EP3797306A1 - Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmission - Google Patents
Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmissionInfo
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- EP3797306A1 EP3797306A1 EP19724835.4A EP19724835A EP3797306A1 EP 3797306 A1 EP3797306 A1 EP 3797306A1 EP 19724835 A EP19724835 A EP 19724835A EP 3797306 A1 EP3797306 A1 EP 3797306A1
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- Prior art keywords
- signal
- reflectogram
- transmission line
- exclusive
- reference signal
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/11—Locating faults in cables, transmission lines, or networks using pulse reflection methods
Definitions
- the invention relates to the field of fault analysis impacting transmission lines, such as electrical cables.
- the invention relates to the particular field of reflectometry applied to wire diagnosis which encompasses the field of detection, localization and characterization of defects in simple transmission lines or complex wire networks.
- the invention relates to a reflectometry system using binary or binarized signals for significantly reducing the complexity of implementation of such a system by reducing the calculations and the memory size used and increasing the speed of operation. execution.
- the known reflectometry methods operate according to the following method.
- a controlled reference signal for example a pulse signal or a multi-carrier signal, is injected at one end of the cable to be tested. More generally, in modern reflectometry methods, the reference signal used is chosen according to its cross-correlation properties. The signal propagates along the cable and reflects on the singularities it contains.
- a singularity in a cable corresponds to a modification of the conditions of propagation of the signal in this cable. It most often results from a fault which locally modifies the characteristic impedance of the cable by causing a discontinuity in its linear electrical parameters.
- the reflected signal is retro-propagated to the injection point and analyzed by the reflectometry system.
- the delay between the injected signal and the reflected signal makes it possible to locate one (or more) singularity (s), corresponding to an electrical fault, in the cable.
- a defect can result a short circuit, an open circuit or even a local degradation of the cable or even a simple pinching of the cable.
- the signals used by the reflectometry systems are usually generated by a programmable digital system of the processor or integrated circuit or FPGA circuit type and converted into analog signals before being injected into the cable to be analyzed. Similarly, the measured signals, analog by nature, are converted into digital signals for processing, in particular correlated with the reference signal.
- Each method uses a different reference signal with a common overall goal of obtaining good autocorrelation properties.
- the STDR method uses a pseudo-random binary signal.
- the SSTDR method combines this pseudo-random signal with a carrier frequency to shift the signal spectrum around this carrier frequency, allowing on-board and on-line use.
- MCTDR Multi Carrier Time Domain Reflectometry
- OMTDR Orthogonal MultitoneTime Domain Reflectometry
- CTDR Chos Time Domain Reflectometry
- the STDR method is for embedded use. SSTDR methods - MCTDR and OMTDR target online diagnosis.
- the OMTDR method allows the communication of several reflectometry systems during the diagnosis to improve the result by fusion of sensors.
- the CTDR method is well adapted to non-free defects and intermittent defects.
- An electronic system generates the values of the signal injected at each instant of a clock.
- This system is mostly a programmed digital system such as a processor or an FPGA.
- the digital signal is then converted to an analog signal by a digital-to-analog converter for injection into the cable.
- the signal re - transmitted by the cable is directed to an analog - to - digital converter which transmits digital values to the processing system to calculate the cross - correlation between the measured signal and the injected signal.
- a digital-to-analog converter has two parameters that significantly affect the performance of the reflectometry system. This is the resolution and sampling rate.
- the resolution corresponds to the number of bits on which each signal sample is coded. It has a particular influence on the accuracy of the inter-correlation operation.
- a weak resolution can prevent the detection of low amplitude peaks, in a reflectogram, corresponding to unprepared faults.
- the sampling frequency affects the fault location accuracy.
- a high sampling frequency makes it possible to convert the high frequency components of the signal which make it possible to locate more precisely the defaults.
- a high sampling frequency makes it possible to reduce the width of the amplitude peaks in a reflectogram and thus to discriminate neighboring peaks.
- the complexity, and therefore the cost, of a digital-to-analog converter increases with its resolution and sampling frequency.
- the invention aims to solve the limitations of current solutions by proposing a binary reflectometry system that does not require analog-digital or digital-to-analog converters.
- the subject of the invention is a reflectometry system for analyzing defects in a transmission line, a reference signal being previously generated and injected into the transmission line, the system comprising:
- a device for measuring or acquiring said analog signal retro-propagated in the transmission line
- a binarization device for quantizing said retro-propagated analog signal into a digitized signal over two quantization levels
- a correlator configured to correlate the digitized signal with the reference signal to produce a time reflectogram
- a temporal reflectogram analysis module to identify the presence of faults in the transmission line.
- the binarization device is a logic circuit of the flip-flop or comparator type.
- the reflectometry system comprises:
- An injection device for injecting the binarized reference signal into the transmission line.
