CN108333476A - A kind of cable fault TDR localization methods and system considering cable attenuation characteristic - Google Patents

Abstract

Considering that the cable fault TDR localization methods of cable attenuation characteristic and system, localization method include the following steps the invention discloses a kind of：Selected transmitting pulse signal amplitude, emits and acquires reflected impulse signal, carries out breakdown judge according to reflected impulse signal, judges the reasonability of possible breakdown point, terminates cable fault positioning；System using this method includes display module, processing module and TDR modules.Using the localization method and system, the influence of " false-alarm " is not only can effectively avoid, the accurate positioning for completing failure；And the amplitude of transmitting pulse signal can be determined according to result of calculation, it thoroughly solves the problems, such as to bring due to determining signal emission parameter because by rule of thumb in the past various.

Description

A cable fault TDR location method and system considering cable attenuation characteristics

technical field

The invention relates to the technical field of cable fault testing, mainly relates to a cable fault TDR positioning method considering the cable attenuation characteristics, and also relates to a system for TDR positioning of cable faults using the method.

Background technique

The cable is the hub of the connection between power supply and electric equipment, as well as the connection between various equipment, and is responsible for the transmission of power, transmission and distribution of signals and other tasks. As electricity is used more and more widely in various devices, the impact of cable failures (such as short circuits or open circuits) has become more and more serious. For example, the cables on the aircraft are all over the aircraft. Due to the long-term influence of water vapor, ultraviolet rays, vibration, salt spray corrosion and other factors, the cables are prone to short circuit and open circuit failures. Aircraft cable faults can affect flight performance in the slightest, endanger flight safety in severe cases, and even cause flight accidents. Since the cables in aircraft and ships are often arranged in a narrow space, traditional visual inspection methods cannot be used to complete fault location.

At present, for the location of cable faults in aircraft and ships, the more mature method is the TDR method, which is the instant domain pulse reflection method. In this method, a pulse signal is injected into the cable, and the pulse signal is reflected when it passes through an impedance mismatch point on the cable, and the fault distance is obtained by calculating the product of the time difference between the transmitted pulse signal and the reflected pulse signal and the propagation speed of the pulse signal in the cable. The location of the cable fault can be completed. For cables in aircraft and ships, a cable may pass through various forms of impedance change points (ie, impedance mismatch points) such as connectors, hinge points, and welding points during the wiring process. In this case, TDR is used When the method is used for fault location, in addition to forming a fault reflected pulse signal at the fault point (such as a short circuit or an open circuit), a non-fault reflected pulse signal will also be formed at the above-mentioned impedance change point, which will greatly interfere with the location of the cable fault and give A "false alarm" signal will affect the accuracy of cable fault location, and even cause misjudgment and increase maintenance costs. Not only that, when using the TDR method for cable fault location, a low-voltage pulse signal is usually injected into the cable for detection, but because the actual attenuation characteristics of the signal in the cable are not considered, the transmission parameters of the signal can only be determined based on experience (mainly refers to Signal voltage), but lack of theoretical guidance, when the transmission parameters are set low, the fault location cannot be detected at all, and when the transmission parameters are set high, it will be difficult to implement or the implementation cost is high.

Contents of the invention

In order to solve the existing problems of easy fault misjudgment and determination of signal transmission parameters based on experience in existing cable fault location, the present invention proposes a cable fault TDR location method and system considering cable attenuation characteristics.

A kind of cable fault TDR localization method of the present invention considering cable attenuation characteristic, comprises the steps:

Step S1, according to the characteristics of the cable under test, select the amplitude V _in of the TDR emission pulse signal; the characteristics of the cable under test mainly refer to the attenuation characteristics of the cable, mainly considering the following influencing factors: the length l of the cable under test _H , the equivalent resistance _RL of the tested cable, the characteristic impedance Z ₀ of the tested cable, the equivalent conductance _GL of the tested cable, etc.

Step S2, generate a transmission pulse signal and inject it into the cable under test, and then collect the reflected pulse signal at the position where the impedance does not match; in the TDR positioning method, the transmission pulse signal is generated by the pulse signal generator and collected by the signal collector reflected pulse signal.

