DE1591928A1 - Method for measuring path lengths and propagation speeds, in particular for measuring errors and locating cables - Google Patents

Description

Methods for measuring path lengths and propagation speeds, especially for fault measurement and location on cables.

For several decades, there has been a lack of localization the so-called pulse echo method was implemented in cables. Be strict with her periodic repetition of voltage pulses at the input of the cable to be measured and the time interval between these voltage pulses and the cable faults or cable wave resistance irregularities of reflected echo pulses measured.

This tried and tested measurement method fails with long cable lengths because of the strong attenuation, to which measurement pulses in particular are subject to a very short period of time, which, on the other hand, are to be preferred for metrological reasons.

To remedy this problem, it has been suggested that each Reflection pulses arriving later are amplified more than those arriving earlier. This approach has proven to be very effective.

It was asked whether this problem occurred with other measurement methods easier and better way can be solved and whether with such other possible The measurement method has not overcome further difficulties of pulse chomethdoe can be. These difficulties include, for example, a sufficiently precise adjustment of the pulse generator to the cable input, which for a large; 2 frequency bandwidth and must be performed down to very low frequencies. This also includes that problem of the label simulation in the input circuit and a cheap one Signal-to-noise ratio, which in turn is due to the large bandwidth required for the Echo signal amplifier encounters difficulties.

Another advantageous solution to locating faults on cables is through given the invention described below.

It ties in with a well-known measuring method. It became a determination the height of aircraft above the ground. The procedure consists in to use an alternating voltage as a signal, the frequency of which is strictly proportional to time and is changed periodically. Because of the depending on the height above the ground The transit time occurs when the echo signal reflected on the ground is received at its Overlaying the emitted echo signal is a difference tone, the frequency of which is height-dependent and can be calibrated according to the height.

A direct transfer of this known method to the Measurement of wave impedance irregularities in cables is not possible, Because there are too many reflection points in such cables and because of the detection the nature of the reflecting points in each case is important for the cable measurement is.

According to the invention, a flow process is used for simplification and improvement provided, which consists in that an alternating voltage, preferably periodically floating frequency, which is used as the measurement signal, and which is reflected at points of interference and in the time more or less strongly delayed portion of this low signal, preferably after amplification in a selective amplifier, in a superimposed circuit when passing through the frequency of this over lagerers with known circuits overlay pulses generated as "quasi" echo signals on the time axis of a cathode ray image or other known writing device.

In the drawings are exemplary embodiments of the invention Procedure shown. starting from an alternating voltage generator 1 in Fig. 1 with a fixed frequency, a sawtooth generator 2 is controlled via the power 24. For a more detailed explanation of this, reference is made to Figs. 2a and 2b. Fig. 2a shows the alternating voltage amplitude of the generator 1 on the line 24 as a Tii-iiktion of time, £; bb. 2b the voltage curve of the sawtooth generator, 2 on the line 25. Do one the known voltage limiter circuits 3 is at a suitably selected time point t4 in Fig. 2b, the increase in voltage is limited, so that on the line 26 the voltage curve also shown in Fig. 2b 26a results. A voltage-dependent generator 4 will hit him a preferably very high freshness (for cable window measurements in the Aegel about 10 to 5 @ @@ z) controlled in its frequency. This control creates a time-dependent one frequency curve on line 27 of @bb. l according to Fig. 7. burch e @@ e the hindered Torque switching 5 is only a freely selectable one of this time-dependent frequency curve Time interval, e.g. between @@@ t1 and t @, let through. For setting the time interval from to t2 the @bb. 2b and 2c serves the @bc -; tte0 SieffiT es J'r)? ä £ t1fl £ GV £ 3: lcu35 before ¼- £ ez '. .Lcemator 2 ouro @ di @ @voltage limiter circuit 3. It becomes --1 ~~ r? C ---. g-e u0bCll)? fl1l? ) Tcrst1rlerstt? -? U- 12 and 1, via @@ itungen 32 and 43 prepared according to known @circuits @o @, there is a reverse voltage on the line 43 or 34 stands for the gate 5, as shown in Fig. 2c. That neat the alternating voltage signal generated according to the frequency curve during the time segment @ t1 to t4 according to Fig. 3 a frequency rising from f1 to f2, for example, is optionally transmitted via a power amplifier 6 via line 2 @ of Fig. 1 and via line 29, preferably via one Balancing transformer 7 and one of the switching elements 8,9,10 (real and reactive resistances) and the cable 11 formed bridge circuit to the cable input $ Toer the line 30 led This signal voltage becomes through regulation at the bridge branch lo kept away from the line 48 or compensated to the extent that high primary signal voltages can be used without that at the input of the selective amplifier 18 inadmissible high stress maplitudes can occur. The one via the cable entry connection 8, 9 and lo via the Loi @ u @@ 30 signal change voltage running into the cable @en @it a frequency that increases periodically from F1 to f2 is caused by cable faults reflects and arrives via the Beit @@@ 4 @ and the amplifier 10 on the line 47 and from her @@ a preferably additive superimposed 17. @ Em as @e reflected and alternating voltage with a time delay with respect to the signal voltage on the input side with the fixed @e @@@@@ z f2 'of an Oszillstorr 35 45er the line 60 superimposed. The frequency f2 'will be @ cm according to Fig. 3 preferably @ @@ g @ selects that it a a little below the @@@@@@@@ f2, up to which the generator 4 is controlled.