- the generator and the injection device are implemented in the form of a programmable digital circuit having at least one digital output pin adapted to be connected to the transmission line.
- the reflectometry system comprises a device for adapting the impedance of the digital output pin to the impedance of the transmission line or of the printed circuit track to which it is connected.
- the reflectometry system further comprises at least one equalizer arranged between the acquisition device and a connection point between said system and the transmission line, each equalizer being configured to equalize the amplitudes obtained. on the time reflectogram for the peaks of the signal injected after its injection point in the transmission line and the signal reflected on the end of the transmission line.
- each equalizer is made by a voltage divider bridge comprising at least one resistor Rp.
- each equalizer comprises two resistors Rs, Rp arranged in a bridge of resistors.
- the values of the resistance R P or of the resistors Rs, Rp are determined from a set of impedances characterizing said system and the transmission line.
- the reference signal is a binarized pseudo-random signal.
- the correlator comprises at least one logic circuit implementing an exclusive NOR logic gate.
- the correlator comprises a counter arranged to count the number of values at 1 output from the exclusive NOR gate, the correlator being configured to calculate the cross-correlation between the digitized signal and the signal of reference from this number.
- the correlator comprises a plurality of exclusive NOR gates arranged to receive each on their inputs a sample of the digitized signal and a sample of the reference signal, an adder for summing the outputs of the logic gates NO OR exclusive , a multiplier for multiplying the output of the summator by two and an adder to add to the result of the summator a predetermined number.
- the correlator comprises at least one logic circuit implementing an exclusive OR logic gate.
- the correlator is configured to incrementally calculate a temporal reflectogram by means of the following steps:
- the correlator comprises a first shift register for receiving the reference signal, the first shift register being respectively connected to a first input of the exclusive OR logic gate and to a first input of the gate NOT OR exclusive logic, a second shift register for receiving the digitized signal, the second shift register being respectively connected to a second input of the exclusive OR logic gate and to a second input of the exclusive NOR logic gate, a register for save the results of the calculation of a temporal reflectogram, a first adder arranged to add to a current value R (i) of the temporal reflectogram, a result produced at the output of the exclusive OR logic gate and a second adder arranged to add to a value current R (i) of the temporal reflectogram, a result produced at the output of the logic gate N ON OR exclusive.
- the reflectometry system according to the invention further comprises a white noise generator arranged between the acquisition device and the binarization device.
- the reflectometry system further comprises a time differentiation or differentiation device arranged upstream of the binarization device.
- the reflectometry system according to the invention further comprises a digital time differentiation or differentiation device applied to the reference signal before it correlates with the digitized signal.
- FIG. 1 a diagram of a reflectometry system according to the prior art
- FIG. 1a an example of a reflectogram obtained with the reflectometry system of FIG. 1,
- FIG. 2 a diagram of a reflectometry system according to a first embodiment of the invention
- FIG. 3 two diagrams illustrating an operation of binarization of a digital signal
- FIG. 4 two diagrams illustrating a reflectogram obtained respectively with a reflectometry system of the prior art and a reflectometry system according to the first embodiment of the invention
- FIG. 5 a diagram of a correlator according to a first embodiment of the invention
- FIG. 6 is a flowchart detailing the steps for implementing an optimized calculation method of a reflectogram
- FIG. 7 a diagram illustrating a comparison of the signal injected at a point of a cable and of the signal measured at a point of a cable at two successive instants
- FIG. 8 a diagram of a correlator according to a second variant embodiment of the invention.
- FIG. 9 a diagram of a reflectometry system according to a second embodiment of the invention.
- FIG. 10 two diagrams illustrating a reflectogram obtained respectively with a reflectometry system of the prior art and a reflectometry system according to the second embodiment of the invention
- FIG. 11 a diagram of a reflectometry system according to a third embodiment of the invention.
- FIG. 12 a diagram of an example of a differentiator circuit
- FIG. 13 two diagrams illustrating a reflectogram obtained respectively with a reflectometry system of the prior art and a reflectometry system according to the third embodiment of the invention
- FIG. 14 two temporal reflectograms illustrating a problem solved by a fourth embodiment of the invention.
- FIG. 15 a diagram of a reflectometry system according to a fourth embodiment of the invention.
- FIG. 16 a diagram of an example of an equalizer device
- FIG. 17 a diagram illustrating the determination of the values of the resistances of an equalizer device according to a variant of the fourth embodiment of the invention.
- FIG. 18 two temporal reflectograms illustrating the results obtained thanks to the fourth embodiment of the invention.
- FIG. 1 represents a diagram of a fault analysis system 100 in a transmission line L, such as a cable, according to a usual method of time domain reflectometry of the state of the art.
- a transmission line L such as a cable
- Such a system mainly comprises a generator GEN of a digital reference signal.