Step S3, perform fault judgment according to the reflected pulse signal; specifically, it is necessary to analyze the waveform of the reflected pulse signal, and determine the fault type according to the amplitude and phase relationship between the reflected pulse signal and the transmitted pulse signal. However, due to the influence of the external environment and the internal influence generated when passing through the connector (including connectors, hinge points, welding points, etc.), "false alarm" phenomenon or misjudgment may occur. In order to improve the accuracy of fault judgment, the following methods are used for fault judgment:

(1) When the absolute value of the reflected pulse signal amplitude |V(td)|≥1V, it is determined that there is a fault in the cable under test, and the fault type and the distance L of the fault point are determined; the distance of the fault point can be determined according to the TDR positioning method L.

(2) When 0.5V≤|V(td)|<1V, it is determined that there may be a fault in the cable under test, and then calculate the distance l _d of the possible fault point d, where the distance l _d of the possible fault point d is also located according to TDR The method is determined.

(3) When |V(td)|<0.5V, it is determined that there is no fault in the cable under test, and go to step S5.

Step S4, according to the attenuation characteristics of the cable, judge whether the reflected pulse signal amplitude V(td) of the possible fault point d is reasonable; if it is reasonable, then L= _ld , that is to say, the distance l _d of the possible fault point d is the fault point distance L; if it is unreasonable, it is possible that fault point d is a false alarm, and go to step S5.

Step S5, end cable fault location.

Preferably, in step S4, according to the attenuation characteristics of the cable, when judging whether the reflected pulse signal amplitude V(td) of the possible fault point d is reasonable, the following method is specifically adopted:

Step S41, assuming that the cable under test is a uniform cable, calculate the absolute value |V(d)| of the theoretical amplitude of the reflected pulse signal at the possible fault point d, that is, calculate the reflection at the corresponding position of the possible fault point d when the cable under test is a uniform cable The absolute value of the theoretical amplitude of the pulse signal |V(d)|;

In step S42, if |V(td)|>|V(d)|, the amplitude V(td) of the reflected pulse signal at fault point d may be unreasonable; otherwise, it is reasonable.

Preferably, the calculation method of |V(d)| in step S41 is specifically:

Among them, l _d is the distance of the possible fault point d, _RL is the equivalent resistance of the tested cable, Z ₀ is the characteristic impedance of the tested cable, and _GL is the equivalent conductance of the tested cable.

Preferably, the method for selecting the amplitude V _in of the transmitted pulse signal in step S1 is specifically:

Among them, V ₁ (d) is the limit value of the interference noise in the cable under test, and l _H is the length of the cable under test; by determining V _in , the problem that the transmission parameters of the signal can only be determined based on experience in the past can be solved, and it can also avoid various problems arising from this.

Preferably, the value of V ₁ (d) is 0.5V. According to a large number of experimental tests, for common cables, the maximum amplitude of various noises acting on it is about 0.5V. The noise here includes external noise and noise introduced by the connector. When the pulse signal is transmitted When propagating through the tested cable, its amplitude will gradually attenuate. When the attenuation reaches this range, the TDR positioning method will not be able to identify it. Therefore, 0.5V is selected as the judgment threshold.

Preferably, the calculation method of the fault point distance L in step S4 is replaced by:

in, c is the speed of light, ε _r is the relative permittivity of the cable insulation material under test, and Δt is the time difference between the transmitted pulse signal and the reflected pulse signal.

In order to better realize a cable fault TDR location method of the present invention considering cable attenuation characteristics, the present invention also proposes a system for cable fault location using the aforementioned TDR location method.

The positioning system includes a TDR module, a processing module, and a display module; the TDR module is used to generate a transmitted pulse signal and receive a reflected pulse signal; the processing module is used to analyze the waveform of the reflected pulse signal to determine whether there is a fault point and a possible fault point d , analyze the rationality of the possible fault point d, and determine the fault type and fault point distance L; the display module is used to display the selected parameters, possible fault point d and fault point information; the aforementioned display module, processing module and TDR module sequence Electrically connected, the TDR module is electrically connected to the cable under test.

Preferably, the TDR module in the positioning system is electrically connected to the cable under test through an impedance matching joint. By setting the impedance matching joint, the influence of the connection position on the fault location can be reduced.

Preferably, the TDR module in the positioning system is composed of a pulse signal generator and a signal collector, the pulse signal generator is used to generate the transmitted pulse signal, and the signal collector is used to collect the reflected pulse signal at the position where the impedance does not match.

Preferably, the pulse signal generator generates an adjustable amplitude of the transmitted pulse signal, thereby realizing the amplitude V _in of the selected TDR transmitted pulse signal according to the characteristics of the cable under test in step S1 of the aforementioned positioning method, and reducing the frequency due to empirical determination. The problem caused by the transmission parameters of the signal.