Via either @@@@ susenaltun. a partial voltage of the signal of the @@@@@@@ @@@@@@ the connection 29a to a voltage divider un @ @@@@@ @@@@ @@@@ @@@@@@@@@ 29c can optionally use this partial voltage via @@@ @@@ tung 29b in the output of the selective reinforcement @@@@ @@ @@@@@@@@ @@@@@. With this coupling unstent @ein @@@@@@ @@@ de @ in the frequency continuous @@@@@@@@@@@@@@ @@@@@ the fixed Frequency f2 'of the generator voltage from the oscillator 35 via the line 46 the rectifier and preamplifier 16 a voltage impulse, the as Zero pulse over the line 45 two @ -measure the perpendicular deflecting plates one Brau'solen tube 27 is supplied. It determines the beginning of the eating time. Each reflection pulse on the Eabelstrek-Ee travels at a later point in time to run through the frequency f2 of the fixed generator, as shown in Fig. 3 is shown for an echo that is currently t3 arrives at the cable entry and z. Zt. Tr ' leads to a pulse at the output of amplifier 16. It provides a "quasi" echo pulse on the screen of the tube 23. The amplifier 18 can be used as a more selective Amplifiers are generally designed with a relatively low bandwidth, while the rectifier and amplifier 16 must be made very broadband. The time measurement interval extends from the time pulse to about the point in time t5 in Fig. 3.

To produce the horizontal deflection of the cathode ray in the Braun tube of Fig. 1 is from the line 24 via the lines 31 and 38 the alternating voltage of the generator 1 is fed to a phase shifter 20.

This phase shifter is preferably a known die monostable multivibrator 21 controlled by the voltage pulses in the time domain of the measuring interval and by means of the phase shifter 20 in a known manner can be pushed away over the entire ness time. The tension curve on the line 41 is shown as an example in Fig. 4a and that in the monostable Multivibrator 21 generated pulse voltage in Fig. 4b. Hit the pulse voltage A deflection voltage is then generated in the multivibrator 21, for example via the line 42, in a known manner generated in the deflection voltage amplifier 22 for the bedding 44 to the Braun tube 23. Illit you can through the phase shifter 20 and the monostable hultivibrator 21 specific time intervals for the time axis writing over the entire deflection width of the Braun tube can be expanded to display it. For visualization of the time segments tX and tX 'of FIGS. 4b and 40 thus extracted is preferred n with the same voltage pulse from the multivibrator 21 via the line 57 of the Beam current of Branun's tube 2 @ gated in a known manner.

The point in time of the @overlay in overlay 17 touching and in the amplifier 16 generated "@uasi" echo impulses on the Schi @@ picture of the Braum'schen Tube 23 is from the phase of the high-frequency alternating voltages from the generator 4 and the Gseillator 35 somewhat dependent. This o'1 '; üs: ig;' time can indeed uVc1 suitable ij-e5 i reducing the rate of change of frequency of the generator 4 and the duration of the periphery of the generator 1 are small, but require very high accuracy their fixation.