- the generated digital reference signal is converted analogically via a digital-to-analog converter DAC and then injected at a point on the transmission line L by means of a directional coupler CPL or any other device for injecting a signal into a line.
- the signal propagates along the line and reflects on the singularities it contains. In the absence of a fault on the line, the signal is reflected on the end of the line if the termination of the line is not adapted.
- the signal In the presence of a fault on the line, the signal is reflected on the impedance discontinuity caused by the fault.
- the reflected signal is back-propagated to a measurement point, which may be common at the injection point or different.
- the retro-propagated signal is captured via the directional coupler CPL and then digitally converted by an ADC digital analog converter. COR correlation is then performed between the digital signal thus obtained and a copy of the digital signal generated before injection to produce a time reflectogram R (t) corresponding to the inter-correlation between the two signals.
- the DF position of a fault on the cable L ie its distance to the signal injection point, can be directly obtained from the measurement, on the calculated time reflectogram R (t), the duration t DF between the first amplitude peak recorded on the reflectogram and the amplitude peak corresponding to the signature of the defect, thanks to the knowledge of a speed value of signal propagation in the line.
- FIG. 1a shows an example of a reflectogram R (n) obtained with the aid of the system of FIG. 1, on which a first peak of amplitude is observed at an abscissa N and a second peak of amplitude at an abscissa N + M.
- the first amplitude peak corresponds to the reflection of the signal at the point in the cable, while the second peak corresponds to the reflection of the signal on an impedance discontinuity caused by a fault.
- the abscissa point N is generally taken as a time reference and is reduced to the abscissa 0 by subtraction of N.
- an optional average MOY calculation can be performed before or after COR correlation. The two locations of the average calculation are equivalent from an arithmetic point of view.
- An analysis device (not shown in FIG. 1) is responsible for analyzing the reflectogram R (t) in order to deduce presence and / or fault location information as well as any electrical characteristics of the defects.
- the transmission and reception parts of the system described in FIG. 1 can be implemented in the same device or in two separate devices.
- the transmitting part of the system comprises the signal generator, the digital-to-analog converter and the signal injection device in a cable.
- the reception part of the system comprises the device for measuring the back-propagated signal in the cable and the numerical calculation modules comprising the calculation of average and inter-correlation.
- FIG. 2 describes a reflectometry system according to a first embodiment of the invention.
- the system 200 comprises a generator GEN of the reference signal used.
- the generator GEN is able to directly generate a binary signal, for example a pseudo-random signal of the CTDR type.
- the generator GEN is able to generate a digital signal quantized over several bits and furthermore comprises a binarization element of the generated digital signal. Binarization is a process of transforming the digital signal into a series of binary values taking the values 0 or 1 or taking the values -1 or 1. The binarization is performed so that any positive or zero value of the signal is transformed into a value equal to 1 and any negative value of the signal is transformed into a value equal to -1.
- the generator GEN is, for example, implemented in the form of a programmable digital system, such as a processor or a reconfigurable circuit of the FPGA type.
- the generator GEN comprises at least one digital output pin to which is connected a CPL coupler (or any other equivalent means) capable of injecting the binary output signal of the GEN generator into the cable L.
- the generated binary signal is output to the digital output pin in the form of an analog signal for which the binary value 1 is outputted by a maximum voltage VCC and the binary value 0 (or -1) is delivered by a minimum voltage - VDC.
- the GEN generator digital pin is capable of delivering VCC and -VCC voltages.
- an impedance matching device is positioned between the output pin of the generator and the coupler CPL to adapt the output impedance of the generator to that of the cable L.
- an additional component or circuit is disposed downstream of the output pin.
- This component is, for example, a Schmitt flip-flop whose The high and low thresholds are set to a voltage equal to a value between 0 and the maximum voltage VCC, for example VCC / 2, and the power levels are set to the maximum voltage values VCC and minimum - VCC.
- the additional circuit is composed of a transformer whose main comprises N turns and the secondary comprises 2N turns and a capacitor disposed upstream of the main.
- the additional circuit is composed of a logic inverter between the voltages VCC and -VCC and two resistors arranged as a voltage divider between the minimum voltage - VCC and the digital input of the circuit.
- the additional component must include a device for adapting its input impedance to the impedance of the digital output pin of the generator.
- Figure 3 shows respectively a chaotic pseudo-random signal as generated (in the upper diagram) and the same signal after the binarization operation (bottom diagram).
- the back-propagated signal in the L-cable is captured, i.e., acquired or measured, by means of the CPL coupler (which may be the same or different from the coupler used for the signal injection) or any other means of measurement or signal acquisition.
- This signal is analog.
- the binarization operation can be done either directly by the used digital component COR, by connecting a digital input of the component (possibly equipped with an impedance matching system) to the coupler CPL, or by means of a component or additional circuit inserted between the CPL coupler and the digital component COR.
