DEVICE AND METHOD FOR DETERMINING A TEMPERATURE-DEPENDENT IMPEDANCE CURVE ALONG AN ELECTRICAL CONDUCTOR

Abstract

The invention relates to a device for determining a temperature-dependent impedance curve along an electrical conductor, which device has a signal generator unit, which is arranged and designed to generate a multi-frequency electrical signal, which passes through an electrical conductor. The device also has a frequency spectrum sensing unit, which is arranged and designed to sense a frequency spectrum of a multi-frequency electrical signal leaving the conductor at least in a predefined frequency range. The device also has a frequency spectrum difference determination unit, which is arranged and designed to determine a frequency difference between the sensed frequency spectrum and a predefined frequency spectrum. The device also has a frequency difference conversion unit, which is designed and arranged to determine an amplitude curve of the determined frequency difference along the electrical conductor.

Claims

1. A device for determining a temperature-dependent impedance curve along an electrical conductor, having: a signal generator unit, which is arranged and designed to generate a multi-frequency electrical signal with constant power, which passes through an electrical conductor, a frequency spectrum sensing unit, which is arranged and designed to sense a frequency spectrum of a multi-frequency electrical signal leaving the conductor at least in a predefined frequency range, wherein the signal generator unit and the frequency spectrum sensing unit are jointly formed by a software-defined radio (SDR), a frequency spectrum difference determination unit, which is arranged and designed to determine a frequency difference between the sensed frequency spectrum and a predefined frequency spectrum, and a frequency difference conversion unit, which is arranged and designed to determine an amplitude representation in the time domain of the determined frequency difference along the electrical conductor.

2. Device according to claim 1, wherein the multi-frequency electrical signal is a noise signal, in particular a continuous white noise signal, or the multi-frequency electrical signal is a time-variant signal, in particular a frequency sweep.

3. Device according to claim 1, further having an amplifier unit, which is arranged and designed to amplify the multi-frequency electrical signal.

4. Device according to claim 1, further having a directional coupler, which is connected electrically conductively to a conductor end of the electrical conductor and is arranged and designed to introduce the multi-frequency electrical signal generated by the signal generator unit into the electrical conductor, and to lead out a multi-frequency electrical signal reflected by the electrical conductor as the multi-frequency electrical signal leaving the electrical conductor, wherein the electrical conductor has in particular one open conductor end, which reflects at least a portion of the signal introduced into the electrical conductor.

5. Device according to claim 1, wherein the frequency spectrum sensing unit is arranged and designed to determine at least a phase information of the multi-frequency electrical signal leaving the conductor, and/or the frequency spectrum sensing unit has a frequency sensing range from 25 to 1750 MHz, and/or the frequency spectrum sensing unit has software-based signal processing, and/or the frequency spectrum sensing unit has a USB port.

6. Device according to claim 1, wherein the predefined frequency spectrum is a frequency spectrum, sensed by the frequency spectrum sensing unit, of the electrical signal leaving the electrical conductor or an electrical reference conductor under predefined conditions, wherein the predefined conditions comprise in particular a freedom from damage and/or a constant temperature, preferably of 20 degrees Celsius, of the electrical conductor or the reference conductor.

7. Device according to claim 1, wherein the frequency difference conversion unit is arranged and designed to determine the amplitude curve along the electrical conductor using an inverse Fourier transform, in particular a fast inverse Fourier transform, of the frequency difference, and/or the frequency difference conversion unit is further arranged and designed to use phase information for a propagation time or conductor length referencing of the amplitude curve.

8. Device according to claim 1, wherein the electrical conductor is enclosed by a dielectric with temperature-variant properties, in particular by a dielectric with a temperature-dependent dielectric constant.

9. Method for determining a temperature-dependent impedance curve along an electrical conductor with the steps: generation of a multi-frequency electrical signal with constant output, which passes through an electrical conductor, with a software-defined radio (SDR), sensing of a frequency spectrum, at least in a predefined frequency range, of a multi-frequency electrical signal leaving the conductor with the SDR, determination of a frequency difference between the sensed frequency spectrum and a predefined frequency spectrum, and determination of an amplitude representation in the time domain of the frequency difference along the electrical conductor.

10. Method according to claim 9, further comprising at least one of the steps: amplification of the multi-frequency electrical signal introduction of the multi-frequency electrical signal into the electrical conductor, leading out of a multi-frequency electrical signal reflected by the electrical conductor as the multi-frequency signal leaving the conductor, wherein the electrical conductor has in particular an open conductor end, which reflects at least a portion of the multi-frequency signal introduced into the electrical conductor.