In order to achieve this fixation, the phase shifters 14 and 19 - of Fig. 1, which - controlled by the power 31 via the lines 36 and 37 two alternating voltages according to Figs. 5a and 5b so in phase with each other shifted so that, for example, a time interval is reduced with the ITull crossings Fig. 5c from t5 to t8 is marked, in which, for example, a bistable Multivibrator 15 via lines 39 and 40 a blanking pulse for the generator 4 and the oscillator 35 via the line 33 supplies. At the end of this time interval At the time tS, the generator 4 and the oscillator 35 are then activated by the multivibrator 15 keyed up to time t7 or t5. Pü the time interval t8 to t2 or in the preceding period t1, the frequency of the generator 4 is increased the frequency f1 fixed to. then again proportional to time from the point in time t1 or t2 to rise.

A simpler implementation of the inventive idea is shown in Fig. 6 reproduced. In it is on the circuit units 3, 12, 14, 19 described above and 20 of Fig. 1 have been omitted. 70 is a known clipping circuit for the sawtooth voltage of 2, with which the time interval t4 to t2 of Fig. 2b and 2c is determined by setting a bias and with which at the same time the blocking of the alternating signal voltage of the generator 4 via stage 13 the gate 5 is to be effected via the line 34. Those with the clipping circuit 70 The sawtooth voltage that has been cut out is transferred to a for the time interval t4 to t2 known cutting circuit 71 continued. In it, a part of the Sawtooth voltage removed according to the voltage curve shown in Fig. 4c and fed to the horizontally deflecting plates of Braun's tube 23. This cutout is also slidably displaceable in a known manner preload Can be moved as required within the total time measurement range. To light the Cathode ray of the 3raun1's tube 23 is then used again by one of the known ones Hultivibrators 21 over the jjeituug 57.

In order to be able to solve the problem with the described Hess procedure, amplify the signals coming from more distant reflection points in the cable more to be able to than those arriving from closer places, we d the circuit of Fig. 1 according to Fig. 7 further developed. In it is a section of Fig. 1 reproduced of this; contains development. ; it consists in that not only the generator 4 in frequency through the saw tooth generator 2 via the Line 25 and optionally controlled by the voltage limiter circuit 3 is, but also the superimposed 35 via line 59 for the superimposed stage 17th

The fixed frequency becomes the superimposer 35 with a sliding frequency Oscillator 35 of Fig. 1 replaced.

The control of the frequency of the superimposer 35 is now according to the Representation in Fig. 8 with a much lower frequency change rate performed as this is necessary for the generator 4. Accordingly, on the Line 60 an alternating voltage with a frequency change according to curve 60 in Fig. 8 is available as a function of time and on line 27 a curve 28 as shown in Fig. 8. Therefore, for example, at time tr in Fig. 8, there is a reflected signal from the cable back and via the line 47 to the superimposed 17 according to Fig. 7, then there is a sequence matching with the superimposed frequency from the Superimposed 35 at a point in time t11 at a frequency f11 according to FIG. 8. Each The reflection signal arriving later from the bel becomes a later one accordingly Point in time and at a correspondingly higher frequency with one of the frequencies the superimposed 35 come into agreement.

The output from the superimposer 17 of Fig. 7 via the amplifier 16 of Fig. 1 "Quasi" echo signals arriving at the Brauntsche tube 23 are therefore temporal arrive in an orderly fashion. At the same time, the later comes a different and higher frequency of agreement with the alternating voltage from the superimposer 35. Those from more distant points of reflection of the Eabel arriving echo signals can thus be easily converted into their amplitude can be increased compared to those arriving earlier that the selective one Amplifier 18 is equipped with a corresponding frequency response.

To achieve the same phase conditions for the seginn des Swinging of the generator 4 and the superimposer 35 is also expedient as in Fig. 1, the keying pulse from 15, drawn via line 33.

The control of the generator 4 and the superimposed 35 can according to Fig. 9a and 9b also directly through the sinusoidal alternating voltages from the generator 1 take place. Then the sinusoidal control voltage for the superimposed 95-opposite of those for generator 4 shifted in phase, as shown in Fig. 9a for the alternating voltages 51 and 50 on lines 27 and 60 shows then, approximately at time t1, the channel opening for the voltages can be opened via line 34 be carried out on line 28.

In this way, signals from the cable reflected the frequency of the overlay 35 can overflow, the frequency deviation of the frequency control of the superimposed 35 according to curve 50 of Fig. 9a is kept smaller than that for the generator 4 according to curve 51 of Fig. 9a.

