klⁿ of the respective harmonic component of the output voltage signal and the amplitude A_ij of the fundamental frequency component of the input current signal, this quotient being multiplied by the sine of the negative initial phase φ_klⁿ of the harmonic content of the output voltage signal.

The measuring device can also be designed analogously to the embodiments described with reference to equations (7) to (10) for determining the longitudinal and/or transverse resistance present for a plurality of different harmonic orders n.

It can be provided, for example, that the measuring device for determining the longitudinal resistance and/or transverse resistance of the measuring object is formed based on the first and second resistance values existing for the predetermined harmonic order n. It can be provided, in particular, that the measuring device is designed to determine the longitudinal resistance of the measurement object existing for the given harmonic order based on the difference between the first and second resistance values present for the predetermined harmonic order, and/or that the measurement device for determining the transverse resistance of the measurement object existing for a given harmonic order is formed based on the sum of the first and second resistance values existing for the predetermined harmonic order.

Accordingly, the measuring device can eg (analogous to the equations (7) and (8)), based on the harmonic-dependent resistance elements R_ijklⁿ, be designed for determining the harmonic-dependent longitudinal resistance R_longⁿ and/or the harmonic-dependent transverse resistance R_transⁿ according to the following equations:

R _long ⁿ =P ₁·(R₁₂₃₄ⁿ−R₃₄₂₁ⁿ)/2˜(R₁₂₃₄ⁿ−R₃₄₂₁ⁿ).  (16)

R _trans ⁿ =P ₂·(R₁₂₃₄ⁿ+R₃₄₂₁ⁿ)/2˜(R₁₂₃₄ⁿ+R₃₄₂₁ⁿ).  (17)

Alternatively, it can be provided that the measuring device for determining the longitudinal resistance and/or transverse resistance of the measuring object for a predetermined harmonic order n is designed based on the first, second, third and fourth resistance values existing for the predetermined harmonic order. It can be provided, in particular, that the measuring device is designed to determine the longitudinal resistance of the measurement object present for a given harmonic order based on the alternating sum of the first, second, third and fourth resistance values existing for the given harmonic order. Alternatively or additionally, it can be provided that the measuring device is designed to determine the transverse resistance of the measurement object present for a given harmonic order based on the sum of the first, second, third and fourth resistance values present for the predetermined harmonic order.

Accordingly, the measuring device can eg (analogous to the equations (9) and (10)) be formed based on the harmonic-dependent resistance elements R_ijklⁿ for determining the harmonic-dependent longitudinal resistance R_longⁿ and/or the harmonic-dependent transverse resistance R_transⁿ according to the following equations:

R _long ⁿ =P ₁·(R₁₂₃₄ⁿ−R₃₄₂₁ⁿ+R₂₁₄₃ⁿ−R₄₃₁₂ⁿ)/4˜(R₁₂₃₄ⁿ−R₃₄₂₁ⁿ+R₂₁₄₃ⁿ−R₄₃₁₂ⁿ)   (18)

R _trans ⁿ =P ₂·(R₁₂₃₄ⁿ+R₃₄₂₁ⁿ+R₂₁₄₃ⁿ+R₄₃₁₂ⁿ)/4˜(R₁₂₃₄ⁿ+R₃₄₂₁ⁿ+R₂₁₄₃ⁿ+R₄₃₁₂ⁿ)   (19)

Thus, in the case of a harmonic progression or sinusoidal course of the input current signal, the individual distortion orders can be detected as separate frequency components by means of the Fourier analysis. All of these distortion orders can be based on different effects, which can be differentiated and separated from each other by such an analysis. A corresponding generalization is possible in the case where the input current signals consist of several harmonic alternating current signals with different fundamental frequencies.

The measuring device can be designed, for example, for Fourier-transforming the input current signals and/or the output voltage signals by means of discrete Fourier transformation (also referred to as DFT). Accordingly, the measuring device for detecting the input current signals and the output voltage signals may be made in the form of digital signals (eg by means of one or more analogue-to-digital converters and digital-to-analogue converters).

Hereinafter, some possible configurations and contact configurations of the power source, the switching device and the contact electrodes as well as some possible embodiments for detecting the input current signals will be described.

According to one embodiment, the switching device has at least one first, one second, one third and one fourth electrical input contact and at least one first, one second, one third and one fourth electrical output contact. According to this embodiment, the first input contact of the switching device is electrically connected to the first terminal of the power source, the second input contact of the switching device is electrically connected to the second terminal of the power source, the third input contact of the switching device is electrically connected to the first measuring input of the voltage measuring device, and the fourth input contact of the switching device is electrically connected to the second measuring input of the voltage measuring device. In addition, the first output contact of the switching device is electrically connected to the first connection contact, the second output contact of the switching device is electrically connected to the second connection contact, the third output contact of the switching device is electrically connected to the third connection contact, and the fourth output contact of the switching device is electrically connected to the fourth connection contact. When the measuring device is used as intended, the first output contact of the switching device is thus electrically connected to the first contact electrode, the second output contact of the switching device is electrically connected to the second contact electrode, the third output contact of the switching device is electrically connected to the third contact electrode, and the fourth output contact of the switching device is electrically connected to the fourth contact electrode. The switching device according to this embodiment is designed for the variable pairwise electrical connection of one each of the four input contacts with one each of the four output contacts. According to this embodiment, the switching means for variable pairwise connection of in each case one of the first terminals, the second terminals, the first measuring input and the second measuring input with one of the four connection contacts (or with one of the four contact electrodes) is formed in that the switching means for variable pairwise electrical connection of one of each of the four input contacts on the one hand to one of the four output contacts on the other hand. This makes an uncomplicated realization and integration of the switching device possible.

