Measuring arrangement and temperature-measuring method, and sensor cable for such a measuring arrangement

Abstract

A temperature measurement is performed using a sensor cable. The measuring arrangement has a first signal conductor, a feed unit for feeding a measurement signal into the signal conductor, and an analyzing unit which ascertains and analyzes a change in the signal transit time of the measurement signal as a result of a temperature-induced change in a first temperature-dependent dielectric constant and is configured to derive a temperature signal from the ascertained signal transit time. The first signal conductor together with a second signal conductor forms the sensor cable, and each of the two signal conductors is surrounded by an insulation which is made of a first material that has a first dielectric constant in the first signal conductor and which is made of a second material that is different from the first material and has a second dielectric constant in the case of the second signal conductor.

Claims

1. A measuring configuration for temperature measurement, the measuring configuration comprising: a sensor cable having a first signal line and a second signal line, said first and second signal lines each being surrounded by an insulation, said insulation of said first signal line being made of a first material with a first temperature-dependent dielectric coefficient, said insulation of said second signal line being made of a second material being different from the first material and having a second temperature-dependent dielectric coefficient being different from the first temperature-dependent dielectric coefficient; a signal injector injecting a measurement signal into said sensor cable, said signal injector configured for a parallel injection of the measurement signal into said first and second signal lines; and an evaluator configured for evaluating a difference between a first transit time of the measurement signal injected into said first signal line and received at said evaluator and a second transit time of the measurement signal injected into said second signal line and received by said evaluator, and a temperature is derived from the difference between the first transit time and the second transit time, the first and second transient time being defined as a time necessary for the measurement signal to travel from the signal injector to the evaluator.

2. The measuring configuration according to claim 1, wherein said first signal line only contains said insulation of the first material in certain sections, and otherwise has said insulation of the second material for locally selective temperature measurement.

3. The measuring configuration according to claim 1, wherein the first material is selected such that the temperature-dependent, first dielectric coefficient changes by at least 1% for each 10 K of temperature difference.

4. The measuring configuration according to claim 1, wherein the first temperature-dependent dielectric coefficient demonstrates a temperature dependency that is greater than the second dielectric coefficient by at least a factor 2.

5. The measuring configuration according to claim 1, wherein: said sensor cable further has at least one resistive line made of a resistive alloy; and said evaluator is configured for evaluating a resistance of said resistive line and for deriving a further temperature from the resistance.

6. The measuring configuration according to claim 5, wherein said evaluator is configured for comparing and evaluating the temperature and the further temperature, and deciding, whether only a local hotspot or an even heating of said sensor cable is present.

7. The measuring configuration according to claim 1, wherein said evaluator is configured to evaluate a position of a local hotspot on said sensor cable, in that a transit time of a reflected signal component, reflected at a reflection location that is created by a local change in impedance as a result of a locally limited change, caused by temperature, in the dielectric coefficient, is evaluated.

8. The measuring configuration according to claim 1, further comprising an energy source; and wherein the measuring configuration is configured for use in an on-board electrical system of a vehicle, and in that at least one of said first and second signal lines of said sensor cable creates an electrical connection between said energy source and a load, for a transmission of electrical power.

9. The measuring configuration according to claim 1, further comprising a cut-out for reversibly disconnecting an electrical connection established by said sensor cable by means of said evaluator, wherein said cut-out is driven depending on the temperature measurement and is connected in at one end of said sensor cable.

10. The measuring configuration according to claim 1, wherein the temperature measurement is made continuously by means of said evaluator.

11. The measuring configuration according to claim 1, wherein the temperature measurement is made in real time, for ascertainment of an instantaneous temperature of said sensor cable.

12. The measuring configuration according to claim 1, wherein the temperature is a temperature of said sensor cable.

13. A method for temperature measurement, which comprises the steps of: providing a sensor cable having a first signal line and a second signal line, the first and second signal lines each being surrounded by an insulation, the insulation of the first signal line being made of a first material with a first temperature-dependent dielectric coefficient, the insulation of the second signal line being made of a second material being different from the first material and having a second temperature-dependent dielectric coefficient being different from the first temperature-dependent dielectric coefficient; injecting, via a signal injector, a signal into the sensor cable, the signal injector parallel injecting the signal into the first and second signal lines; receiving the signal at an evaluator being connected to the first and second signal lines, the evaluator determining first and second transient times being defined as a time necessary for the signal to travel from the signal injector to the evaluator; determining, via the evaluator, a difference between the first transit time of the signal injected into the first signal line and received at the evaluator and the second transit time of the signal injected into the second signal line and received by the evaluator; and deriving a temperature of the sensor cable from the difference between the first transit time and the second transit time.