- This circuit is a threshold-type thresholding device, or comparator B, which makes it possible to convert the measured analog signal into a digital signal. binary.
- the COR correlator then performs the cross-correlation calculation between the received signal and the signal injected into the cable.
- the system according to the invention as described in FIG. 2 does not require an analog digital converter or a digital-to-analog converter.
- This type of component is expensive, consumes a lot of energy and its use limits the speed of signal acquisition.
- the higher the speed of acquisition or conversion of the analog signal to a digital signal the higher the number of samples per second, which gives better results for fault detection but entails a higher cost for the detection of a fault. component.
- the necessary memory size is also decreased.
- the number of bits used to sample an analog signal is generally greater than 8 bits, which generates a very large necessary storage capacity.
- a single bit per sample is necessary, which makes it possible to reduce the memory size by a factor of at least 8. Lossless digital compression methods would make it possible to further improve this gain in memory.
- the signal acquisition frequency is increased thanks to the invention since it is no longer limited to the sampling frequency of the analog-digital converter.
- the signal acquisition frequency for the system described in FIG. 2 is that of the thresholding device B which is close to or equal to the frequency of the digital component GEN.
- Another advantage of the invention is that, despite the loss of information in the measured signal due to the decrease in the number of quantization bits, the reflectogram resulting from the inter-correlation calculation of the signal measured and the signal generated, is comparable to that which would be obtained with a method according to the prior art as shown in Figure 4.
- FIG. 4 shows two reflectograms obtained for a line of length equal to 20 meters comprising four non-free defects of regularly spaced increasing amplitudes.
- the top diagram corresponds to a reflectogram obtained with a system according to the prior art comprising a digital to analog converter and an analog digital converter.
- the diagram on the left corresponds to a reflectogram obtained with a system according to the invention.
- the defects are correctly identifiable by peaks of equivalent amplitudes on the two diagrams.
- FIG. 5 represents a diagram of an example of COR correlator according to one embodiment of the invention.
- the intercorrelation at a given instant represented by an index i can be expressed in the following form:
- the products S (k) S c (j) can be calculated using a logic gate "NO OR exclusive" also called XNOR and the index value i of Cross-correlation product can be calculated by summing the outputs of the XNOR function bit by bit.
- Another way to achieve this sum is to count the number of times that the respective bits of the signals S c and S are equal (that is, where the output of the function XNOR is equal to 1).
- Card (E) designates the number of elements of a set E and the sets E ,, E., are defined by:
- the COR correlator can be made from one or more XNOR logic gate (s).
- Each XNOR logic gate receives the respective signals S and S c on its two inputs.
- the outputs of the logic gates XNOR are summed by means of a summator SOM.
- the summator SOM can be replaced by a counter able to count the number of 1 at the output of the logic gates XNOR, this number corresponding to the number of values of the set E ,.
- the result produced at the output of the summator SOM is shifted one bit to the left in order to perform a multiplication by two.
- An adder ADD is then used to add to this result the term K-i + 1.
- the COR correlator finally comprises a BUF register for saving the values of the reflectogram R thus calculated.
- the correlator described in FIG. 5 can be arranged differently to fulfill the same function.
- it may include a single XNOR logic gate and a counter instead of the SOM summator.
- the multiplication operation by 2 can also be performed using a multiplier.
- the COR correlator described in FIG. 5 operates with binary signal samples taking the values 0 or 1.
- the correlator thus designed makes it possible to perform an intercorrelation calculation more simply and more quickly because it does not require any multiplication or Fourier transform.
- the patent application FR1662396 relates to a method for calculating a reflectogram to better distribute the number of operations to be implemented in order to make the calculation more efficient.
- FIG. 6 schematizes the main steps of the method of calculating a reflectogram as described in the patent application FR1662396.
- the method begins with an initialization step 300 which comprises the following substeps:
- the initialization step 300 may also be made optional.
- the reflectogram R 0 is initialized to 0, then the following steps of the method are directly executed. It is then necessary to wait to have measured K samples of the signal propagated in the cable to obtain a complete reflectogram in favor of a saving in computing time from the start of the process.
- the number K is a parameter of the method and corresponds to the length (in number of samples) of the cross correlation made between the reference signal and the measured signal to calculate the reflectogram.
- the signal measurement can be performed simultaneously with the injection of the signal into the cable or can be performed with an initial time offset.
- the measuring device comprises a reference signal generator whose function is to generate a copy of the reference signal injected into the signal injection device. the cable by the injection device. This copy is used to calculate the reflectogram.
- the initialization step 300 produces a first reflectogram, initial, denoted R 0 .
- the two steps 301, 302 of the method consist in generating and injecting 301 in the cable, iteratively, dK samples of the reference signal and then measuring 302 dK samples of the signal propagated in the cable.
- the number dK is a parameter of the invention and is preferably chosen much lower than the value of K.