The power source may be a current source, eg, a DC power source or an AC power source. However, it can also be provided that the power source is a voltage source, for example a DC voltage source or an AC voltage source. If the power source is a DC power source or a DC power source, the input power is in the form of a DC current.

If the power source is an AC power source or an AC power source, the input power is in the form of an AC current.

In the embodiment of the power source as a voltage source it can be provided that one of the two terminals of the voltage source is connected to an electrical reference potential, for example, to the ground potential of the measuring device. In the embodiment of the voltage source as a DC voltage source, the measuring device may for example be designed such that one of the two terminals of the voltage source is connected to the ground potential, wherein the voltage source for supplying the other of the two terminals is formed with a DC potential or with a DC voltage. When designing the voltage source as an AC voltage source, the measuring device may be configured, for example, such that one of the two terminals of the voltage source is connected to the ground potential, wherein the voltage source for applying the other of the two terminals is formed with an AC potential or with an AC voltage.

In an embodiment of the voltage source as an alternating voltage source, it may alternatively be provided that the alternating voltage source is designed to act on the two terminals with mutually opposite-phase alternating voltages (where the voltage or potential difference between this terminal and the ground potential is always understood to be the voltage present at one pole). According to this embodiment, therefore, the alternating voltage applied to the first terminal is opposite in phase to the alternating voltage applied to the second terminal, so that the alternating voltage applied to the first terminal and the alternating voltage applied to the second terminal always have the same magnitude but different signs. Such symmetrical energization contributes to a high measuring accuracy.

The measuring device may comprise a current measuring device for detecting the electric current present between the first and the second terminal of the power source as an input current signal. It can be provided, for example, that the measuring device for detecting the input current signal has one or more electrical resistors (ie electrical components in the form of a resistor or resistance components) which are arranged in the current path of the input current. The measuring device can be designed, for example, for tapping or detecting the voltage drop across such a resistance component as a measuring voltage and determining the input current signal based on the detected measuring voltage—and, for example, the known electrical resistance of the resistance component (eg by forming the input current signal as the quotient of the measuring voltage and the resistance value). Such a resistance component is also referred to as a measuring resistor.

According to one embodiment, the measuring device accordingly has at least one resistance component which is connected in series with one of the two terminals of the power source between this terminal and the connection contacts (and thus also between these terminals and the contact electrodes). It can be provided, for example, that the resistance component is connected in series with one of the two terminals between this terminal and the switching device. Accordingly, the measuring device may, for example, comprise a resistance component which is connected in series with the first terminal of the power source between the first terminal and the connection contacts (and thus also between the first terminal and the contact electrodes), wherein the resistance component can be switched between the first terminal and the switching device. Alternatively or additionally, the measuring device may, for example, comprise a resistance component which is connected in series with the second terminal of the power source between the second terminal and the connection contacts (and thus also between the second terminal and the contact electrodes), wherein the resistance component, for example, can be switched between the second terminal and the switching device. It can be provided, for example, that the measuring device has a resistance component which is connected in series with the first terminal of the power source between the first terminal and the first input contact of the switching device. Alternatively or additionally, it can be provided that the measuring device has a resistance component which is connected in series with the second terminal of the power source between the second terminal and the second input contact of the switching device.

According to one embodiment, the measuring device has two resistance components with the same resistance value (eg two identically designed resistance components), the first of these two resistance components being connected in series with the first terminal of the power source between the first terminal and the connection contacts (eg between the first terminal and the switching device), and the second of these two resistance devices being connected in series with the second terminal of the power source between the second terminal and the connection contacts (eg, between the second terminal and the switching device). It can be provided, for example, that the measuring device has two resistance components with the same resistance value (eg two identically designed resistance components), wherein the first of these two resistance components is connected in series with the first terminal of the power source between the first terminal and the first input contact of the switching device and wherein the second of these two resistance devices is connected in series with the second terminal of the power source between the second terminal and the second input contact of the switching device. Such a configuration with two resistance components which have an equal resistance value (wherein the resistance value of the first resistance component is equal to the resistance value of the second resistance component) contributes to a high measurement accuracy due to the associated symmetry, in particular in combination with an AC voltage source which is designed to supply the two terminals with mutually opposite-phase AC voltages.

The measuring device can also be designed such that it can detect the voltage drop across this resistance component as a measuring voltage or measuring voltage signal for at least one of these connected in series with one terminal of the power source, and that based on the detected measuring voltage (and eg the known electrical resistance value of the resistance component), the input current signal can be determined.

The contact electrodes may be in different configurations. According to one embodiment, the measuring device is designed such that the contact electrodes can be moved relative to the measurement object (or to a measurement object receptacle of the measurement device). The measuring device may in particular be designed such that the contact points of the contact electrodes (provided for contacting the measurement object) are movable relative to the measurement object or to the measurement object receptacle. Accordingly, the measuring device can in particular have a measurement object receptacle provided for receiving or storing the measurement object, wherein the contact electrodes are movable relative to the measurement object receptacle. Because the first, second, third and fourth contact electrodes are movable relative to the measurement object or the measurement object receptacle, for example, different measurement objects can be characterized by means of the measuring device. In particular, the measurement object is not part of the measuring device. In addition, the contact electrodes are not permanently connected to the measurement object (in particular not materially bonded). In particular, the contact electrodes may be designed such that they can be moved relative to the measurement object or the measurement object receptacle such that after introducing a measurement object into the measurement object receptacle, the contact electrodes can be brought into contact with the measurement object, then the measurement for characterizing the measurement object can be performed, and after completion of the measurement, the contact electrodes can be brought out of contact with the measurement object, so that subsequently the measurement object can be removed from the measurement object receptacle.