14. The method according to claim 13, which further comprises: activating a pulse counter, being part of the evaluator, on arrival of the signal at the evaluator along one of the first and second signal lines; deactivating the pulse counter upon arrival of the signal along the other of the first and second two signal lines; and evaluating the pulse counter for determining a transit time difference.

15. The method according to claim 13, which further comprises: interrupting an electrical connection established by means of the sensor cable when a predetermined switch-off temperature of the sensor cable is reached, wherein the measuring configuration serves as a cable protection system.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a simplified illustration of a measuring arrangement;

(2) FIG. 2 is a simplified circuit diagram of the measuring arrangement;

(3) FIG. 3 is a diagrammatic, cross-sectional view of a sensor cable;

(4) FIG. 4 is a perspective view of a variant of the sensor cable;

(5) FIG. 5 is a perspective view of a further variant of the sensor cable;

(6) FIG. 6 is an end view of a further variant of the sensor cable; and

(7) FIG. 7 is a block diagram of an on-board electrical system into which the measuring arrangement is integrated.

DETAILED DESCRIPTION OF THE INVENTION

(8) Parts with the same function are shown with the same reference signs in the figures.

(9) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a measuring arrangement 2 for temperature measurement which contains a sensor cable 4, an injection unit 6 and an evaluation unit 8, 8. The measuring arrangement 2 is used in general for temperature measurement either of a temperature change or also the measurement of an absolute temperature, preferably with local resolution in the region of the sensor cable 4. In the exemplary embodiment, a part 8 of the evaluation unit 8 is illustrated on the side of the injection unit 6, and is configured to detect a reflected signal component R.

(10) A measurement signal S is injected by the injection unit 6 into the sensor cable 4 and ultimately, after passing along the sensor cable 4, is evaluated by the evaluation unit 8.

(11) The measurement signal S is, for example, a digital signal, wherein signal pulses P (see also FIG. 2) are injected in defined periods of time.

(12) FIG. 2 illustrates a variant embodiment in which the sensor cable 4 contains a first signal line 10a and a second signal line 10b, which are stranded together to form a conductor pair in the manner of a twisted pair and which are, for example, moreover surrounded by a screen and/or cable cladding.

(13) In addition to this conductor pair 10a, 10b, in an alternative variant embodiment, illustrated in FIG. 3, an additional second conductor pair with insulated resistive lines 12 is integrated into the sensor cable 4. The resistive lines 12 and the conductor pair 10a, 10b are stranded together in the manner of a quadruple stranding. The two signal lines 10a, 10b and the further resistive lines 12 are here arranged diagonally across from one another in the manner of a cross.

(14) The signal lines 10a, 10b are surrounded by a first material 14a or by a second material 14b as an insulation or also as a dielectric, wherein the two materials 14a and 14b have different dielectric coefficients. The resistive lines 12 are also surrounded by an insulation 16. The entire stranded assembly, i.e. the signal lines 10a, 10b and the resistive lines 12, with the respective insulations 14a, 14b and 16 are surrounded by a common screen 18 and by a cable cladding 20 immediately surrounding that. The screen 18 can be a multi-layer screen 18 comprising, for example, a braided screen as well as further foil screens.

(15) In the variant embodiment shown in FIG. 2, the measurement signal S is injected into both signal lines 10a, 10b in parallel, the signal propagating as the measurement signals S1, S2 in the two signal lines 10a, 10b. These continue along the sensor cable 4 until they reach the evaluation unit 8. This, for example, contains a comparator 22, with the aid of which transit time differences t between the two measurement signals S1, S2 are detected and processed to form a comparison signal V. This is then processed further, in a manner not presented here in more detail, in the evaluation unit 8 in order to generate, from the comparison signal V and from the transit time difference t that it represents, a temperature signal T which is output, for example, as a relative temperature change or also as an absolute temperature.

(16) When using the sensor cable 4 illustrated in FIG. 3 with the two insulated resistive lines 12, then the measurement signal S is in addition coupled into these resistive lines 12 by the injection unit 6, and correspondingly evaluated by the evaluation unit 8. The correspondingly configured evaluation unit 8 therefore contains at least one, and, in the case of the sensor cable according to FIG. 3, two signal inputs for resistive lines 12 and two signal inputs for the two signal lines 10a, 10b. The resistance of the respective resistive line 12 is ascertained through a resistance measurement, and a temperature signal T is also derived from this ascertained resistance value.

(17) Finally, yet another signal, namely the reflected signal R, is detected and evaluated by the evaluation unit 8. Such a reflected signal component R of the measurement signal S occurs in the case of a local hotspot 24, as is illustrated by the arrow in FIG. 1. Local hotspot 24 here means that a significantly higher temperature is present at this location as compared to the rest of the sensor cable 4.