- the last K samples of the injected signal and the last K samples of the measured signal are saved in a buffer or a local memory in order to perform an intercorrelation calculation over a duration corresponding to the last K samples. It is recalled that the value of dK is assumed to be much lower than the value K. It is assumed that the measured signal has been previously digitized to preserve digital samples.
- FIG. 7 illustrates a representation of the buffer containing the last K samples of the reference signal on the one hand and the signal measured on the other hand, at two successive instants i and i + dK. Between these two successive instants, a number of new signal samples are injected into the cable and the same number of new signal samples are measured.
- the dK samples of the oldest buffer S c (denoted ECH-A in FIG. 7) are deleted from the buffer S c , i + dK at the instant following i + dK.
- the K-dK samples of the buffer S cj the most recent (denoted ECH-C in Figure 7) are shifted in the buffer S c , i + dK at the next time i + dK.
- the buffer S c , i + dK contains new samples (denoted ECH-N in FIG. 7) at the instant i + dK.
- FIG. 7 shows that at two successive instants i and i + dK, the buffer containing the K last samples of the reference signal has K-dK identical values. Similarly, at two successive instants i and i + dK, the buffer containing the last K samples of the measured signal also has K-dK identical values.
- a value Ri (n) of the reflectogram R, at time i corresponds to the inter-correlation between the samples of the buffer S c containing the last K samples of the reference signal and the samples of the buffer S, containing the last K samples the measured signal. This calculation is given by relation (2) below.
- the index n varies over the set of time values for which the reflectogram R, is calculated.
- the relation (2) thus gives a value of the reflectogram R, for a time instant of index n.
- index n varies from 1 to K.
- the index value n of the reflectogram R, calculated at time i, can be decomposed into two sums, from relation (2) which becomes the relation
- the reflectogram values at a time i + dK are determined from the reflectogram values at a time i preceding in step 303 of the method.
- Step 303 thus consists in subtracting from the previous reflectogram Ri the correlation products between the dK samples of the signal measured at the instant before i and a number dK of corresponding samples of the reference signal injected into the transmission line at the yet i, and to add the previous reflectogram R, the correlation products between dK new samples measured at the current time i + dK dK and a number of corresponding samples of the reference signal injected into the transmission line the current moment i + dK.
- the calculation of the current reflectogram made in step 303 comprises a number of operations to be performed substantially reduced. A minimum number of operations is reached for a value of dK equal to 1 sample.
- Steps 301, 302, 303 are iterated for a duration corresponding to the cable scan time.
- Step 303 is executed for all the values of a reflectogram.
- the calculation explained in relation (5) is executed in parallel for n values of a reflectogram, corresponding to n successive time indices.
- a particular embodiment of the invention relates to the case where the number dK of injected samples then measured at each instant i is equal to 1. This scenario is the one for which the number of operations required for each iteration to calculate a reflectogram , is the weakest.
- the step 303 of calculating the reflectogram can be simplified from equation (5) as follows.
- the method for calculating a reflectogram described above can be further optimized, according to the invention, to reduce the number of operations to be performed.
- adding the product S (K) * S c (K + 1 -n) corresponds, for binary signals, to add the result of a NON OR exclusive operation or XNOR to the values S (K) and S c ( K + 1-n).
- this method of incremental calculation of the reflectogram can be implemented, for binary signals, only from logic gates XOR and XNOR.
- FIG. 8 represents a diagram of a COR correlator according to a second variant embodiment of the invention, this correlator implementing the aforementioned incremental calculation.
- a COR correlator comprises at least one XOR logic gate and one XNOR logic gate as well as two BUF I , BUF 2 shift registers.
- the first shift register BUFi is able to receive the samples of the binary signal S generated by the component GEN.
- the second shift register BUF 2 is able to receive the samples of the signal S c binary obtained at the output of the thresholding device B.
- the correlator COR also comprises two adders ADD-i, ADD 2 and a third register BUF 3 to save the values R (i) calculated from the reflectogram.
- the logic gate XOR and the first adder ADD-i are configured to add to the current value R (i) the result of the exclusive OR operation applied to the samples S (n) and S c (1).
- the logic gate XNOR and the second adder ADD 2 are configured to add to the current value R (i) the result of the exclusive NO OR operation applied to the samples S (K) and S (K + 1 -n).
- the samples of the binary signals S and S c take the values +1 or -1.
- the samples are shifted from the two shift registers S and S c , the new sample of the reference signal injected is recorded in the shift register S c and the new sample of the signal in the shift register S c measured.
- the shift operation can be suppressed by implementing a technique similar to that of the circular registers, in which the index of the oldest samples replaced by the samples measured at the current time is incremented or decremented in a circular manner (modulo the size of the register).