According to one embodiment, the measuring device is also designed such that the contact electrodes are movable relative to one another and thus can be positioned variably relative to one another. The measuring device may in particular be designed such that the contact points of the contact electrodes (provided for contacting the measuring object) are movable relative to each other or can be variably positioned. Accordingly, the positions of the first, second, third and fourth contact electrodes relative to each other (and thus also the contact positions at which the contact electrodes contact the measurement object) can be variably adjusted, so that different contacting geometries are made possible. Accordingly, each of the contact electrodes may be disposed at different (eg, any) positions and brought into contact with the measurement object. In this regard, it can be provided, for example, that each of the contact electrodes is arranged at the free end of a flexible electrical conductor (eg a wire) or is formed by the same, so that the contact electrode or its contact point can be variably positioned by positioning the flexible electrical conductor.

According to another embodiment, the measuring device is designed such that the contact electrodes are not movable relative to each other, but are arranged relative to each other in a fixed predetermined geometry. It can be provided, for example, that the contact electrodes are arranged in a fixed predetermined geometry such that the connecting line between the first and the second contact electrode is not parallel and not perpendicular to the connecting line between the third and the fourth contact electrode. It can be provided in particular that the contact electrodes are arranged in a fixed predetermined geometry such that the connecting line between the contact point of the first contact electrode and the contact point of the second contact electrode is not parallel and not perpendicular to the connecting line between the contact point of the third contact electrode and the contact point of the fourth contact electrode. It can be provided, for example, that the four contact electrodes are arranged such that they (or their contact points) form the vertices of a rectangle (preferably an uneven rectangle, ie a rectangle in which the length is different than the width), wherein the first and second contact electrodes are diagonally opposite each other, and wherein the third and fourth contact electrodes are diagonally opposite each other. It can be provided, for example, that the measuring device has a contact element, wherein the contact electrodes (in particular the first, second, third and fourth contact electrodes) are fixed to the contact element while forming one of the above-explained geometries so that they are fixed relative to one another in a predetermined geometry. The contact element may be movable relative to the measurement object or relative to the measurement object receptacle. The specified geometries allow a reliable and accurate simultaneous determination of the longitudinal and transverse resistance.

The invention will now be described by way of example with reference to the accompanying figures, in which the same or similar features are given the same reference numerals; here are shown schematically:

FIG. 1 a measuring device according to an embodiment with an AC voltage source when characterizing a measurement object,

FIG. 2 an exemplary input current signal (FIG. 2A) and its Fourier transform (FIG. 2B), as well as an exemplary output voltage signal (FIG. 2C) and its Fourier transform (FIG. 2D), FIG.

FIG. 3 a contact member having contact electrode in a fixed geometry, and

FIG. 4 a measuring device according to an embodiment with a DC voltage source for characterizing a measuring object,

FIG. 1 shows a measuring device 1 according to one embodiment, characterizing the electrical resistance of a measuring object 3. The measuring object 3 is in the form of a material layer and is accommodated or stored in a measuring object receptacle 4 or measuring object holder 4 of the measuring device 1.

The measuring device 1 has an electrical power source 5 with a first terminal 7 and a second terminal 9. In the embodiment according to FIG. 1, the power source 5 is an electrical alternating voltage source 5, by means of which an electrical alternating voltage is provided, so that when there is an electrically conductive connection between the first 7 and the second 9 terminal from the alternating voltage source 5, an electric current is provided which is called the input current. Since, according to FIG. 1, the power source 5 is an alternating voltage source, the input current is an alternating current.

The measuring device 1 has a voltage measuring device 11 with a first measuring input 13 and a second measuring input 15. The voltage measuring device 11 is designed to detect the electrical voltage present between the first 13 and the second 15 measuring inputs, which is referred to as the output voltage. Since, according to FIG. 1, the input current is an alternating current, the output voltage is an alternating voltage.

The measuring device 1 also has a first contact electrode 17, a second contact electrode 19, a third contact electrode 21 and a fourth contact electrode 23. The contact electrodes are provided for physically and electrically contacting the measurement object 3. In the intended use of the measuring device 1—as shown in FIG. 1—the contact electrodes 17, 19, 21 and 23 are in physical contact with the measuring object 3, so that the measuring object 3 is electrically contacted by means of the contact electrodes.

The measuring device 1 has a switching device 27, which is connected between the power source 5 and the voltage measuring device 11 on the one hand and the contact electrodes 17, 19, 21, 23 on the other hand. The measuring device 1 has a first connection contact 16, a second connection contact 18, a third connection contact 20, and a fourth connection contact 22, wherein the connection contacts 16, 18, 20, 22 can be formed, for example, on the switching device 27. The connection contacts 16, 18, 20, 22 may be formed, for example, as connection sockets. The switching device 27 is designed for the variable pairwise electrical connection of in each case one of the first pole 7, the second pole 9, the first measuring input 13 and the second measuring input 15 on the one hand with one of the four connection contacts 16, 18, 20, 22 on the other hand. Each of the connection contacts is connected with one of the contact electrodes by means of a releasable electrical connection (eg a plug connection). The first connection contact 16 is electrically connected to the first contact electrode 17, the second connection contact 18 is electrically connected to the second contact electrode 19, the third connection contact 20 is electrically connected to the third contact electrode 21, and the fourth connection contact 22 is electrically connected to the fourth contact electrode 23. The measuring device 1 or the switching device 27 is thus designed for the variable pairwise electrical connection of in each case one of the first terminal 7, the second terminal 9, the first measuring input 13 and the second measuring input 15 on the one hand and with one of the four contact electrodes 17, 19, 21, 23rd on the other hand.