(18) FIG. 4 shows a perspective illustration of a section of a variant of the sensor cable 4, wherein the second signal line 10b is implemented as a stranded conductor, and is surrounded by insulation 16 that is divided in a radial direction into two partial insulations 16, 16. The first signal line 10a is here arranged as a tape-like auxiliary line between the two partial insulations 16, 16, and is incorporated longitudinally. The two partial insulations 16, 16 are manufactured from the two different materials 14a, 14b, here in particular such that the inner partial insulation 16 is manufactured from the second material 14b and the outer partial insulation 16 is manufactured from the first material 14a with a temperature-dependent dielectric coefficient.

(19) FIG. 5 shows a section of a further variant of the sensor cable 4, also shown in perspective. In this variant, the insulation 16 of the first signal line 10a is only made of the first material 14a over a section A, and is otherwise made of the second material 14b, which is also used to make the insulation 16 of the second signal line. A local temperature sensor is constructed in this way, permitting locally selective temperature measurement. Both signal lines 10a, 10b are here additionally surrounded by a common cable cladding 20.

(20) A cross section of a further variant of the sensor cable 4 is illustrated in FIG. 6. The sensor cable 4 here contains a central line 25 with a plurality of cores 25. One of these cores 25 here in turn comprises the second signal line 10b, which is manufactured of insulation 16 of the second material 14b. The line 25 is surrounded by a cable cladding 20 in which a part, having the form of an annular segment, is implemented as an electrically conductive section E. In the variant illustrated here, an electrically conductive additive is added in a suitable manner for this purpose during fabrication of the cable cladding 20, in order to form the electrically conductive section E as the first signal line 10a. Alternatively, the outer cladding 20 is manufactured for this purpose in a strip extrusion method from two different materials. The remaining part of the cable cladding 20 is then manufactured from the first material 14a which correspondingly surrounds the first signal line 10a as insulation 16.

(21) The following different measurements and evaluations are altogether enabled with the measuring arrangement 2, and preferably are indeed carried out.

(22) a) Measurement and evaluation of a change in the signal transit time in the first single line 10a as a result of a temperature increase: the first signal line 10a is here surrounded by the first material 14a as a dielectric that exhibits a strong temperature dependency. In particular, the first material 14a is formed by a PVC cladding. The second signal line 10b, which is designed as something like a reference line, is not necessarily required. The change in the signal transit time can also be ascertained absolutely in comparison to an expected value. The evaluation unit 8 and the injection unit 6 are for this purpose synchronized to one another in respect of the injection of the measurement signal S, so that the evaluation unit 8 can ascertain differences in the signal transit time in comparison with an expected signal transit time.
b) Ascertaining the transit time difference t between the measurement signals S1, S2 using a sensor cable 4 with the first signal line 10a and the second signal line 10b.

(23) With this measurement setup according to FIG. 2, a simplified measurement through forming a difference of the two signals S1, S2 is permitted, whereby overall an improved reliability and greater precision are achieved.

(24) In both cases a), b) a temperature change is determined from the changed signal transit time. A clear distinction between a homogeneous temperature increase along the entire sensor cable 4 and a merely local hotspot 24 is not, however, enabled here. The two variants a), b) are both based on a change in the dielectric coefficient in the presence of a temperature change.

(25) c) Detection and evaluation of the reflected signal component R resulting from a local hotspot 24.

(26) In the event of a local hotspot 24 this, as already explained, leads to a rise in the impedance, so that a reflected signal component R is obtained at this hotspot 24. This is coupled, for example, into the screen 18 in the case of the sensor cable 4 according to FIG. 3, and in this case therefore is employed as something like a return line. The evaluation unit 8 has, for this purpose, a further return line connection to which, in this case, the screen 18 is connected. The evaluation unit 8 checks whether there is a signal present at this return line connection, and then identifies it as the reflected signal component R. The evaluation unit 8 ascertains a signal transit time, namely that between the injection of the measurement signal S and the detection of the reflected signal component R. The evaluation unit 8 then derives the position of the local hotspot 24 on the basis of the signal transit time for the reflected signal component R. The section 8 of the evaluation unit 8 does not necessarily have to be separated from the evaluation unit 8. The injection unit 6 and the evaluation unit 8, 8 can, in principle, also be positioned in one device at one location. The sensor cable 4 is, for example, in this case laid in the manner of a loop.

(27) d) Supplementary temperature measurement with the aid of the resistive line 12.

