Method and measuring system for monitoring a line for changed ambient conditions

Abstract

A method for monitoring a line for a change in ambient conditions. The line includes a measurement line of a predetermined length which has a measuring conductor enclosed in an insulation with a known dielectric coefficient. An analog signal of defined frequency is generated and injected at a feed site. The signal is reflected at a predetermined reflection site and a resulting signal amplitude is measured at a defined measuring point. A measure for the ambient condition, particularly a temperature, is determined from the signal amplitude.

Claims

1. A method for monitoring a line for a change in an ambient condition, the method comprising: providing the line with a measuring line having a predetermined length and including a measuring conductor surrounded by an insulation; generating an analog signal and feeding the signal into the measuring line at a feed site, the analog signal being a periodic, continuously changing signal with a given frequency with steadily rising or falling amplitude; reflecting the signal at a known reflection site, a reflected signal component being returned in the measuring conductor; measuring a signal amplitude at a fixed measuring site, wherein a changed ambient condition leads to a changed velocity of propagation of the signal and thus a shift in the phase of the signal at a fixed measurement location, so that the signal amplitude varies at the fixed measurement location and that the signal amplitude is a measure for the changed ambient condition; and ascertaining a measure for the changed ambient condition based on the signal amplitude at the fixed measuring site.

2. The method according to claim 1, which comprises forming a standing wave between the feed site and the reflection site.

3. The method according to claim 1, wherein the known reflection site is an end of the measuring line.

4. The method according to claim 3, wherein the end of the measuring line is an open end.

5. The method according to claim 1, wherein the changed ambient condition is a condition selected from the group consisting of a temperature, an attenuation of the measuring line, and an insertion lass of the measuring system.

6. The method according to claim 1, which comprises generating the signal at a frequency from greater than 10 KHz to a multiple of 100 MHz.

7. The method according to claim 6, which comprises generating the signal at a frequency in a range from 200 MHz to 500 MHz.

8. The method according to claim 1, wherein the measuring line is a supply core conducting a current and the feeding step comprises superimposing the analog signal on the current.

9. The method according to claim 8, wherein the current transmitted on the measuring line is a direct current.

10. A measuring system for monitoring a line for a changed ambient condition, the measuring system comprising: a measuring line having a predetermined length and including a measuring conductor surrounded by an insulation; a signal generator for generating an analog signal with a predefined frequency, the analog signal being a periodic, continuously changing signal with a given frequency with steadily rising or falling amplitude; a voltmeter for measuring a signal amplitude at a fixed measuring site on said measuring conductor, wherein a changed ambient condition leads to a changed velocity of propagation of the signal and thus to a shift in the phase of the signal at a fixed measurement location, so that the signal amplitude varies at the fixed measurement location and that the signal amplitude is a measure for the changed ambient condition; and an evaluation unit connected to receive the signal amplitude and configured for ascertaining a measure for the changed condition based on the signal amplitude measured at the measuring site.

11. The measuring system according to claim 10, wherein said measuring line is open at one end thereof.

12. The measuring system according to claim 10, wherein said measuring line extends in a component to be monitored.

13. The measuring system according to claim 12, wherein said measuring line is configured for monitoring a temperature prevailing in the component.

14. The measuring system according to claim 10, wherein said measuring line is a supply core.

15. The measuring system according to claim 10, wherein said measuring line is a supply core of a charging cable.

16. The measuring system according to claim 12, wherein the component is a component selected from the group consisting of a cable, a thermally loaded component, and a compound that changes as a result of an exothermic or endothermic reaction.

17. The method according to claim 1, wherein the ascertained measure for the changed ambient condition is based only on the signal amplitude, and selectively drawing a conclusion as to the changed ambient condition from the signal amplitude by way of an algorithm, or by a comparison to comparison values or reference values for the measured signal amplitude.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The FIGURE shows a measuring system comprising a measuring line and having different signal profiles in a highly simplified, schematic representation.

DETAILED DESCRIPTION OF THE INVENTION

(2) The measuring system 2 shown in the FIGURE comprises a signal generator 4, a voltmeter 6 and a measuring line 8 as essential components. The internal resistance of the signal generator is adapted to the surge impedance of the measuring line 8. The measuring line 8, in turn, comprises a central measuring conductor 10, which is surrounded by insulation 12, applied in particular by way of extrusion coating, having a known, temperature-dependent dielectric constant. In addition, the measuring line 8 preferably also includes a shield, which forms an outer conductor, which is preferably connected to a ground terminal 14 having a defined reference potential, and in particular ground potential. The measuring line 8 can be a coaxial cable, for example.

(3) An analog signal, specifically a sinusoidal or cosinusoidal signal having a particular predetermined frequency, for example in the range between 1 and 1000 megahertz, is generated by way of the signal generator 4. The frequency of the signal is kept constant during the measurement, and is not changed. The generated signal is fed into the measuring conductor 10 at a feed site 16 and travels through the entire length of the measuring conductor 10, to a reflection site 18 at which at least the majority of the signal is reflected, whereby a reflected signal is generated and returns in the measuring conductor 10. The reflection site 18 is an open line end, for example, that is, the measuring conductor 10 is electrically contactless at this end. Due to the special design, the length between the feed site and the reflection site 18 is thus known.

(4) Moreover, the voltmeter 6 is designed to tap the signal amplitude at a fixed, defined measuring site 20.

(5) A standing wave, as is shown in the bottom half of the FIGURE, is created within the measuring conductor 10 due to the high degree of reflection at the reflection site 18. The illustrated waves are envelopes. The FIGURE illustrates an idealized behavior of the measuring line without attenuation. In a real line, the amplitude of the reflected signal is lower due to attenuation.

(6) As a result, the “amplitude of the envelope” decreases under the influence of attenuation. Likewise, less signal energy is fed in the case of a mismatch (insertion loss). These effects are not shown in the simplified FIGURE.

(7) Due to the temperature dependence of the dielectric constant of the insulation 12, the velocity of propagation of the signal within the measuring line 8 changes with the temperature. The two sinusoidal signal profiles shown schematically in the bottom half of the FIGURE indicate the location-dependent amplitude for two different temperatures. When the temperature changes, the phase position of the signal shifts, so that a noticeable change of the signal amplitude occurs at the fixed measuring site 20. The length of the two indicated arrows, which are directed at the two signal profiles at the measuring site 20, represent the respective signal amplitude measured for the particular signal profile at the measuring site 20.

(8) The voltmeter 6 is furthermore connected to an evaluation unit, which is not shown in detail here. Conclusions as to the prevailing ambient condition, and in particular the temperature, are drawn in this evaluation unit based on the measured signal amplitude. This takes place, for example, by a comparison to stored reference data. In general, it is thus possible to detect the velocity of propagation, for example, and, derived therefrom, the temperature in the surrounding area of the measuring line or the measuring line itself, based on the signal amplitude.