The switching device 27 has four electrical input contacts and four electrical output contacts, namely a first input contact 29, a second input contact 31, a third input contact 33, a fourth input contact 35, a first output contact 37, a second output contact 39, a third output contact 41 and a fourth output contact 43. The first input contact 29 is connected to the first terminal 7, the second input contact 31 is connected to the second terminal 9, the third input contact 33 is connected to the first measuring input 13, and the fourth input contact 35 is electrically connected to the second measuring input 15. The first output contact 37 is connected to the first connection contact 16 (and thus to the first contact electrode 17), the second output contact 39 is connected to the second connection contact 18 (and thus to the second contact electrode 19), the third output contact 41 is connected to the third connection contact 20 (and thus to the third contact electrode 21), and the fourth output contact 43 is electrically connected to the fourth connection contact 22 (and thus to the fourth contact electrode 23). The switching device 27 is designed for variable pairwise electrical connection of in each case one of the input contacts 29, 31, 33, 35 with one of the output contacts 37, 39, 41, 43 (illustrated in FIG. 1 by the intersecting dashed lines, which illustrate the operation of the switching device 27 as a switching matrix).

The measuring device 1 is designed in such a way that from it the electrical current which, when the first terminal 7 is electrically connected to the ith connection contact or the ith contact electrode and the second terminal 9 is electrically connected to the jth connection contact or the jth contact electrode between the first terminal 7 and the second terminal 9, is detected as an input current signal I ij (where i, j=1, 2, 3, 4 and i≠j). For this purpose, the measuring device 1 has an electrical resistance component 45, which also functions as and is designated as a measuring resistor 45. The measuring resistor 45 is connected in series with the first terminal 7 between the first terminal 7 and the connection contacts 16, 18, 20, 22 (and thus also between the first terminal 7 and the contact electrodes 17, 19, 21, 23), in particular between the first terminal 7 and the switching device 27. In the present case, the measuring resistor 45 is connected as an example between the first terminal 7 of the power source 5 and the first input contact 29 of the switching device 27.

The measuring device 1 is designed to detect the voltage drop across the measuring resistor 45 as a measuring voltage and to determine the input current signal l_ij based on the detected measuring voltage. The measuring device 1 has, as an example, a current signal generating device 47 which is designed to pick up or detect the electrical voltage drop across the measuring resistor 45 and determine the electrical current corresponding to this voltage as the input current l_ij (eg by forming the input current signal as the quotient of the measuring voltage and the known resistance of the measuring resistor 45). The input current signal l_ij describes the input current as a function of time and is therefore also expressed as l_ij=l_ij(t) written, where t denotes the time.

According to the embodiment of FIG. 1, the measuring device 1 also has a second electrical resistance component 49 which is connected in series with the second terminal 9 between the second terminal 9 and the connection contacts 16, 18, 20, 22 (and thus also between the second terminal 7 and the contact electrodes 17, 19, 21, 23), in particular between the second terminal 9 and the switching device 27. In the present case, as an example, the second resistance component 49 is connected between the second terminal 9 of the power source 5 and the second input contact 31 of the switching device 27. The resistance of the second resistance device 49 is the same as the resistance of the first resistance device 45, for example, the first resistance device 45 and the second resistance device 49 are made to be identical to each other. The second resistance component 49 can also act as a measuring resistor for detecting the input current signal, wherein the measuring device 1 for detecting the voltage drop across the second resistance component 49 can be designed as a measuring voltage and determining the input current signal l_ij based on the detected measuring voltage (not shown in FIG. 1). However, provision may also be made for the second resistance component 49 to be introduced in addition to the measuring resistor 45 for reasons of symmetry alone.

Due to the electrical input current l_ij between the i-th and the j-th contact electrode, an electrical voltage is induced between the two remaining contact electrodes, ie between the k-th and the l-th contact electrode (where k, l=1, 2, 3, 4 and k≠l). One of these two remaining contact electrodes is electrically connected to the first measuring input 13 of the voltage measuring device 11, and the other of these two remaining contact electrodes is electrically connected to the second measuring input 15. The measuring device 1 is designed such that it measures the electrical voltage which is present upon electrical connection of the first measuring input 13 with the kth contact electrode and electrical connection of the second measuring input 15 with the lth contact electrode between the first measuring input 13 and the second measuring input 15, as an output voltage signal U_kl. The output voltage signal U_kl describes the output voltage as a function of time and is therefore also written as U_kl=U_kl(t), where t denotes the time.

The measuring device 1 is designed by means of the switching device 27 for carrying out a first, second, third and fourth measuring sequence as follows.

In the first measurement sequence:

• • the first connection contact 16 (and thus also the first contact electrode 17) is electrically connected to the first terminal 7, in that the first input contact 29 is electrically connected to the first output contact 37 by the switching device 27,
  • the second connection contact 18 (and therefore also the second contact electrode 19) is electrically connected to the second terminal 9, in that the second input contact 31 is electrically connected to the second output contact 39 by the switching device 27,
  • the third connection contact 20 (and thus also the third contact electrode 21) is electrically connected to the first measuring input 13, while the third input contact 33 is electrically connected to the third output contact 41 of the switching device 27, and
  • the fourth connection contact 22 (and thus also the fourth contact electrode 23) is electrically connected to the second measurement input 15, in that the fourth input contact 35 is electrically connected to the fourth output contact 43 by the switching device 27,
  • wherein the input current present between the first 16 and the second 18 connection contact (or between the first 17 and the second 19 contact electrode) is detected as a first input current signal l₁₂, and wherein the voltage present between the third 20 and the fourth 22 connection contact (or between the third 21 and the fourth 23 contact electrode) is detected as the first output voltage signal U₃₄.