For the process described, it comes to representation and generation the "quasi" echo pulses for identifying cable reflection points on that Frequency interval in which the frequency of the reflected signal with the chewing of the superimposed 35 can come into the superimposed 17 in accordance. For one fixed superimposed frequency f2 ', as shown in Fig. 3, this means that only the immediate vicinity of f2 'in generator 4 is required as a signal for the cable will. All other alternating voltage frequencies are used for the formation of superimpositions in the superimposed 17 to generate a "quasi" echo without particular concern and stalks only meaning for waking the signal length. For an overlay 35 with controlled Frequency this range is somewhat larger, but can affect the frequency deviation of the superimposed 35 remain limited. A graph for that in this case frequency control to be provided for the generators 4 and the superimposer 35 is in Fig. 10 with the curves 52 and 53 reproduced. In it is preserved the rate of change of frequency for frequency control of the generator 4, this control is only required for the frequency range f1 to f2. Only one AC voltage signal then flows into the cable 11 with one in the time interval t1 to t of curve 52 in Fig.

10 shown history. In contrast, the control of the superimposed 35 extends to time t5.

A reflected signal that arrives at the cable entry at time tr, then leads to a superimposed pulse at point t1 'and accordingly later arriving at later times. Through the frequency control of the superimposer 35 at the same time a time expansion occurs in the reproduction of the "quasi" echo impulses, because the superposition due to its frequency dependence on a time expansion in the Reproduction of the reflection points leads.

For very high accuracy requirements, it is advisable to adjust the voltages of the superimposer 17 with the frequency-controlled voltage of the generator 4 and 35 to be coupled phase-locked. An exemplary embodiment is shown in FIG. 11.

The frequency controlled by the sawtooth generator 2 via line 26 Generator 4 is, for example, in a frequency range f1 to f? preferably Time-proportional and periodically shifted. About frequency divider 61 and 62 after Fig. 11, which are connected directly to the generator 4 via the line 66 and indirectly 67 f1 and f "are reduced to fl / n and f" / n, respectively. Via the line 68 becomes the frequency that moves periodically from f '/ n to ft' / n with a fixed frequency an ossillator 63 of e.g. f '/ n in a superimposed 65-superimposed via the line 73, so that on the line 60 a sliding frequency with the frequency deviation 2. f '/ n to 2 # f '' / n is available.

Let the sliding frequency of this stroke be the frequency curve in Fig. Lo correspond to curve 53 from frequency 2f '/ n to 2f' '/ n. This sliding frequency is used for overlaying in the overlay 17 according to Fig. 1. The one from f 'to fit sliding frequency in generator 4 (see Fig. 10) is transmitted via line 69 e.g. a frequency doubler stage 58-supplied, so that on the line 70 one of 2f1 up to 2f '' sliding frequency is available. You will be on line 70 a mixer 59 passed on and there with a fixed frequency from a multiplier stage 64 overlaid via line 71. The frequency in stage 64 is multiplied by a multiplication the sequence of a superimposer 63 of fixed frequency f '/ n with a multiplication factor (2n-2) f '/ n won. as a result, a sliding frequency falls on the line 27 a frequency deviation an of 2f '- (2n-2) f' = 2f 'n n up to a frequency of 2f' '- (2n-2) f / n' = 2 (f '' - f ') + 2f' / n.

This frequency deviation on the line 27 is therefore opposite to that on the Line 60 larger by a factor of n. On the other hand, those are sliding in frequency Alternating voltages on lines 27 and 60 in their phases with one another coupled.

Since according to the above statements for the signal formation of "quasi" echoes only a part of the frequency deviation on the line 28 for the output amplifier 6 is required is done via the circuit groups discussed above in terms of their functionality 3, 12 and 13 in gate 5 a blocking of the signal from the mixer 59 for the line 29 for the time interval t4 to t2 according to Fig. 10. A blanking is carried out via line 33 of the generator 4 in the time interval t5 to t8 of Fig. Lo carried out and an oscillation with a fixed frequency and phase at time t8 bist2 or t1 ensured how this has already been explained in connection with Fig. 1. Hence this will be in the cable 11 of the bb. 1 in the time t1 to t4 of Fig. 10 with a frequency deviation f2 -inlaufende Signal reflected so that it comes back at time tr, then arises at a point in time tr 'a superimposed pulse as a "quasi" echo signal. All of the available Ifees time extends from t1 to t5 in Fig. 10.

Instead of controlling the frequency of the generator 4 and the fixed one Oscillator 35 in Fig. 1 and the controlled overlay 35 in Fig. 1 and 7, instead of increasing frequency changes, decreasing frequency changes can also be used.