A cable fault TDR positioning method and system considering the cable attenuation characteristics of the present invention can not only effectively remove the influence of "false alarm" and accurately complete fault positioning; but also determine the amplitude V _in of the transmitted pulse signal according to the calculation results, It completely solves various problems caused by determining the signal transmission parameters by experience in the past.

Description of drawings

Fig. 1 is a flowchart of a cable fault TDR location method considering cable attenuation characteristics.

Figure 2 is a schematic diagram of the structure of the positioning system.

Figure 3 is a schematic diagram of the composition of the TDR module and the connection between the TDR module and the cable under test.

Figure 4 is the waveform diagram of the transmitted signal and reflected signal when the amplitude of the transmitted pulse signal is 5.5V, and there is an open circuit fault cable at 87m.

Fig. 5 is a waveform diagram of the transmitted signal and the reflected signal when the transmitted pulse signal amplitude is 3.3V and there is an open circuit fault cable at 87m.

Figure 6 is a waveform diagram of the transmitted signal and reflected signal when the transmitted pulse signal amplitude is 5.5V when testing a 100m cable.

Detailed ways

The specific implementation manner of the present invention will be introduced below in conjunction with accompanying drawings 1 to 6 .

As shown in Figure 1, a cable fault TDR location method of the present invention considering the cable attenuation characteristics mainly includes five steps: select the amplitude of the transmitted pulse signal, transmit and collect the reflected pulse signal, and perform fault detection according to the reflected pulse signal Judgment, judge the rationality of possible fault points, and end the cable fault location. Among them, judging the rationality of the possible fault point is an optional step. When there is no possible fault point, this step can be omitted, so it is represented by a dotted line in Fig. 1 .

In order to better illustrate a cable fault TDR location method of the present invention considering the cable attenuation characteristics, how to analyze the cable attenuation characteristics in the present invention is specifically described below.

During the propagation of the high-frequency pulse signal along the cable under test, its frequency basically does not change; the waveform will be distorted due to external signal interference and the characteristics of the transmission line itself; the amplitude of the signal is due to dielectric loss, wire loss and radiation loss, etc. The reason is that there will be a certain attenuation, and as the frequency of the signal is higher and the distance of propagation is longer, the signal will be attenuated more seriously.

Attenuation is a characteristic of lossy transmission lines, which is a direct result of solving a second-order lossy RLCG distributed parameter circuit model. Usually _αn is used to represent the attenuation per unit length, and its unit is Neper/meter, which is defined as follows:

Among them: R _L is the equivalent resistance of the transmission line, the unit is Ω; G _L is the equivalent conductance of the transmission line, the unit is S; L _L is the equivalent inductance of the transmission line, the unit is H; C _L is the equivalent capacitance of the transmission line, the unit is F; ω is the frequency of the signal on the transmission line.

In a uniform lossy transmission line, it can be expressed as:

In the formula: Z ₀ is the characteristic impedance of the transmission line, the unit is Ω.

When a signal propagates along a uniform cable, the effect of wire loss on the signal is mainly to attenuate the signal amplitude. If the signal with the amplitude of the transmitted pulse signal V _in propagates on the transmission line, the signal amplitude does not decrease linearly with the increase of distance, but decreases exponentially with the change of distance, the relationship between the input signal and output signal amplitude on the transmission line for:

In the formula, V _in represents the amplitude of the transmitted pulse signal, unit V; V(d) represents the voltage amplitude at point d on the transmission line, unit V; A _n represents the total attenuation, unit Neper; l _d is the distance of point d , specifically the distance from the signal input terminal to point d, in meters; α _n is the attenuation per unit length of the transmission line, in Neper/meter.

Since the use of decibels is more common and the calculation is more convenient, the conversion relationship in the following formula (4) can be used to convert α _n into decibels:

From the above formula, the relationship between the input voltage and the output voltage expressed in decibels is obtained:

Converting formula (2) into decibel form by the conversion relationship of formula (4), then the attenuation dB/length per unit length of the transmission line is obtained as:

From formula (5) and formula (6), it can be known that the attenuation characteristic formula of the transmitted signal along the transmission line is:

The above is the analysis process of the cable attenuation characteristics. According to the cable attenuation characteristic model and given the frequency and amplitude of the high-frequency pulse signal, the relationship between the amplitude and the propagation distance of the high-frequency pulse signal on a certain cable is obtained.