In the second measurement sequence:

• • the third connection contact 20 (and thus also the third contact electrode 21) is electrically connected to the first terminal 7, in that the first input contact 29 is electrically connected to the third output contact 41 by the switching device 27,
  • the fourth connection contact 22 (and thus also the fourth contact electrode 23) is electrically connected to the second terminal 9, in that the second input contact 31 is electrically connected to the fourth output contact 43 by the switching device 27,
  • the second connection contact 18 (and thus also the second contact electrode 19) is electrically connected to the first measuring input 13 in that the third input contact 33 is electrically connected to the second output contact 39 by the switching device 27, and
  • the first connection contact 16 (and therefore also the first contact electrode 17) is electrically connected to the second measurement input 15, in that the fourth input contact 35 is electrically connected to the first output contact 37 by the switching device 27,
  • wherein the input current present between the third 20 and the fourth 22 connection contact (or between the third 21 and the fourth 23 contact electrode) is detected as a second input current signal l₃₄, and wherein the voltage present between the first 16 and the second 18 connection contact (or between the first 17 and the second 19 contact electrode) is detected as the second output voltage signal U₂₁.

In the third measurement sequence:

• • the second connection contact 18 (and therefore also the second contact electrode 19) is electrically connected to the first terminal 7, in that the first input contact 29 is electrically connected to the second output contact 39 by the switching device 27,
  • the first connection contact 16 (and thus also the first contact electrode 17) is electrically connected to the second pole 9, in that the second input contact 31 is electrically connected to the first output contact 37 by the switching device 27,
  • the fourth connection contact 22 (and thus also the fourth contact electrode 23) is electrically connected to the first measuring input 13 in that the third input contact 33 is electrically connected to the fourth output contact 43 by the switching device 27, and
  • the third connection contact 20 (and therefore also the third contact electrode 21) is electrically connected to the second measurement input 15 in that the fourth input contact 35 is electrically connected to the third output contact 41 by the switching device 27,
  • wherein the input current present between the second 18 and the first 16 connection contacts (or between the second 19 and first 17 contact electrode) is detected as a third input current signal l₂₁, and wherein the voltage present between the fourth 22 and the third 20 connection contact (or between the fourth 23 and the third 21 contact electrode) is detected as a third output voltage signal U₄₃.

In the fourth measurement sequence:

• • the fourth connection contact 22 (and thus also the fourth contact electrode 23) is electrically connected to the first terminal 7, in that the first input contact 29 is electrically connected to the fourth output contact 43 by the switching device 27,
  • the third connection contact 20 (and therefore also the third contact electrode 21) is electrically connected to the second pole 9, in that the second input contact 31 is electrically connected to the third output contact 41 by the switching device 27,
  • the first connection contact 16 (and thus also the first contact electrode 17) is electrically connected to the first measuring input 13, in that the third input contact 33 is electrically connected to the first output contact 37 by the switching device 27, and
  • the second connection contact 18 (and therefore also the second contact electrode 19) is electrically connected to the second measuring input 15, in that the fourth input contact 35 is electrically connected to the second output contact 39 by the switching device 27,
  • wherein the input current present between the fourth 22 and the third 20 connection contact (or between the fourth 23 and the third 21 contact electrode) is detected as a fourth input current signal l₄₃, and wherein the voltage present between the first 16 and the second 18 connection contact (or between the first 17 and second 19 contact electrode) is detected as the fourth output voltage signal U₁₂.

In the embodiment according to FIG. 1, the power source 5 is designed to provide an alternating voltage, the alternating voltage source 5 being designed as an example for providing a harmonic or sinusoidal alternating voltage. As an example, the AC voltage source 5 is designed such that the first terminal 7 and the second terminal 9 are acted upon with antiphase AC voltages or AC potentials, so that for the AC voltage applied to the first terminal 7 U 1 (t) and the AC voltage applied at the second terminal 9 U 2 (t, U 1 (t)=−U 2 (t) applies (as illustrated in FIG. 1 by the sinusoids phase-shifted by 180°). Alternatively, the AC voltage source 5 may be made (not shown) such that one of the two terminals (eg, the first terminal 7) is connected to the ground potential of the measuring device 1, and that to the other of the two terminals (eg, the second terminal 9) an alternating voltage potential or an alternating voltage is applied (not shown).

The measuring device 1 is formed by means of the evaluation device 51 for determining the longitudinal resistance R_long and the transverse resistance R_trans of the measuring object 3 based on the first, second, third and fourth input current signals and based on the first, second, third and fourth output voltage signals, as explained in more detail below.

According to the embodiment of FIG. 1, the measuring device 1 is designed to Fourier-transform the first, second, third and fourth input current signals l_ij(t) and to Fourier-transform the first, second, third and fourth output voltage signals U_kl(t). In addition, the measuring device 1 is designed to determine the longitudinal resistance R_long and the transverse resistance R_trans of the measuring object 3 based on the Fourier-transformed input current signals and the Fourier-transformed output voltage signals. In the present case, for example, the input current signals l_ij(t) and the output voltage signals U_kl(t) are detected as analogue signals, these analogue signals are digitized and thus converted into digital signals, and these digital signals are Fourier-transformed by means of discrete Fourier transformation (also referred to as DFT). This can be realized, for example, by the measuring device 1 having a first analogue-to-digital converter ADC1 for converting the input current signals l_ij(t) into digital signals and a first Fourier analyser DFT1 for Fourier-transforming the digitized input current signals by means of DFT, and by the measuring device 1 having a second analogue-to-digital converter ADC2 for converting the output voltage signals U_kl(t) into digital signals and a second Fourier analyser DFT2 for Fourier-transforming the digitized output voltage signals by means of DFT. It can also be provided that the analogue-to-digital converters ADC1 and ADC2 as well as the Fourier analysers DFT1 and DFT2 (or their functionality) are implemented in the evaluation device 51.

