Method for monitoring a line for unchanged ambient conditions and measuring arrangement for monitoring a line for changed ambient conditions

Abstract

A method monitors a line for changed ambient conditions. The line has a measuring line with a predetermined length and a measuring conductor surrounded by insulation having a known dielectric constant. In the method, an analog signal having a predetermined frequency is generated, the signal is divided into a reference signal and an operating signal, the operating signal is fed into the measuring conductor, a return signal obtained from the operating signal is combined with the reference signal and by a phase shift between the reference signal and the return signal, a measure is determined for the changed condition, particularly for a temperature change.

Claims

1. A method for monitoring a line for changed ambient conditions, the line having a measuring line with a predetermined length and a measuring conductor surrounded by insulation, which comprises the steps of: generating an analog signal being a periodic signal having a predetermined frequency; dividing the analog signal into a reference signal and an operating signal; feeding the operating signal into the measuring conductor; combining a return signal obtained from the operating signal with the reference signal, wherein the return signal, under normal conditions, having a run time to be expected and under ambient conditions deviating from the normal conditions, a maximum run time difference to be expected and wherein a frequency is tuned to the maximum run time difference to be expected in such a manner that a phase shift is 180 by amount; and determining a measure for a changed condition by means of a phase shift between the reference signal and the return signal.

2. The method according to claim 1, which further comprises amplifying the return signal in such a manner that the return signal has a same amplitude as the reference signal.

3. The method according to claim 1, wherein the return signal is a reflected component of the operating signal and the measuring line is a spur line.

4. The method according to claim 1, which further comprises coupling the return signal into a return conductor separate from the measuring conductor.

5. The method according to claim 1, which further comprises forming the analog signal as a sinusoidal signal having a predetermined frequency.

6. The method according to claim 1, wherein the phase shift is 90.

7. The method according to claim 1, wherein the phase shift is 45.

8. A method for monitoring a line for changed ambient conditions, the line having a measuring line with a predetermined length and a measuring conductor surrounded by insulation, which comprises the steps of: generating an analog signal being a periodic signal having a predetermined frequency; dividing the analog signal into a reference signal and an operating signal; feeding the operating signal into the measuring conductor; combining a return signal obtained from the operating signal with the reference signal, wherein the return signal, under normal conditions, having a run time to be expected and under ambient conditions deviating from the normal conditions, a maximum run time difference to be expected and wherein a frequency is tuned to the maximum run time difference to be expected in such a manner that a phase shift is 180 by amount; and superimposing the reference signal and the return signal to form a resultant signal and from an amplitude of the resultant signal, a measure is determined for a changed condition.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a schematic diagram showing a first variant of the embodiment of a measuring arrangement according to the invention;

(2) FIG. 2 is a schematic diagram of a second variant of the embodiment of the measuring arrangement; and

(3) FIG. 3 is a schematic diagram of a third variant of the embodiment of the measuring arrangement.

DETAILED DESCRIPTION OF THE INVENTION

(4) In the figures, identically acting parts are provided in each case with the same reference numerals.

(5) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a measuring arrangement 2 which has a monitoring unit 4, to which a measuring line 6 is connected. The monitoring unit 4 therefore forms a structural unit. Within the monitoring unit 4, a signal generator 8, a splitter 10, a comparator 12 configured, in particular, as differential amplifier, a voltage meter 14 and an evaluating unit 16 are integrated. Additionally, an amplifier 18 and a coupling element 20, which is preferably formed as a directional coupler, are optionally integrated.

(6) The measuring line 6 which is in particular formed as a spur line is connected to the monitoring unit 4, for example to a suitable terminal 21 such as, e.g., plug-in contact.

(7) The measuring line 6 is in the illustrative embodiment of FIG. 1 a single-core line with one core, that is to say with one measuring conductor 24 surrounded by an insulation 22. Due to its design as a spur line, one end of the measuring line 6 is open and the measuring conductor 24 is therefore not electrically contacted.

(8) The signal generator 8 generates a periodic alternating-voltage signal S, particularly a sinusoidal signal. This is divided in the splitter 10 into a reference signal R and into an operating signal LS. The operating signal LS is subsequently fed into the measuring conductor 24. In the illustrative embodiment, an internal conductor path is formed within the monitoring unit 4 which is led from the splitter 10 via the coupling element 20 to the terminal at which the measuring conductor 24 is connected.

(9) The operating signal LS is reflected at the open end of the measuring line 6 because of the design as a spur line. The reflected component is propagated as return signal RS within the measuring conductor 24 in the opposite direction to the operating signal LS. The return signal RS is coupled via the coupling element 20 into a return conductor 26 within the monitoring unit 4. The return signal RS then coupled in is amplified via the optional amplifier 18 and supplied to a first input of the comparator 12. The reference signal R is present at a second input of the comparator 12. The comparator 12 generates a resultant signal S by summing or differentiating. The amplitude thereof is detected via the voltage meter 14 and supplied to the evaluating unit 16 as voltage measuring signal.

(10) In the variant of the embodiment according to FIG. 2, the measuring line 6 is replaced by a two-core line provided, in particular, with a shielding 28. The conductors of the two cores are connected to one another in this case at their ends. The conductors of the two cores together form the measuring conductor 24.