The cable fault location theory based on TDR (time-domain pulse reflection method) will be briefly described below. The basic theory of TDR is the transmission line theory; in the transmission line theory, the cable is used as a distributed parameter element, and in a uniform transmission line, the characteristic impedance of the transmission line is a certain value, and the characteristic impedance of the cable can be expressed by formula (8):

In the formula, L _L1 is the inductance of the cable per unit length, and C _L1 is the capacitance of the cable per unit length.

In the transmission line theory, when the electric pulse signal is transmitted in the cable, if the transmission medium is uniform, the signal will be transmitted along the cable. If the cable fails (open circuit or short circuit), the transmission medium is uneven, and the pulse signal will be in the impedance change Where reflections occur. The reflection coefficient at an impedance mismatch on a transmission line is the ratio of the reflected voltage to the emitted voltage:

In the formula, V _re is the voltage amplitude of the reflected pulse signal, Z _l is the input impedance of the obstacle point of the cable line, and Z ₀ is the characteristic impedance of the cable. The following three characteristics can be obtained from formula (9):

(1) When the cable is normal, Z ₀ =Z _l , ρ=0, the transmitted signal will be absorbed by the load without reflection;

(2) When the cable is disconnected, Z _l → ∞, ρ = 1, at this time the reflected electric pulse has the same amplitude and phase as the initial transmitted pulse;

(3) When the cable is short-circuited, Z _l → 0, ρ = -1, the reflected electric pulse has the same amplitude as the initial pulse, but the phase is opposite.

In the transmission line theory, the signal propagates in the form of electromagnetic waves on the transmission line; after the voltage is applied to one end of the cable, due to the inertia of the capacitance in its distribution parameters, the signal transmission takes a certain amount of time. Then the propagation velocity v of the signal in the cable is:

where _ε0 is the vacuum permittivity, μ ₀ is the vacuum magnetic permeability, μ ₀ =4π×10 ^-7 , ε _r is the relative permittivity of the insulating material, and μ _r is the relative magnetic permeability of the insulating material, which is generally 1. Substituting the values of ε ₀ , μ ₀ , and μ _r into formula (10), we get:

In the formula, c is the speed of light c=3×10 ⁸ ;

It can be known from (11) that the propagation speed of the signal in the cable is only related to the relative dielectric constant of its insulating material, and has nothing to do with other factors. Signals have the same speed in cables of the same insulation material;

The time domain reflection method measures the time difference Δt of the reflected pulse at the place where the transmitted pulse does not match the impedance, and calculates the propagation speed of the signal in the cable according to (11) to determine the fault distance. The fault distance is:

In the formula, L is the distance between the test end and the fault point, v is the propagation speed of the signal in the cable, and Δt is the time difference between the transmitted pulse and the reflected pulse.

By analyzing the waveform of the reflected pulse signal, when the reflected pulse signal is obvious (as mentioned earlier, because the noise level in the cable is about 0.5V, when the absolute value of the reflected pulse signal amplitude is greater than or equal to 1V, the noise level is exceeded. If the reflected pulse signal is considered obvious), it is directly judged that there is a fault in the cable under test; when the reflected pulse signal is not obvious (when the absolute value of the reflected pulse signal amplitude is between 0.5V and 1V, the reflected pulse signal is considered not obvious) , it is judged that there may be a fault in the cable under test, and the amplitude of the reflected pulse signal is measured when the reflected pulse signal is not obvious, and then according to the product of the time difference between the transmitted pulse signal and the reflected pulse signal and the propagation speed of the pulse signal in the cable, " Fault distance", and finally calculate the theoretical amplitude of the reflected pulse signal at this position in combination with the cable attenuation characteristics, and comprehensively judge to obtain the fault diagnosis result.

As shown in FIG. 2 , a cable fault TDR location system considering cable attenuation characteristics of the present invention includes a TDR module, a processing module, and a display module.

When connecting to the cable under test, connect it through the impedance matching connector, as shown in Figure 3; the pulse signal generator in the TDR module sends a pulse signal to the cable under test through the impedance matching connector. When the position is matched, the reflected pulse signal is collected by the TDR signal collector through the impedance mismatched joint.

Example 1:

The following describes how to use a cable fault TDR location method considering the cable attenuation characteristics of the present invention to select the transmit pulse amplitude.