Description

DETAILED DESCRIPTION

[0049] FIG. 1 shows schematically the construction of a measuring arrangement for time domain reflectrometry.

[0050] In the variant A shown in FIG. 1, a (pulse) signal is supplied via a directional coupler to a cable. The cable is connected electrically conductively to the directional coupler only at one end, while an opposite cable end is open or electrically isolated.

[0051] A (pulse) signal reflected by the cable end is led out by the directional coupler and supplied to an evaluation or representation means, for example with an oscilloscope. The cable length can be deduced by determining the propagation time of the signal.

[0052] If the cable is cut at one point, the (pulse) signal is reflected at this point. A position of the separation point can be determined by a propagation time measurement of the reflected signal.

[0053] If the cable is not cut, but is damaged at a point, so that an impedance of the line is increased at a point or in a locally delimited area, the increased impedance causes a partial reflection of the (pulse) signal. By means of the propagation time measurement of the partially reflected (pulse) signal there can be determined a position of the increased impedance, and by means of the amplitude of the partially reflected (pulse) signal, a relation of the increased impedance to the line impedance surrounding the damage.

[0054] In contrast to variant A, in the variant B shown in FIG. 1 the (pulse) signal is conducted completely through a cable electrically contacted at two cable ends. The signal which leaves the cable is subtracted from the signal which is supplied to the cable and the difference signal determined in this way is evaluated or represented analogously to variant A.

[0055] FIG. 2 shows schematically the construction of a measuring arrangement for frequency domain reflectrometry or vector frequency domain reflectrometry.

[0056] In the variant A shown in FIG. 2, a multi-frequency signal is supplied to a cable via a directional coupler. The cable is connected electrically conductively to the directional coupler only at one end, while an opposite cable end is open or electrically isolated.

[0057] The frequency spectrum of the reflected multi-frequency signal is sensed and led out by the directional coupler.

[0058] A transformation of the sensed frequency spectrum into an amplitude representation/time domain representation, for example with an oscilloscope, shows the curve of a voltage drop/an impedance along the cable.

[0059] In the variant B shown in FIG. 2, the multi-frequency signal, in contrast to variant A of FIG. 2 and by analogy with variant B in FIG. 1, is conducted completely through a cable electrically contacted at two cable ends. The frequency spectrum of the signal leaving the cable is subtracted from the frequency spectrum of the signal supplied to the cable and the difference spectrum determined thus is evaluated or represented analogously to variant A.

[0060] FIG. 3 shows by way of example and schematically an embodiment of a device for determining a temperature-dependent impedance curve along an electrical cable.

[0061] A multi-frequency generator 10 produces a multi-frequency signal. The multi-frequency signal is amplified by an amplifier 20 and then supplied to a directional coupler 30. In the exemplary embodiment shown in FIG. 3, the multi-frequency signal is a time-invariant noise signal, but embodiments with a time-variant multi-frequency signal, for example with a frequency sweep, are also possible.

[0062] The directional coupler 30 conducts the amplified multi-frequency signal to a cable 40, wherein one end of the cable 40 is connected electrically conductively to the directional coupler 30 and another cable end is open or electrically isolated.

[0063] The amplified multi-frequency signal is reflected by the cable 40, in particular by the open or isolated cable end. The reflected amplified multi-frequency signal is supplied by the directional coupler 30 to a software-defined radio, SDR for short, 50. The SDR 50 determines a frequency spectrum of the reflected amplified multi-frequency signal.

[0064] In a further development (not shown) the multi-frequency signal is generated by the SDR 50 and supplied to the amplifier 20. The SDR thus replaces the multi-frequency generator 10 in this further development, wherein this is not in conflict with the function of the SDR 50 in the device shown in FIG. 3. The SDR 50 thus makes it possible to save on device constituents in this further development. A (construction) size of the device shown can thus be reduced and the costs of implementing the device shown can be reduced by this.

[0065] In embodiments of the device (not shown) which provide a multi-frequency signal in the form of a frequency sweep, for example, the SDR 50 can also determine phase information of the reflected amplified multi-frequency signal.

[0066] The frequency spectrum of the reflected amplified multi-frequency signal determined by the SDR 50 is further supplied to a frequency spectrum difference determination unit 70. The frequency spectrum difference determination unit 70 determines a frequency difference between the frequency spectrum of the reflected amplified multi-frequency signal and a reference spectrum 60.