- the invention applies to any type of reflectometry signals but more particularly to pseudo-random signals such as the CTDR chaotic signals. Indeed, the pseudo-random character of these signals makes it possible not to degrade the quality of the inter-correlation of the signal measured with the signal injected when the signal is binary or binarized.
- This advantage is important in the field of the detection and location of defects on a cable because the identification of defects is related to the identification of amplitude peaks in the result of inter-correlation.
- FIG. 9 describes a second embodiment of a reflectometry system according to the invention.
- the system of FIG. 9 comprises the same elements as that described in FIG. 2 but also comprises a generator 901 of analog white noise, arranged between the coupler CPL and the device for binarization B of the analog signal.
- the analog white noise generated by the generator 901 is, for example, a Gaussian additive white noise. It is added to the analog signal measured by the PLC coupler.
- An advantage of the system described in FIG. 9 is that the addition of white noise to the measured analog signal makes it possible to better highlight, on the final reflectogram, the peaks of low amplitude corresponding to non-free defects. Indeed, low amplitude peaks can sometimes be masked by peaks near higher amplitude.
- the addition of white noise makes it possible, on average, to highlight these peaks of low amplitude.
- the amplitude of the added white noise is preferably at least equal to the average amplitude of the signal.
- the amplitude of the white noise added is of the order of two to three times larger than the average amplitude of the signal.
- FIG. 10 represents two reflectograms obtained for a line of length equal to 20 meters including a non-straightforward defect of low amplitude in the middle of the cable.
- the diagram on the left corresponds to a reflectogram obtained with a system according to the prior art comprising a digital-analog converter and an analog-digital converter.
- the diagram on the right corresponds to a reflectogram obtained with a system according to the second embodiment described in FIG. 9.
- FIG. 11 describes a third embodiment of a reflectometry system according to the invention.
- the system of FIG. 11 comprises the same elements as the system described in FIG. 2 but furthermore comprises a differentiating or differentiating circuit 902 disposed between the output of the cable and the binarization device B.
- a derivation circuit is configured to perform a time derivative operation of the analog signal measured by the coupler CPL.
- a differentiator circuit is configured to determine the difference between the value of the signal at a time t and its value at a previous instant t-1.
- the addition of a time derivation or differentiation operation before the binarization operation also makes it possible to better highlight the amplitude peaks in the final reflectogram.
- the amplitude peaks are bipolar as is identified in FIG. 13.
- FIG. 13 represents two reflectograms obtained for a line of length equal to 20 meters including a non-straightforward defect of low amplitude in the middle of the cable.
- the top diagram corresponds to a reflectogram obtained with a system according to the prior art comprising a digital to analog converter and an analog digital converter.
- the bottom diagram corresponds to a reflectogram obtained with a system according to the third embodiment described in FIG. 11.
- the system of Figure 1 1 may or may not include a white noise generator 901 disposed upstream of the circuit 902.
- FIG. 12 schematizes an example of a derivation circuit 902 capable of performing a time derivative operation.
- Such a circuit 902 comprises two capacitors Ci, C 2 and three resistors R I , R 2 , R 3 arranged in the manner shown in FIG. 12. It also comprises a ground GND and a power supply VCC. Moreover, it comprises a comparator COMP whose output S is directly connected to the circuit implementing the binarization operation. The input of the circuit 902 is directly connected to the cable L via a CPL coupler (not shown in FIG. 12).
- the circuit 902 may be implemented by any other implementation that makes it possible to perform a time derivative function or time differentiation of an analog signal, for example by means of a sample-and-hold device and an analog memory.
- a time derivative operation or temporal differentiation is applied to the generated binary signal before carrying out the intercorrelation with the binarized signal at the output of the binarization device B.
- This operation may be carried out by the correlator COR or by a digital circuit 903 capable of calculating the derivative or the difference term in terms of the output signal of the generator GEN inserted between the generator GEN and the correlator COR.
- the circuit 903 and COR correlator are, by example, implemented on a single integrated circuit or FPGA circuit.
- This variant has the particular advantage of obtaining monopolar amplitude peaks in the reflectogram, and no longer bipolar as is the case if the derivation or differentiation operation is applied only to the measured signal.
- FIG. 14 represents, on a temporal diagram, two examples of reflectograms obtained for a cable of length equal to 30 meters and presenting a non-surface imperfection at 15 meters. It is assumed that the amplitude of the first peak corresponding to the injection point of the signal and the amplitude of the last peak corresponding to the end of the cable are equal.
- the first refi reflectogram is obtained with a system according to the invention.
- the second Reflectogram Ref 2 is obtained with a system according to the prior art for which the measured signal is not binarized.
- the amplitude of the peak of the reflectogram corresponding to the non-frank defect located at 15 meters is of the order of 0.1. It can be seen that this peak is embedded in the secondary lobes of the Ref 2 reflectogram in the case where the measured signal is not binarized. It is therefore not possible to detect this peak reliably with a system according to the prior art.