(28) The measurement signal S is, in addition, also injected into the resistive line 12, and the evaluation unit 8 ascertains the resistance value of the resistive line 12, which is also temperature-dependent.

(29) Through different combinations of these different measuring principles a) to d) it is possible to obtain different information.

(30) With the measuring principles according to a), b) it is possible to draw conclusions as to a mean relative change in temperature or also as to a mean absolute temperature of the sensor cable 4.

(31) Measurement principle b) allows the position of a local hotspot 24 to be located with local resolution.

(32) Through combinations of measuring principles a)/b) and c) a measurement of temperature with simultaneous local resolution is enabled.

(33) Measurement principle d) makes a second, independent measurement path available for ascertaining an averaged temperature change, or also of an averaged absolute temperature in the area of the sensor cable.

(34) Through combinations of principles a)/b) and d) it is furthermore possible to distinguish whether the temperature rise is a result of only a local hotspot 24 or of a homogeneous heating of the sensor cable 4.

(35) With a combination of all three fundamental measurement principles a)/b), c) and d) it is possible to determine whether just a local hotspot 24 is present and, in addition, its spatial location can be identified.

(36) Altogether, therefore, the measuring arrangement 2 described here permits an economical and very effective measuring arrangement 2 for temperature measurement with the aid of a sensor cable 4 of comparatively simple design.

(37) This measuring arrangement 2 is employed, in accordance with a first variant embodiment, for monitoring the temperature of cables. For this purpose the sensor cable, at least the individually insulated lines 10a, 10b and, in relevant cases, the resistive lines 12, are integrated together with further supply lines, data lines or even fluid lines and so forth, in a common protective sheath. Through this measure, therefore, a cable can be monitored for an unacceptable temperature stress, even if local. Further this measuring arrangement 2 is preferably employed in power engineering in order, for example, to identify defects, in particular in high-voltage cables, which lead locally to an increased line temperature. In addition to this, the measuring arrangement is generally also employed in process engineering for the temperature monitoring of machines, components etc., in order, for example, also to detect and measure temperature stratifications. On top of this, this measuring arrangement 2 is also preferably used in printed circuit board technology for temperature monitoring. The sensor cable 4 is as a whole characterized in that a temperature-sensitive sensor is formed over the entire length, and that separate individual sensors are not built into the cable.

(38) FIG. 7 shows schematically a section of an on-board electrical system 26 of a vehicle, not itself illustrated further. A measuring arrangement 2 is integrated into the on-board electrical system 26, in order to implement a cable protection system. Initially a sensor cable 4 is employed for the transmission of electrical power from an energy source 28 to a load 30. The transmission is performed, in particular, by at least one of the two signal lines 10a, 10b. In the exemplary application shown here, the energy source 28 is a high-voltage store of the vehicle, for the supply of an electrical drive machine; the vehicle is thus, in particular, an electric or hybrid vehicle. The load 30 here is a power distributor, which distributes the electrical power provided by the energy source to further loads, not illustrated in more detail.

(39) In order, in particular, to protect the electrical connection from overheating, the measuring arrangement 2 contains a cut-out 32, by which the connection can be interrupted. Such an interruption occurs, for example, if a certain temperature rise is measured in or at the sensor cable 4. The measuring arrangement 2 is here configured for temperature measurement by means of the transmission method in order to measure and monitor the temperature; the injection unit 6 and the evaluation unit 8 are arranged for this purpose at different ends of the sensor cable 4.

(40) The injection unit 6 then generates the measurement signal S which is transmitted by the two signal lines 10, 10b. Depending on the temperature along the sensor cable 4, a transit time difference t develops during the propagation between the two parts; this is measured by the evaluation unit 8 by a pulse-counting method, and used to ascertain the temperature. For this purpose the evaluation unit 8 contains an appropriate pulse counter 34. If the temperature exceeds a predetermined switch-off temperature, for example as a result of a particularly high current, the cut-out 32 is triggered, and the connection established by the sensor cable 4 is interrupted, in order to prevent damage to the sensor cable 4 as well, in particular, as to its surroundings through further heating.

(41) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 2 Measuring arrangement 4 Sensor cable 6 Injection unit 8, 8 Evaluation unit 10a First signal line 10b Second signal line 12 Resistive line 14a First material 14b Second material 16 Insulation 16, 16 Partial insulation 18 Screen 20 Cable cladding 22 Comparator 24 Hotspot 25 Line 26 On-board electrical system 28 Energy source 30 Load 32 Cut-out 34 Pulse counter A Section E Electrically conductive section S Measurement signal P Pulse t Transit time difference V Comparison signal T Temperature signal R Reflected signal component S1 Measurement signal in the first signal line S2 Measurement signal in the second signal line