CN108333476A - A kind of cable fault TDR localization methods and system considering cable attenuation characteristic - Google Patents
A kind of cable fault TDR localization methods and system considering cable attenuation characteristic Download PDFInfo
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Abstract
Description
技术领域technical field
本发明涉及电缆故障测试技术领域,主要涉及一种考虑电缆衰减特性的电缆故障TDR定位方法,还涉及使用该方法对电缆故障进行TDR定位的系统。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.
背景技术Background technique
电缆是供电和用电设备间连接,以及各设备间连接的枢纽,担负着电力的输送、信号的传输和分配等任务。随着电力在各种设备上的应用越来越广,电缆故障(诸如短路或断路)带来影响也越来越严重。诸如飞机上的电缆遍布于飞机各处,由于长期受到水汽、紫外线、振动、盐雾腐蚀等因素的影响,电缆容易发生短路和断路等故障。飞机电缆故障,轻则影响飞行性能,重则危及飞行安全,甚至引发飞行事故。由于飞机、舰船内电缆往往布置在狭小空间内,多不能采用传统的目视检查方法完成故障的定位。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.
目前对于飞机、舰船内电缆故障的定位,使用较为成熟的方法为TDR方法,即时域脉冲反射方法。该方法通过向电缆注入脉冲信号,脉冲信号通过电缆上阻抗不匹配点时发生反射,通过计算发射脉冲信号与反射脉冲信号之间的时间差与脉冲信号在电缆中传播速度的乘积得到故障距离,就可完成电缆故障的定位。对于飞机、舰船内电缆而言,一条电缆在布线过程中可能经过插接件、铰接点、焊接点等多种形式的阻抗变化点(即阻抗不匹配点),在该种情况下使用TDR方法进行故障定位时,除了在故障点(诸如短路或断路)形成故障反射脉冲信号外,还会在上述阻抗变化点处形成非故障反射脉冲信号,对电缆故障的定位形成较大的干扰,给出“虚警”信号,影响电缆故障定位的精度,甚至引起误判,增加维护成本。不仅如此,在使用TDR方法进行电缆故障定位时,通常使用低压的脉冲信号注入电缆进行检测,但是由于未考虑信号在电缆的实际衰减特性,只能根据经验来确定信号的发射参数(主要是指信号的电压),而缺乏理论指导,当发射参数设定较低时根本无法检出故障位置,而当发射参数设定较高时则会出现难于实现或实现成本较高的问题。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.
发明内容Contents of the invention
为了解决现有电缆故障定位存在的易发生故障误判,以及仅凭经验确定信号发射参数等问题,本发明提出了一种考虑电缆衰减特性的电缆故障TDR定位方法及系统。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.
本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法,包括如下步骤:A kind of cable fault TDR localization method of the present invention considering cable attenuation characteristic, comprises the steps:
步骤S1,根据被测电缆的特性,选定TDR发射脉冲信号的幅值Vin;所述的被测电缆的特性主要是指电缆的衰减特性,主要考虑以下影响因素:被测电缆的长度lH,被测电缆的等效电阻RL,被测电缆的特性阻抗Z0,被测电缆的等效电导GL等。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.
步骤S2,产生发射脉冲信号并注入到被测电缆中,然后采集在阻抗不匹配位置的反射脉冲信号;在TDR定位方法中,具体由脉冲信号发生器产生发射脉冲信号,并由信号采集器采集反射脉冲信号。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.
步骤S3,根据反射脉冲信号进行故障判断;具体来说,需要分析反射脉冲信号的波形,并根据反射脉冲信号和发射脉冲信号的幅值和相位关系,即可确定故障类型。但是由于受到外部环境的影响,以及经过连接器(包括插接件、铰接点、焊接点等)时产生的内部影响,可能会出现“虚警”现象,或者误判。为了提高故障判断的准确性,采用以下方法进行故障的判断: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)当反射脉冲信号幅值的绝对值|V(td)|≥1V时,则判定被测电缆存在故障,并确定故障类型和故障点距离L;根据TDR定位方法即可确定故障点距离L。(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)当0.5V≤|V(td)|<1V时,则判定被测电缆可能存在故障,然后计算可能故障点d的距离ld,其中可能故障点d的距离ld也是根据TDR定位方法确定。(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)当|V(td)|<0.5V时,则判定被测电缆不存在故障,并转至步骤S5。(3) When |V(td)|<0.5V, it is determined that there is no fault in the cable under test, and go to step S5.