The harmonic alternating voltage provided by the power source 5 leads to harmonic or sinusoidal input current signals l_ij(t) according to equation (11), ie the first input current signal l₁₂, the second input current signal l₃₄, the third input current signal l₂₁ and the fourth input current signal l₄₃ can be written in a form according to equation (11).

FIG. 2A shows the time profile of an exemplary harmonic input current signal l_ij(t) of the form

l _ij(t)=A_ij sin(ω₁ t)

according to equation (11). FIG. 2B shows the associated Fourier-transformed input current signal l_ij(ω), which is in the form of a frequency domain signal. FIG. 2C shows the time profile of an exemplary output voltage signal l_ij(t) produced by the input current signal U_kl(t), FIG. 2D showing the associated Fourier transform output voltage signal U_kl(ω), which is in the form of a frequency domain signal and according to equation (12) can be written as a weighted sum of several harmonic orders n. In the present example, n=1, 2, 3, so that the output voltage signal can be written as

U _kl(t)=B_kl¹·sin(ω₁·t)+B_kl²·sin(2·ω₁·t)+B_kl³·sin(3·ω₁·t),

where for the sake of simplicity it has been assumed that the phases φ_klⁿ are zero.

The harmonic-dependent resistance elements R_ijklⁿ result from the equations (13) to (15), where in the present case due to the vanishing initial phases φ_klⁿ the imaginary part of the harmonic-dependent resistance elements R_ijklⁿ disappears and the resistance elements R_ijklⁿ for n=1, 2, 3 are thus given by R_ijkl¹=B_kl¹/A_ij, R_ijkl²=B_kl²/A_ij and R_ijkl³=B_kl³/A_ij. From these harmonic-dependent resistance elements R_ijklⁿ in turn, according to equations (16) and (17) or according to equations (18) and (19), the longitudinal resistance R_longⁿ and the transverse resistance R_transⁿ can be determined for different harmonic orders n. Accordingly, in the embodiment according to FIG. 1, the evaluation device 51 is designed as an example for evaluating the detected Fourier transform input current signals and the Fourier transform output voltage signals according to equations (11) to (15), the longitudinal resistance and the transverse resistance being determined either according to equations (16) and (17) or according to equations (18) and (19). Since equations (11) to (19) correspond to equations (2) to (10) for n=1, the embodiment according to FIG. 1 is designed in particular for evaluating the detected signals in accordance with equations (2) to (10). The measuring device 1 is also designed (eg by means of the evaluation device 51 or a data memory implemented therein) for storing the detected input current signals, the detected output voltage signals, and the determined resistance values.

The measuring device 1 has a measurement object receptacle 4 for storing the measurement object 3. Each of the contact electrodes 17, 19, 21, 23 is formed with a tip, the tip functioning as a contact point for contacting the measurement object 3. The measuring device 1 is designed such that the first 17, second 19, third 21 and fourth 23 contact electrodes (or their contact points) are movable relative to the measurement object receptacle 4 and the measurement object 3 (illustrated in FIG. 1 by the double arrow 53). In the embodiment of FIG. 1, the measuring device 1 has a contact element 55, wherein the contact electrodes 17, 19, 21, 23 are fixed in a fixed predetermined geometry on the contact element 55. The contact element 55 can be moved together with the contact electrodes along the direction of movement indicated by the double arrow 55 relative to the measurement object receptacle 4. In the embodiment of FIG. 1, the contact electrodes are fixed in such a geometry on the contact member 55 that the connecting line between the first 17 and the second 19 contact electrode is not parallel and not perpendicular to the connecting line between the third 21 and the fourth 23 contact electrode. In the present case, the contact electrodes are arranged as an example such that the contact electrodes (or their contact points) form the vertices of a scalene rectangle, with the first 17 and second 19 contact electrodes facing each other diagonally, and with the third 21 and fourth 23 contact electrodes facing each other diagonally. FIG. 3 illustrates the contact element 55 with the contact electrodes 17, 19, 21 and 23, which are in the form of a scalene rectangle.

FIG. 4 shows a measuring device 1 according to a further embodiment. In contrast to the embodiment according to FIG. 1, in the embodiment according to FIG. 4 the power source 5 is designed as a DC voltage source 5, from which a direct electrical voltage is provided between the terminals 7 and 9. Thus, in the embodiment of FIG. 4, the input current is a direct current. The measuring device according to FIG. 4 is designed for carrying out the first, second, third and fourth measuring sequences with the corresponding wiring configurations already described with reference to FIG. 1, in particular for detecting the associated first, second, third and fourth input current signals l_ij(t) and for detecting the first, second, third and fourth output voltage signals U_kl(t).

Since the measuring device 1 according to FIG. 4 is operated with a DC voltage, evaluation of the detected input current signals and output voltage signals without Fourier transformation can take place here. In contrast to the embodiment according to FIG. 1, in particular the analogue-to-digital converters ADC1 and ADC2 as well as the Fourier analysers DFT1 and DFT2 can be dispensed with in the measuring device 1 according to FIG. 4. In addition, the measuring device 1 according to FIG. 4 is designed without the second resistance component 49.

The measuring device 1 according to FIG. 4 is designed as an example in such a way that with this in the respective measurement sequence using the current signal generating device 47, the first input current signal I 12, the second input current signal I 34, the third input current signal I 21, the fourth input current signal I 43 and by means of voltage measuring device 11, the first output voltage signal U 34, the second output voltage signal U 21, the third output voltage signal U 43 and the fourth output voltage signal U 12 are detected. Since according to FIG. 4 the input current is a DC current, the output voltage is a DC voltage.