(11) In this arrangement, one core is connected to the terminal 21 of the monitoring unit 4. Thus, the operating signal LS is fed from the splitter 10 into this core. The other core is connected to a further terminal 29 of the monitoring unit 4 configured as an input and is connected to the first input of the comparator 12 within the monitoring unit 4 via a conductor path. The reference signal R, in turn, is present at the second input of the comparator 12. As also in the variant of the embodiment according to FIG. 1, the voltage (amplitude) of the resultant signal Sr is measured and provided to an evaluating unit 16 by the voltage meter 4. In the variant of the embodiment of FIG. 2 the amplifier 18 is omitted in the illustrative embodiment.

(12) In this variant of the embodiment the return signal RS which is present at the first input of the comparator 12 is identical to the operating signal LS, i.e. the operating signal LS is virtually looped through the measuring line 6 via the two short-circuited conductors of the measuring line 6 and supplied as the return signal RS to the first input of the comparator 12.

(13) FIG. 3, finally, shows a further, particularly simple variant of the embodiment in which a conductor of the measuring line 6 as measuring conductor 24, is connected, on the one hand, to a feed-in side on the side of the signal generator 8 and, on the other hand, to a receiver side on the side of the evaluating unit 16. In the illustrative embodiment, the measuring conductor 24 is connected to the two terminals 21, 29. The measuring line 6 is, for example, a coaxial line or also a two-wire line. In the coaxial line, one of the conductors (inner conductor, outer conductor) is the measuring conductor and the other one is preferably connected to reference potential (ground). In the case of the two-wire line, one of the conductors is also the measuring conductor 24 and the other preferably connected to reference potential.

(14) The measuring arrangement 2 is particularly used for monitoring the measuring line 6 for a changed condition. This can be an external ambient condition or also an internal condition of the measuring line 6 itself. For this purpose, a state parameter, especially an ambient parameter, is monitored with the aid of the measuring arrangement. This state parameter is particularly the temperature.

(15) In this context, the measuring principle is based on the fact that the propagation of the measuring signal coupled in within the measuring line 6 and thus a run time of the return signal RS also depends, among other things on the dielectric constant of the insulation 22. The dielectric constant is in turn temperature-dependent so that the run time of the return signal RS is temperature-dependent. The run time of the return signal RS is understood in this case to be the total time which the signal (operating signal LS plus return signal RS) needs for the path between the output of the splitter 10 up to the first input of the comparator 12.

(16) Investigations have shown that, for example in the case of an ambient temperature of minus 40 C., the signal speed of the propagating signal is approximately 6 ns per meter and with an ambient temperature of 105 C. 8 ns per meter.

(17) The measuring line 6 has a defined predetermined length L overall. This length in this case is traversed in both variants of the embodiment. If the length L is for example 10 m, then the run path for the signal is 20 m.

(18) Assuming a maximum range of values to be monitored for the state parameter to be monitored, presently, for example, a maximum of about 145 for the temperature to be monitored (40 C. to 105 C.), a difference in operating time between the minimum temperature and the maximum temperature of, for example, 40 ns is to be assumed overall with a line length L of 10 m. This corresponds to a maximum difference in operating time t to be expected.

(19) The signal paths for the reference signal R and the measuring signal (operating signal LS plus return signal RS) differ appropriately by the signal path via the measuring line 6. The signal paths within the monitoring unit for the reference signal R, on the one hand, and for the measuring signal, on the other hand, are therefore preferably identical. Overall, the signal paths for the reference signal R and the measuring signal are selected in such a manner that when the two signals are combined at defined normal conditions (e.g. at 20 Celsius), a defined predetermined phase shift of, for example, 90 or also 270 occurs at a medium run time of presently, for example, 7 ns.

(20) Generally, the electrical signal path extended by the measuring line 6 leads to a defined shift in the phase angle of the return signal RS in comparison with the reference signal R. The amplitude of the resulting signal Sr changes, therefore, in dependence on the phase angle of the two signals R, RS with respect to one another. Since this depends on the temperature, in turn, it is possible to infer the temperature also directly from a phase change.

(21) Especially in the case of a steady signal, particularly a sinusoidal signal, the two signal components are superimposed linearly at the inputs of the comparator. Overall, a change in voltage of the resultant signal Sr results which is at least essentially proportional to a temperature change.

(22) To provide for an unambiguous evaluation, the frequency of the signal S generated is also selected in such a way that with the maximum difference in operating time t to be expected, only a predetermined maximum phase offset occurs between the two signals. This maximum phase offset is preferably +/90 and preferably +/45.

(23) In the above example, in which a maximum difference in operating time t of 40 ns is to be expected and with a desired maximum phase shift of 90 (+/45), a duration of the period of 160 ns is thus obtained for a 360 period. From this, a frequency for the signal of about 6.25 MHz is obtained in the exemplary embodiment.

(24) If the line length L is changed by a factor of 10 the frequency of the signal S to be fed in also changes by the factor 10, the frequency being reduced with increasing length L of the measuring line 6.

(25) The measuring line 6 is led in this case within a component 30 to be monitored. This is, for example, a cable so that the temperature loading of the cable is thus measured and monitored. In dependence on this temperature monitoring a life span to be expected or the wear of the cable is suitably inferred.

(26) In a second embodiment, the component 30 is a constructional unit to be monitored.

(27) According to a third variant of the embodiment the measuring line 6 is embedded within a compound. The compound is, for example, concrete, i.e. the measuring line 6 is also concreted in. Via the entire measuring arrangement 2, a temperature can then be monitored during the setting of the concrete.