步骤S4,根据电缆的衰减特性,判断可能故障点d的反射脉冲信号幅值V(td)是否合理;如果合理,则L=ld,也就说可能故障点d的距离ld即为故障点距离L;如果不合理,则可能故障点d为虚警,转至步骤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.
步骤S5,结束电缆故障定位。Step S5, end cable fault location.
优选的,步骤S4中根据电缆的衰减特性,判断可能故障点d的反射脉冲信号幅值V(td)是否合理时,具体采用如下方法: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:
步骤S41,假设被测电缆为均匀电缆,计算可能故障点d反射脉冲信号理论幅值的绝对值|V(d)|,即计算在被测电缆为均匀电缆时可能故障点d对应位置的反射脉冲信号理论幅值的绝对值|V(d)|;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)|;
步骤S42,如果|V(td)|>|V(d)|,则可能故障点d的反射脉冲信号幅值V(td)不合理;否则,则合理。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.
优选的,步骤S41中|V(d)|的计算方法具体为:Preferably, the calculation method of |V(d)| in step S41 is specifically:
其中,ld为可能故障点d的距离,RL为被测电缆的等效电阻,Z0为被测电缆的特性阻抗,GL为被测电缆的等效电导。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.
优选的,步骤S1中发射脉冲信号的幅值Vin的选定方法具体为:Preferably, the method for selecting the amplitude V in of the transmitted pulse signal in step S1 is specifically:
其中,V1(d)为被测电缆中干扰噪声的极限值,lH为被测电缆的长度;通过确定Vin,可以解决以往只能根据经验来确定信号的发射参数的问题,也避免了由此带来的各种问题。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.
优选的,V1(d)的取值为0.5V。根据大量的实验测试,对于常见的电缆而言,作用在其上的各种噪声的幅值最大为0.5V左右,此处的噪声包括外部噪声及由于连接器引入的噪声等,当发射脉冲信号经过被测电缆传播时,其幅值会逐渐衰减,当衰减至该范围时TDR定位方法将无法识别,因此选择0.5V作为判断阈值。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.
优选的,步骤S4中故障点距离L的计算方法替换为:Preferably, the calculation method of the fault point distance L in step S4 is replaced by:
其中,c为光速,εr为被测电缆绝缘材料的相对介电常数,Δt为发射脉冲信号与反射脉冲信号间的时间差。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.
为了更好地实现本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法,本发明还提出了一种使用前述TDR定位方法进行电缆故障定位的系统。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.
该定位系统,包括TDR模块、处理模块、显示模块;TDR模块用于产生发射脉冲信号,并接收反射脉冲信号;处理模块用于分析反射脉冲信号的波形,判断是否存在故障点和可能故障点d,分析可能故障点d的合理性,并确定故障类型和故障点距离L;显示模块用于显示选定参数、可能故障点d和故障点的信息;前述的显示模块、处理模块和TDR模块顺序电连接,TDR模块与被测电缆电连接。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.
优选的,定位系统中的TDR模块通过阻抗匹配接头与被测电缆电连接。通过设置阻抗匹配接头,可减少连接位置对故障定位的影响。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.
优选的,定位系统中的TDR模块由脉冲信号发生器和信号采集器组成,脉冲信号发生器用于产生发射脉冲信号,信号采集器用于采集在阻抗不匹配位置的反射脉冲信号。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.