The measuring device 1 according to FIG. 4 is designed to determine the longitudinal resistance R_long and the transverse resistance R_trans of the measuring object 3 based on the first, second, third and fourth input current signals and based on the first, second, third and fourth output voltage signals, as explained in more detail below.

According to the embodiment of FIG. 4, the measuring device 1 according to R ijkl=U kl/I ij according to equation (1) for determining the quotient U 34/I 12 from the first output voltage signal U 34 and the first input current signal I 12 as the first resistance value R 1234 for determining the quotient U 21/I 34 from the second output voltage signal U 21 and the second input current signal I 34 as the second resistance R 3421, for determining the quotient U 43/I 21 from the third output voltage signal U 43 and the third input current signal I 21 third resistance value R 2143, and for determining the quotient U 12/I 43 of the fourth output voltage signal U 12 and the fourth input current signal I 43 as a fourth resistance R 4312 are formed.

From these resistance elements R_ijkl, the longitudinal resistance R_long and the transverse resistance R_trans can in turn be determined according to equations (7) and (8) or according to equations (9) and (10). Accordingly, in the embodiment of FIG. 4, the evaluation device 51 is formed as an example for evaluating the detected input current signals and output voltage signals according to equations (1) and (7) to (10), wherein the longitudinal resistance and the transverse resistance are determined either according to equations (7) and (8) or according to equations (9) and (10).

In contrast to the measuring device according to FIG. 1, in the measuring device according to FIG. 4 the contact electrodes 17, 19, 21, 23 are not fixed by means of a contact element, but are movable relative to one another (whereby also according to FIG. 4 the contact electrodes are movable relative to the measuring object receptacle 4 and the measuring object 3).

Otherwise, the embodiment of the measuring device 1 according to FIG. 4 is identical to that according to FIG. 1, so that in this regard reference is made to the explanations made for the embodiment according to FIG. 1.

LIST OF REFERENCE NUMBERS USED

• 1 Measuring device
• 3 Measurement object
• 4 Measuring object receptacle/measuring object holder
• 5 Electrical power source
• 7 First terminal of the power source
• 9 Second terminal of the power source
• 11 Voltage measuring device
• 13 First measuring input of the voltage measuring device
• 15 Second measuring input of the voltage measuring device
• 16 First connection contact
• 17 First contact electrode
• 18 Second connection contact
• 19 Second contact electrode
• 20 Third connection contact
• 21 Third contact electrode
• 22 Fourth connection contact
• 23 Fourth contact electrode
• 27 Switching device
• 29 First input contact of the switching device
• 31 Second input contact of the switching device
• 33 Third input contact of the switching device
• 35 Fourth input contact of the switching device
• 37 First output contact of the switching device
• 39 Second output contact of the switching device
• 41 Third output contact of the switching device
• 43 Fourth output contact of the switching device
• 45 First electrical resistance component/measuring resistor
• 47 Current signal generator
• 49 Second electrical resistance component/measuring resistor
• 51 Evaluation device
• 53 Freedom of movement of the contact electrodes/the contact element
• 55 Contact element with contact electrodes fixed thereto
• I₁₂ First input current signal
• I₃₄ Second input current signal
• I₂₁ Third input current signal
• I₄₃ Fourth input current signal
• U₃₄ First output voltage signal
• U₂₁ Second output voltage signal
• U₄₃ Third output voltage signal
• U₁₂ Fourth output voltage signal
• U₁, U₂ Antiphase AC voltages/AC potentials
• R₁₂₃₄ First resistance element
• R₃₄₂₁ Second resistance element
• R₂₁₄₃ Third resistance element
• R₄₃₁₂ Fourth resistance element
• R_ijklⁿ Resistance element for harmonic order n
• R_trans Transverse resistance/cross resistance
• R_long Longitudinal resistance/Series resistance
• R_longⁿ Longitudinal resistance to harmonic order n
• R_transⁿ Transverse resistance to harmonic order n
• ADC1 First analogue-to-digital converter
• ADC2 Second analogue-to-digital converter
• DFT1 First Fourier analyser
• DFT2 Second Fourier analyser

Claims

1. A measuring device for characterising an electrical resistance of a measurement object, the measuring device comprising: an electric power source having a first terminal and a second terminal for providing an electric current as an input current,a voltage measuring apparatus having a first measuring input and a second measuring input for detecting an electrical voltage as an output voltage,at least one first connection contact for connecting a first contact electrode, a second connection contact for connecting a second contact electrode, a third connection contact for connecting a third contact electrode, and a fourth connection contact for connecting a fourth contact electrode, wherein the first, second, third and fourth contact electrodes are provided for electrically contacting the measurement object,a switching apparatus designed for a variable pairwise electrical connection of in each case one of the first terminal, the second terminal, the first measuring input and the second measuring input, on the one hand, to one of the four connection contacts, on the other hand, such thatthe measuring device is designed to perform at least a first and a second measuring sequence, whereinin the first measuring sequence, by means of the switching apparatus the first connection contact is electrically connected to one of the first and second terminals, the second connection contact is electrically connected to the other of the first and second terminals, the third connection contact is electrically connected to one of the first and the second measuring inputs, and the fourth connection contact is electrically connected to the other of the first and the second measuring inputs, wherein the input current present between the first and second connection contacts is detected as a first input current signal, and wherein the voltage present between the third and the fourth connection contacts is detected as the first output voltage signal,in the second measuring sequence, by means of the switching apparatus the third connection contact is electrically connected to one of the first and the second terminals, the fourth connection contact is electrically connected to the other of the first and the second terminals, the first connection contact is electrically connected to one of the first and the second measuring inputs, and the second connection contact is electrically connected to the other of the first and the second measuring inputs, wherein the input current present between the third and the fourth connection contacts acts as a second input current signal, and wherein the voltage present between the first and second connection contacts is detected as the second output voltage signal, andwherein the measuring device is designed for determining the series resistance of the measurement object by incorporating the first and the second input current signals and the first and the second output voltage signals.