- the peak corresponding to the non-straightforward defect is amplified.
- This phenomenon is related to the binarization of the measured signal. Indeed, the reflected signal values close to 0 are amplified to values +1 or -1 after binarization.
- the signal injected into the cable is reflected at the end of the cable that is assumed for the moment without flaws.
- the retro-propagated signal that is measured can be considered as the sum of the signal injected and the same signal delayed by a delay equal to the round trip time of the signal between the injection point and the measuring point through the end of the cable.
- the injected signal is binary, it takes the values 1 or -1.
- the signal measured after backpropagation takes the values 2, -2 or 0 (omitting, for the sake of simplicity, the amplification or attenuation due to the mismatch at the injection point and the termination of the cable). In fact, the measured signal takes the value 0 in about 50% of cases.
- this phenomenon strongly depends on the equality of the amplitudes of the signal transmitted after the injection point and the signal reflected at the end of the cable. More generally, it is observed that it is possible to detect a non-straightforward defect which generates a reflection of the amplitude signal greater than or equal to the difference of the amplitudes of the signal transmitted after the injection point and the signal reflected at the end of the signal. cable. In other words, the closer these two amplitudes are, the more it is possible to detect non-straightforward faults generating small amplitudes in the reflectectogram calculated after correlation.
- Figure 15 describes a fourth embodiment of a reflectometry system according to the invention.
- the system of FIG. 15 comprises the same elements as the system described in FIG. 11 (the elements 901, 902, 903 are optional) but also comprises an equalizer 904 configured to equalize the amplitudes of the signal transmitted after the injection point of the cable and signal reflected at the end of the cable.
- FIG. 16 schematizes an exemplary embodiment of the equalizer 904. It consists of a voltage divider bridge or resistor bridge comprising two resistors Rp and Rs arranged upstream of the connection of the reflectometry system to the cable.
- the equalizer 904 is a quadripole which is connected on the one hand to the cable and on the other hand directly to the tracks of the printed circuit on which the system according to the invention is implemented.
- FIG. 16 diagrammatically shows the emission part E of the system which essentially comprises the generator GEN and a track or impedance connection Zi which connects this part of the system to the cable.
- the reception part R of the system essentially comprises the binarization device B and the correlator COR.
- the cable has a characteristic impedance Z c .
- the load at the end of the cable has an impedance Z L and the reception part R of the system has an impedance Z R.
- Impedances Zi, Z 2 and Z R are system manufacturing parameters. The impedances Z c and Z L depend on the cable to be tested.
- the values of the resistors Rp and Rs are determined so as to equalize the amplitudes of the signal at the injection point and at the point of reflection. In a variant, the resistor R s is suppressed.
- the values of the resistances Rp and Rs are determined empirically, with charts or automatically. They depend on the cable parameters (impedance, attenuation, dispersion, propagation speed) and are controllable.
- the values of the resistances R P and R s can be determined empirically by means of the following relationships. It is assumed later that the signal injection point and the signal measurement point are identical. Firstly, it is possible to determine the amplitude A of the signal at the injection point (called “amplitude of the injection peak”) on the one hand and the amplitude B of the signal reflected on the charge at the end of the cable (called “End-of-cable peak amplitude”) from the following relationships:
- Ti is the transmission coefficient of the signal, at the injection point, between the generator and the cable,
- T R is the signal transmission coefficient, at the injection / measurement point, between the generator and the reception part R of the system,
- T 2 is the transmission coefficient of the back-propagated signal, at the point of injection, of the cable towards the reception part R of the system,
- R R is the reflection coefficient of the signal on the reception part R of the system
- RL is the reflection coefficient of the signal on the load at the end of the cable
- R 0 is the reflection coefficient of the signal from the reception part R of the system, on the measurement point.
- Z R is the impedance of the reception part R of the system
- Zi is the impedance of the track which connects the emission part E of the system to the equalizer 904,
- Z 2 is the impedance of the track which connects the reception part R of the system to the equalizer 904,
- Y P , R PI and R P2 are intermediate variables which depend on coefficients A ps , B pS , C ps , D pS , which themselves depend on the resistors R s and R p of the equalizer 904.
- the condition so that the amplitudes A and B are equal is given by the relation:
- FIG. 17 illustrates, in a diagram, an example of a method for determining the values of the resistors R s and R p of the equalizer 904 from graphs.
- the curve 910 represents the value of the resistance Rp as a function of the impedance Z c of the cable, considering that the cable is terminated by a short circuit.
- the curve 91 1 represents the value of the resistor Rs as a function of the impedance Z c of the cable.
- Curve 912 represents the equal value of the amplitudes of the two peaks as a function of the cable impedance Z c .