[0067] The reference spectrum 60 has been defined previously by a determination of a reflected amplified multi-frequency signal of a reference cable (not shown). To this end a signal identical to the amplified multi-frequency signal, preferably a signal generated by the same arrangement of multi-frequency generator 10, amplifier 20 and directional coupler 30, is supplied to the reference cable and by analogy with the arrangement shown in FIG. 3 a frequency spectrum/reference spectrum is determined. The reference cable is a cable identical or at least identical in properties to the cable 40 that is free of damage and has a uniform/constant temperature of 20 C. By analogy with the arrangement shown in FIG. 3, one cable end of the reference cable is open or electrically isolated during determination of the reflected electrical multi-frequency signal.

[0068] In other words, in the device shown in FIG. 3, the frequency spectrum actually determined by the SDR 50 of the reflected amplified multi-frequency signal is compared with a predefined target spectrum.

[0069] The frequency difference determined by the frequency spectrum difference determination unit 70 is supplied to a spectral transformation computer 80. This transforms the frequency difference using an inverse fast Fourier transform, IFFT for short, into an amplitude representation/time domain representation.

[0070] In the exemplary embodiment shown the spectral transformation computer 80 is a portable computer device. The IFFT is performed by means of known algorithms and is not to be described in greater detail at this point.

[0071] In one embodiment of the device (not shown), the spectral transformation computer 80 can additionally use also phase information determined by the SDR 50, for example of a frequency sweep, to determine the amplitude representation/time domain representation. This makes a line-length- or propagation-time-referenced amplitude representation possible.

[0072] The determined, in particular line-length- and/or propagation-time-referenced amplitude representation is supplied to an output unit for the temperature-dependent impedance curve 90 and is output by this.

[0073] In one variant the frequency spectrum difference determination unit 70, the spectral transformation computer 80 and the output unit 90 can be realised jointly by a portable computer device with screen, for example by a standard (portable) computer. The reference spectrum 60 can be stored by the computer device and/or provided by this.

[0074] FIG. 4A shows examples of temperature-dependent impedance curves output by the output unit 90. Here the signal propagation time and/or the cable length is plotted on the abscissa and the signal amplitude and/or the cable impedance on the ordinate in a coordinate system, wherein the signal propagation time and the cable length as well as signal amplitude or the cable impedance are each transferable into one another by the multiplication of constants, if the signal propagation velocity and the power of the multi-frequency signal are at least substantially constant.

[0075] If a first point T1 or a section of the cable 40 is heated, a local increase in the cable impedance takes place due to the heating. The rise in the cable impedance changes the line properties of the overall cable such that the frequency spectrum determined by the SDR 50 differs from the reference spectrum 60. If the frequency difference between the determined frequency spectrum and reference spectrum 60 is converted by means of an IFFT into an amplitude representation/time domain representation, then at the point T1 (if the abscissa is standardised to a cable length) a rise in the signal amplitude or cable impedance appears. The rise increases as the temperature rises. A change in the signal amplitude and the cable impedance over a period and/or different usage states of the cable can be used to discern a change in impedance caused by temperature and a change in impedance caused by damage.

[0076] Analogous to the increase in signal amplitude or cable impedance at the first point T1, a change in the signal amplitude or cable impedance represented at the open cable end E takes place due to the change in line properties of the overall cable. The cable impedance represented at the line end E does not correspond to the actual cable impedance at the cable end, as for a correct representation an unlimited frequency spectrum would have had to be sensed. The signal amplitude or line impedance actually represented at the cable end E changes with a rising temperature, however, by analogy with the signal amplitude or cable impedance at the heated first point T1 and can thus be used additionally to determine the temperature rise.

[0077] In addition, with a known cable length the abscissa can be standardised by the recognisable (variable) cable impedance at the open cable end E. In other words, the abscissa point with the recognisable (variable) impedance corresponds to the cable end E, so that an (at least approximate) standardisation of the abscissa is possible with a known cable length (if no complete cable separation/damage is present). This is advantageous primarily in embodiments of the device/method without propagation time or phase information determination. The standardisation can be carried out in particular also with the measurement of the reference spectrum on the reference cable.

[0078] FIG. 4B shows the effects of an extension of the heating to a section of the cable between a first point T1 and a second point T2, wherein the maximum of the heating is attained between the first point T1 and the second point T2. As a result, there occurs in the amplitude representation/time domain representation a rise in the signal amplitude or the cable impedance that extends by analogy with the heating along the cable.

[0079] An advantage in this case consists in the fact that even a complete uniform heating of the cable is identifiable and quantifiable by a rise in/an offset of the/to the signal amplitude or the cable impedance.

[0080] It is understood that the exemplary embodiments explained above are not conclusive and do not restrict the subject matter disclosed here. In particular, it is obvious to the person skilled in the art that he can combine the features described with one another in any way and/or can omit various features without departing from the subject matter disclosed here.