2. The measuring device according to claim 1, wherein the measuring device is designed for determining a cross resistance of the measuring object by incorporating the first and the second input current signals and the first and the second output voltage signals.

3. The measuring device according to claim 1, wherein, in addition to the first and second measuring sequence, the measuring device is designed for performing at least one third and fourth measuring sequence such that in the first measuring sequence, by means of the switching apparatus the first connection contact is electrically connected to the first terminal, the second connection contact is electrically connected to the second terminal, the third connection contact is electrically connected to the first measuring input, and the fourth connection contact is electrically connected to the second measuring input, wherein the input current present between the first and the second connection contacts is detected as the first input current signal, and wherein the voltage present between the third and the fourth connection contacts is detected as the first output voltage signal,in the second measuring sequence, by means of the switching apparatus the third connection contact is electrically connected to the first terminal, the fourth connection contact is electrically connected to the second terminal, the second connection contact is electrically connected to the first measurement input, and the first connection contact is electrically connected to the second measuring input, wherein the input current present between the third and the fourth connection contacts is detected as the second input current signal, and wherein the voltage present between the second and the first connection contacts is detected as the second output voltage signal,in the third measuring sequence, by means of the switching apparatus the second connection contact is electrically connected to the first terminal, the first connection contact is electrically connected to the second terminal, the fourth connection contact is electrically connected to the first measuring input, and the third connection contact is electrically connected to the second measuring input, wherein the input current present between the second and the first connection contacts is detected as the third input current signal, and wherein the voltage present between the fourth and the third connection contacts is detected as the third output voltage signal,in the fourth measuring sequence, by means of the switching apparatus the fourth connection contact is electrically connected to the first terminal, the third connection contact is electrically connected to the second terminal, the first connection contact is electrically connected to the first measurement input, and the second connection contact is electrically connected to the second measuring input, wherein the input current present between the fourth and third terminal contacts is detected as the fourth input current signal, and the voltage present between the first and second connection contacts present is detected as the fourth output voltage signal, andwherein the measuring device is designed for determining the series resistance and/or the cross resistance of the measuring object by incorporating the first, second, third and fourth input current signals and the first, second, third and fourth output voltage signals.

4. The measuring device according to claim 1, wherein the measuring device is designed for determining a first resistance value from the first output voltage signal and the first input current signal, for determining a second resistance value from the second output voltage signal and the second input current signal, and for determining the series resistance and/or the cross resistance of the measurement object on the basis of on the first and the second resistance value.

5. The measuring device according to claim 3, wherein the measuring device is designed for determining a first resistance value from the first output voltage signal and the first input current signal, for determining a second resistance value from the second output voltage signal and the second input current signal, for determining a third resistance value from the third output voltage signal and the third input current signal, for determining a fourth resistance value from the fourth output voltage signal and the fourth input current signal, and for determining the series resistance and/or the cross resistance of the measuring object on the basis of the first, second, third and fourth resistance values.

6. The measuring device according to claim 1, wherein the measuring device has a first contact electrode, a second contact electrode, a third contact electrode and a fourth contact electrode for electrically contacting the measurement object, wherein the first contact electrode is connected to the first connection contact, the second contact electrode is connected to the second connection contact, the third contact electrode is connected to the third connection contact and the fourth contact electrode is connected to the fourth connection contact.

7. The measuring device according to claim 1, wherein the input current is an alternating current.

8. The measuring device according to claim 1, wherein the measuring device is designed for a Fourier transformation of the input current signals and/or output voltage signals detected by the measuring device.

9. The measuring device according to claim 8, wherein the measuring device is designed for characterising the series resistance and/or the cross resistance of the measuring object on the basis of the Fourier-transformed input current signals and/or the Fourier-transformed output voltage signals.

10. The measuring device according to claim 1, wherein the switching apparatus has at least a first, a second, a third and a fourth electrical input contact and at least a first, a second, a third and a fourth electrical output contact,wherein the first input contact is electrically connected to the first terminal, the second input contact is electrically connected to the second terminal, the third input contact is electrically connected to the first measuring input, and the fourth input contact is electrically connected to the second measuring input,wherein the first output contact is electrically connected to the first connection contact, the second output contact is electrically connected to the second connection contact, the third output contact is electrically connected to the third connection contact, and the fourth output contact is electrically connected to the fourth connection contact, andwherein the switching apparatus is designed for the variable pairwise electrical connection of in each case one of the input contacts to one of the output contacts.

11. The measuring device according to claim 1, wherein the electrical power source is an AC voltage source, and wherein the AC voltage source is designed for supplying AC voltages in phase opposition to the first and the second terminals.

12. The measuring device according to claim 1, wherein the measuring device has at least one resistance component connected in series with one of the two terminals of the power source between this terminal and the connection contacts.

13. The measuring device according to claim 12, wherein the measuring device has two resistance components of equal resistance, wherein a first of the two resistance components is connected in series with the first terminal of the power source between the first terminal and the connection contacts, and wherein a second of the two resistance components is connected in series with the second terminal of the power source between the second terminal and the connection contacts.

14. The measuring device according to claim 12, wherein the measuring device is designed for detecting the voltage dropping across at least one of the resistance components as a measuring voltage and for determining the input current signals on the basis of the detected measuring voltage.