优选的,脉冲信号发生器产生发射脉冲信号的幅值可调,从而实现前述定位方法中步骤S1的根据被测电缆的特性选定TDR发射脉冲信号的幅值Vin,减少因凭经验来确定信号的发射参数而带来的问题。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.
本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法和系统,不仅可有效去除“虚警”的影响,准确完成故障的定位;而且可根据计算结果确定发射脉冲信号的幅值Vin,彻底解决了以往因凭经验来确定信号发射参数而带来的各种问题。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.
附图说明Description of drawings
图1为考虑电缆衰减特性的电缆故障TDR定位方法流程图。Fig. 1 is a flowchart of a cable fault TDR location method considering cable attenuation characteristics.
图2为定位系统结构示意图。Figure 2 is a schematic diagram of the structure of the positioning system.
图3为TDR模块组成及TDR模块与被测电缆连接示意图。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.
图4为发射脉冲信号幅值为5.5V时测试87m处存在断路故障电缆的发射信号与反射信号波形图。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.
图5为发射脉冲信号幅值为3.3V时测试87m处存在断路故障电缆的发射信号与反射信号波形图。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.
图6为发射脉冲信号幅值为5.5V时测试100m电缆的发射信号与反射信号波形图。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.
具体实施方式Detailed ways
下面结合附图1至附图6,介绍本发明的具体实施方式。The specific implementation manner of the present invention will be introduced below in conjunction with accompanying drawings 1 to 6 .
如图1所示,本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法,主要包括五个步骤:选定发射脉冲信号的幅值,发射并采集反射脉冲信号,根据反射脉冲信号进行故障判断,判断可能故障点的合理性,结束电缆故障定位。其中判断可能故障点的合理性为可选步骤,当不存在可能故障点时,此步骤可以省略,因此在图1中用虚线表示。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 .
为了更好说明本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法,下面具体说明了本发明中是如何分析电缆衰减特性的。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.
高频脉冲信号在沿着被测电缆传播的过程中,其频率基本不发生变化;波形由于外部信号干扰和传输线路自身特性会发生畸变;信号的幅值由于介质损耗、导线损耗和辐射损耗等原因,会存在一定的衰减,而且随着信号的频率越高和传播距离越远,信号会衰减的更严重。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.
衰减是有损传输线的特性,它是求解二阶有损RLCG分布参数电路模型的直接结果。通常用αn表示单位长度的衰减,其单位为奈培/米,定义如下: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:
其中:RL为传输线的等效电阻,单位Ω;GL为传输线的等效电导,单位S;LL为传输线的等效电感,单位H;CL为传输线的等效电容,单位F;ω为传输线上信号的频率。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.
在均匀的有损传输线中,它可以表示为:In a uniform lossy transmission line, it can be expressed as:
式中:Z0为传输线的特性阻抗,单位Ω。In the formula: Z 0 is the characteristic impedance of the transmission line, the unit is Ω.
信号沿均匀电缆传播时,导线损耗对信号的影响主要是使信号幅度发生衰减。如果对于发射脉冲信号幅值为Vin的信号在传输线上传播,信号幅度随着距离的增加不是线性下降的,而是随着距离的变化呈指数下降,传输线上输入信号和输出信号幅值关系为: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:
式中,Vin表示发射脉冲信号的幅值,单位V;V(d)表示传输线上d点的电压幅值,单位V;An表示总衰减,单位奈培;ld为d点的距离,具体为信号输入端到d点的距离,单位米;αn为传输线单位长度的衰减,单位奈培/米。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.
由于分贝使用更为常见,计算更加方便,可以利用下式(4)中的转换关系,将αn转变为分贝形式: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:
由上式,得到输入电压与输出电压用分贝表示的关系:From the above formula, the relationship between the input voltage and the output voltage expressed in decibels is obtained:
由式(4)的转换关系将式(2)化为分贝的形式,则得到传输线单位长度的衰减dB/长度为: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:
由式(5)、式(6)可以知道发射信号随在传输线上衰减特性公式为:From formula (5) and formula (6), it can be known that the attenuation characteristic formula of the transmitted signal along the transmission line is:
上述为电缆衰减特性的分析过程,根据电缆衰减特性模型在给定高频脉冲信号频率和幅值的基础上得到高频脉冲信号在某一电缆上幅值与传播距离的关系。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.