- Tolerance ranges can be considered around the optimal values of the resistances R s and R p in order to widen the strict equality of the amplitudes of the two peaks with minimal differences between the two amplitudes. These tolerance ranges are in particular determined according to the minimum amplitude of a peak corresponding to a non-straightforward defect that one wishes to be able to detect.
- FIG 18 illustrates the results obtained with the fourth embodiment of the invention.
- Reflectogram 920 is obtained without equalizer 904 and has two peaks of different amplitudes.
- the resistors of the equalizer 904 are programmable in order to adapt the system to the type of cable tested.
- the values of the resistances R s and R p can also be obtained automatically, in a calibration phase of the system, by measuring the amplitudes of the two peaks of the reflectogram and by adjusting the values of the resistors as and when measured according to a closed-loop operation .
- the determination of the values of the resistances R s and R p can also be done semi-analytically by empirically calculating a range of values possible for the resistors R s and R p according to the parameters of the system and then adjusting these values by analysis of the reflectogram.
- the voltage divider bridge can be replaced by any equivalent device capable of performing the same equalization function.
- the equalizer (s) may also be arranged between the tracks of the printed circuit connecting the transmission line to the injection or measuring device.
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Resistance Or Impedance (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Tests Of Electronic Circuits (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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FR1854285A FR3081561B1 (fr) | 2018-05-23 | 2018-05-23 | Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmission |
FR1856741A FR3081562B1 (fr) | 2018-05-23 | 2018-07-20 | Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmission |
PCT/EP2019/062919 WO2019224137A1 (fr) | 2018-05-23 | 2019-05-20 | Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmission |
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EP3797306A1 true EP3797306A1 (fr) | 2021-03-31 |
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EP19724835.4A Withdrawn EP3797306A1 (fr) | 2018-05-23 | 2019-05-20 | Systeme de reflectometrie binaire pour l'analyse de defauts dans une ligne de transmission |
Country Status (3)
Country | Link |
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US (1) | US11531052B2 (fr) |
EP (1) | EP3797306A1 (fr) |
FR (2) | FR3081561B1 (fr) |
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CN114859180B (zh) * | 2022-05-30 | 2024-06-25 | 海南电网有限责任公司乐东供电局 | 一种基于连续波的电缆故障双端定位方法 |
Family Cites Families (11)
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US5425017A (en) * | 1993-01-11 | 1995-06-13 | Forte Networks, Inc | Token ring local area network testing apparatus inserted in an active "T" co |
US5382910A (en) * | 1993-04-06 | 1995-01-17 | John Fluke Mfg. Co., Inc. | Dual time base zero dead zone time domain reflectometer |
TW559668B (en) * | 1999-02-08 | 2003-11-01 | Advantest Corp | Apparatus for and method of measuring a jitter |
US6934655B2 (en) * | 2001-03-16 | 2005-08-23 | Mindspeed Technologies, Inc. | Method and apparatus for transmission line analysis |
WO2004046652A2 (fr) * | 2002-11-19 | 2004-06-03 | University Of Utah | Dispositif et procede de detection d'anomalies dans un cable |
US8280655B2 (en) * | 2007-03-01 | 2012-10-02 | International Rectifier Corporation | Digital power monitoring circuit and system |
US8988081B2 (en) * | 2011-11-01 | 2015-03-24 | Teradyne, Inc. | Determining propagation delay |
FR2994484B1 (fr) * | 2012-08-07 | 2014-08-22 | Commissariat Energie Atomique | Systeme de reflectometrie comprenant un mecanisme de transmission d'informations |
FR3003410B1 (fr) * | 2013-03-18 | 2016-07-01 | Win Ms | Dispositif de protection de reseaux electriques |
FR3037147B1 (fr) * | 2015-06-04 | 2017-06-02 | Win Ms | Procede et dispositif de reflectometrie pour le diagnostic de cables en fonctionnement. |
FR3060129B1 (fr) | 2016-12-14 | 2020-06-19 | Commissariat A L'energie Atomique Et Aux Energies Alternatives | Procede de calcul d'un reflectogramme pour l'analyse de defauts dans une ligne de transmission |
-
2018
- 2018-05-23 FR FR1854285A patent/FR3081561B1/fr not_active Expired - Fee Related
- 2018-07-20 FR FR1856741A patent/FR3081562B1/fr active Active
-
2019
- 2019-05-20 US US17/055,975 patent/US11531052B2/en active Active
- 2019-05-20 EP EP19724835.4A patent/EP3797306A1/fr not_active Withdrawn
Also Published As
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FR3081562A1 (fr) | 2019-11-29 |
US20210255230A1 (en) | 2021-08-19 |
FR3081561B1 (fr) | 2020-06-12 |
FR3081561A1 (fr) | 2019-11-29 |
FR3081562B1 (fr) | 2020-06-12 |
US11531052B2 (en) | 2022-12-20 |
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