Assuming that the cable under test is a section of the cable inside the aircraft, the characteristic impedance of the cable under test Z ₀ =50Ω, the equivalent resistance R _L =0.0062Ω, the equivalent conductance G _L =0.00046S, the relative permittivity of the cable insulation material ε _r = 2.25, length l _h = 100 meters, artificially create an open-circuit fault at the 87-meter position of the cable, and select two different amplitude but 100MHz transmitting pulse signals for TDR positioning. The amplitude of the transmitted pulse signal in Fig. 4 is 5.5V, and the amplitude of the transmitted pulse signal in Fig. 5 is 3.3V.

As shown in FIG. 4 and FIG. 5 , there is a transmit pulse signal 1 in both figures. However, there is a reflected pulse signal 2 in Figure 4, and the corresponding location is determined to be the fault point according to the traditional TDR positioning method; while there is no reflected pulse signal 2 in Figure 5 .

By comparing the two figures, it can be seen that when the amplitude of the transmitted pulse signal is 3.3V, the fault cannot be located. In the traditional TDR positioning method, the amplitude of the transmitted pulse signal is determined based on past experience. As mentioned earlier, when the amplitude of the selected transmission pulse signal is low, the definition of the fault cannot be realized; and when the amplitude of the selected transmission pulse signal is high, the cost of the TDR component is bound to be increased. When the amplitude Too high is not even possible engineering.

The operating voltage of FPGA and other chips commonly used to generate TDR transmission pulse signals is 3.3V, and the pulse signal generated by the core chip can be amplified and output through an operational amplifier circuit. For the amplification of high-frequency pulse signals, the slew rate of the operational amplifier should be considered (the slew rate refers to the average value of the time change rate of the output voltage of the closed-loop amplifier when the input is a step signal, which is simply a key to determine the rising speed of the signal Index), if the slew rate is too small, the rising edge of the generated pulse signal is not steep enough to meet the TDR test requirements, and the device with a high slew rate is relatively expensive. From the above examples, we can know that selecting the amplitude of the transmitted pulse signal can help us better design the circuit, and choose relatively cheap devices, which have greater economic value.

According to the method for selecting the amplitude of the transmitted pulse signal in a cable fault TDR location method considering cable attenuation characteristics of the present invention, it can be known that by Determine the amplitude V _in of the transmitted pulse signal.

Wherein V ₁ (d) is the limit value of interference noise in the cable under test, in this embodiment, 0.5V is selected as the value of the judgment threshold V ₁ (d), that is, it is considered that the signal is attenuated to 0.5V during the cable propagation process. not recognized.

According to the above calculation method and the value of V ₁ (d), when the amplitude of _Vin is calculated to be about 5.06V, the TDR technology can be used to locate the cable fault of the aforementioned 100-meter-long cable under test. It can also be seen from this analysis that when V _in =3.3V, cable fault location cannot be realized at all, because the reflected pulse signal is completely submerged in noise.

Example 2:

The following describes how to use a cable fault TDR locating method and system in the present invention considering cable attenuation characteristics to perform a complete process of TDR locating cable faults.

In this embodiment, the parameters of the cable under test are exactly the same as those in Embodiment 1, and the frequency of the transmitted pulse signal is 100 MHz.

Step S1, select the amplitude of the transmitted pulse signal

As calculated in Embodiment 1, when the amplitude of _Vin is about 5.06V, the TDR technique can be used to locate the cable fault of the aforementioned 100-meter-long cable under test. In order to make the reflected pulse signal more obvious than the noise, in this embodiment, the amplitude of _Vin is appropriately increased, specifically, _Vin =5.5V.

Step S2, transmit and collect reflected pulse signal

As shown in Figure 6, the amplitude of the transmitted pulse signal 1 is 5.5V, the frequency is 100MHz, and the time difference between the transmitted pulse signal and the reflected pulse signal is Δt=500ns; the reflected pulse signal 2 collected by the signal collector has an amplitude of V (td) = 0.99V.

Step S3, perform fault judgment according to the reflected pulse signal

According to the method of the present invention, since 0.5V≤|V(td)|<1V, this point is a possible failure point.

Step S4, judging the rationality of possible failure points

according to Calculate the theoretical amplitude |V(d)| of the reflected pulse signal at the possible fault point, and get |V(d)|=1.73V through calculation.

Since |V(td)|<|V(d)|, the reflected pulse signal amplitude V(td) of the possible fault point is reasonable, and the possible fault point is judged as the fault point. Further analysis of the reflected pulse signal shows that the fault type of this fault point is "open circuit".

In order to further improve the calculation accuracy of the fault point distance, according to and Δt, given by Calculate the fault point distance as L=50 meters, that is, the distance between the fault point and the test end is 50 meters.