-This can increase the reflection signals from distant noise points be advantageous for dimensioning the frequency response of the amplifier 18.

The measuring method described offers a limitation because of its high degree of flexibility of the input signal for Eabel measurements to a possible much lower Bandwidth than is the case with the echo pulse method, both a better one Adaptation to or cable input as well as a better measurement of interferences of a higher impedance nature because of the more favorable signal-to-noise ratio. Also leads a superposition of the measurement signal with low-frequency alternating voltages greater Amplitudes to achieve changing reflection factors at points of failure to none Obstacles to the measurement and can therefore be used in particular to order high-resistance Defects are applied.

The above considerations were tacitly assumed that the voltage amplitude of the hot signal to the generator 4 is constant is. To narrow the frequency bandwidth for the selective amplifier 18 can However, in special cases it may also be advantageous to adjust the amplitude of the generator 4 to be steered roughly according to a bell curve.

The Hess method described should not apply in its application fault measurement and location on cables will be limited. A particularly interesting one Area of application offers the propagation of acoustic waves, i.e. sound waves for example, in sea water for sin measurement of sound-reflecting objects or water or sediment layers. Instead of the cable, a analog Circuit a sound transmitter 74 and sound receiver 75 according to Fig. 12a and 12b are used in a sound medium 76 to be examined for reflection bodies or layers. The sound transmitter 74 and the sound receiver 75 can, if the input circuit is balanced, As explained in Fig. 1, reduced to a transducer element 75a according to Fig. 12b will. Each echo signal then leads, as described for the error measurement on cables, at a certain point in time for a frequency practice: tuning in with the frequency of the superimposer 17 of Fig. 1 and can then in a known manner as 1, QuasiflEchosignal be recorded.

The application of the determination method is of particular interest of sediment stratifications under the sea floor. Here prepares the previously applied Impulse echo method because of the low penetration depth of short-term sound impulses great difficulties in the sediment.

As with the described invention for such measurements, however, too Low-frequency sound waves can be used, the new method leads to much more favorable measurement conditions. For this application too, as shown in Fig.

13a worked with both separate sound transmitters 78 and receivers 79 as well as with common transducers 79a according to Fig. 13b. In Figs. 13a and 13b mean, for example, sound medium 76 sea water and S0.81.82 reflection layers in the sediment of the seabed.

Claims (7)

Claims 1. Method for measuring path lengths and propagation speeds, in particular for fault measurement and location on cables, characterized in that an alternating voltage, preferably with a periodically sliding frequency, as a measurement signal is used, and that reflected at points of interference and more or less in time strongly delayed portion of this measurement signal, preferably after amplification in one selective amplifier, in a superimposed circuit when passing the frequency this superimposer with known circuits generates superimposition pulses that as "quasi" shot signals on the time axis of a cathode ray image or a other known writing device can be recorded. 2. Measuring method according to As claim 1, characterized in that the Measuring signal sliding in frequency by means of blanking or blocking circuits known per se for the measuring signal running into the measuring section to a frequency change range is limited, which is sufficient to generate an overlay pulse. 3. Measuring method according to claim 1 and 2, characterized in that the superimposed for the generation of the superimposed pulse for its part as well is made sliding in frequency. 4. Measuring method according to claim 1 to 3, characterized in that the selective amplifier has a frequency response in its gain by the measurement signal components reflected at greater distances, for which the superimposed pulse with increasing frequencies changes only at higher frequencies and with decreasing frequencies is only formed at lower levels, reinforced with a larger gain factor will. 5. Measuring method according to claim 1 to 4, characterized in that the generator producing the measurement signal and the superimposed alternating voltage The expiry of a specified time range is initially switched off and then in a selectable, relatively short time range before the frequency control starts with a start impulse to define its alternating voltage phase when starting to oscillate is opened again. 6. Measuring method according to claim 1 to 5, characterized in that the floating frequency for the superimposer to generate a superimposing pulse by frequency divider and frequency multiplier stages from the floating frequency of the hot signal generator with a fixed phase connection between the two floating frequencies is derived with a different frequency deviation. 7. Measuring method according to claim 1 to 6, characterized in that for measurements in sound media the electrical measuring signal alternating voltage with sliding Frequency into a corresponding sound wave signal with known size converters reshaped and the reflected components of the measurement signal again in a known manner received and for generating a superimposed pulse and its recording with known writing devices are used.