Step S5, end cable fault location.

Finally, it should be noted that the above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the invention has been described in detail with reference to the foregoing examples, it is still possible for those skilled in the art The technical solutions recorded in the foregoing embodiments are modified, or some of the technical features are equivalently replaced. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A cable fault TDR positioning method considering cable attenuation characteristics is characterized by comprising the following steps:

step S1, according to the characteristic of the tested cable, selecting the amplitude V of the TDR emission pulse signal_in；

Step S2, generating a transmitting pulse signal, injecting the transmitting pulse signal into the tested cable, and then collecting a reflected pulse signal at the position where the impedance is not matched;

step S3, judging the fault according to the reflected pulse signal;

when the absolute value | V (td) | of the amplitude of the reflected pulse signal is more than or equal to 1V, judging that the tested cable has a fault, and determining the fault type and the fault point distance L;

when the absolute value of 0.5V is less than or equal to absolute value V (td) is less than 1V, the possibility of fault of the tested cable is judged, and then the distance l of a possible fault point d is calculated_d；

When | V (td) | < 0.5V, it is determined that there is no fault in the measured cable, and go to step S5;

step S4, judging whether the amplitude V (td) of the reflected pulse signal of the possible fault point d is reasonable or not according to the attenuation characteristic of the cable; if reasonable, L ═ L_d(ii) a If not, the possible fault point d is a false alarm, and the step S5 is executed;

and step S5, ending the cable fault location.

2. The TDR localization method of cable fault considering cable attenuation characteristic according to claim 1, wherein in step S4, when determining whether the amplitude v (td) of the reflected pulse signal at the possible fault point d is reasonable according to the attenuation characteristic of the cable, the following method is adopted:

step S41, assuming that the cable to be tested is a uniform cable, calculating the absolute value | V (d) | of the theoretical amplitude of the reflected pulse signal of the possible fault point d;

step S42, if | V (td) | > | V (d) |, the amplitude V (td) of the reflected pulse signal at the possible fault point d is not reasonable; otherwise, it is reasonable.

3. The TDR locating method for cable fault considering the attenuation characteristic of the cable according to claim 2, wherein the calculation method of | v (d) | in step S41 is specifically:

wherein l_dDistance of possible fault points d, R_LIs the equivalent resistance, Z, of the cable under test₀Is the characteristic impedance of the cable to be tested, G_LIs the equivalent conductance of the cable under test.

4. The TDR positioning method for cable faults considering cable attenuation characteristics as claimed in any one of claims 1 to 3, wherein the amplitude V of the transmitted pulse signal in step S1_inThe selection method specifically comprises the following steps:

wherein, V₁(d) Limit value of interference noise in tested cable,/_HIs the length of the cable to be tested.

5. The TDR positioning method for cable faults considering the attenuation characteristics of cables as claimed in claim 4, wherein V₁(d) Is 0.5V.

6. The TDR localization method of cable fault considering attenuation characteristic of cable according to claim 1, wherein the calculation method of fault point distance L in step S4 is replaced by:

wherein,c is the speed of light, ε_rAnd delta t is the time difference between the transmitted pulse signal and the reflected pulse signal, which is the relative dielectric constant of the insulating material of the tested cable.

7. A system for cable fault location using the TDR location method of any one of claims 1 to 6, comprising a TDR module, a processing module, a display module;

the TDR module is used for generating a transmitting pulse signal and receiving a reflected pulse signal;

the processing module is used for analyzing the waveform of the reflected pulse signal, judging whether a fault point and a possible fault point d exist or not, analyzing the rationality of the possible fault point d, and determining the fault type and the fault point distance L;

the display module is used for displaying the selected parameters, the possible fault points d and the information of the fault points;

the display module, the processing module and the TDR module are electrically connected in sequence, and the TDR module is electrically connected with a tested cable.

8. The TDR locating system for cable faults considering attenuation characteristics of the cable as claimed in claim 7, wherein the TDR module is electrically connected to the cable to be tested through an impedance matching connector.

9. The TDR locating system for cable faults considering the attenuation characteristics of the cable as claimed in claim 7 or 8, wherein the TDR module is composed of a pulse signal generator for generating the transmission pulse signal and a signal collector for collecting the reflection pulse signal at the impedance mismatch position.

10. The TDR locating system for cable faults considering the attenuation characteristics of the cable as claimed in claim 9, wherein the amplitude of the pulse signal generated by the pulse signal generator is adjustable.