下面再简述一下基于TDR(即时域脉冲反射方法)的电缆故障定位理论。TDR基本理论是传输线理论;传输线原理中将电缆作为分布参数元件,且在均匀传输线中,传输线上特性阻抗为一定值,其中电缆的特性阻抗可以由式(8)表示: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):
式中,LL1为单位长度电缆的电感,CL1为单位长度电缆的电容。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.
在传输线理论中电脉冲信号在电缆中传输的过程中,如果传输介质均匀,信号会沿着电缆一直传输,如果电缆发生故障(断路或短路),传输介质不均匀,脉冲信号会在阻抗变化的地方发生反射。传输线上阻抗不匹配处的反射系数为反射电压与发射电压之比: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:
式中,Vre为反射脉冲信号电压幅值,Zl为电缆线路障碍点的输入阻抗,Z0为电缆的特性阻抗。由(9)式可以得出以下三个特点: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)当电缆正常时,Z0=Zl,ρ=0,发射信号最终将被负载吸收而不发生反射;(1) When the cable is normal, Z 0 =Z l , ρ=0, the transmitted signal will be absorbed by the load without reflection;
(2)当电缆断路时,Zl→∞,ρ=1,此时反射的电脉冲与初始发射脉冲幅度相同,相位一致;(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)当电缆短路时,Zl→0,ρ=-1,反射的电脉冲与初始脉冲幅度相同,但相位相反。(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.
在传输线理论中,信号在传输线上是以电磁波的形式传播的;在电缆一端加上电压之后,由于其分布参数中电容的惰性,信号传递需要一定的时间。则信号在电缆中的传播速度v为: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:
式中,ε0为真空介电常数,μ0为真空磁导率,μ0=4π×10-7,εr为绝缘材料的相对介电常数,μr为绝缘材料的相对磁导率,一般为1。把ε0、μ0、μr的值代入公式(10)得: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:
式中,c为光速c=3×108;In the formula, c is the speed of light c=3×10 8 ;
由(11)式可知电缆中信号的传播速度仅仅与其绝缘材料的相对介电常数有关,与其他因素无关。信号在相同绝缘材料的电缆中具有一样的速度;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;
时域反射法通过测得发射脉冲与阻抗不匹配处的反射脉冲的时间差Δt,根据(11)式计算出信号在电缆中的传播速度来确定故障距离,故障距离为: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:
式中,L为测试端与故障点的距离,v为信号在电缆中的传播速度,Δt为发射脉冲与反射脉冲的时间差。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.
通过分析反射脉冲信号的波形,当反射脉冲信号明显时(如前所述由于电缆中的噪声水平约为0.5V,当反射脉冲信号幅值的绝对值大于等于1V时,超过噪声水平较多,认为反射脉冲信号明显),则直接判断被测电缆存在故障;当反射脉冲信号不明显时(当反射脉冲信号幅值的绝对值介于0.5V和1V之间时,认为反射脉冲信号不明显),则判断被测电缆可能存在故障,测出反射脉冲信号不明显时反射脉冲信号的幅值,然后根据发射脉冲信号与反射脉冲信号之间的时间差与脉冲信号在电缆中传播速度的乘积得到“故障距离”,最后结合电缆衰减特性计算出该位置的反射脉冲信号的理论幅值,综合判断得出故障诊断结果。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.
如图2所示,本发明的一种考虑电缆衰减特性的电缆故障TDR定位系统,包括TDR模块、处理模块、显示模块。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.
与被测电缆连接时,通过阻抗匹配接头进行连接,具体如图3所示;TDR模块中的脉冲信号发生器通过阻抗匹配接头向被测电缆发送发射脉冲信号,当被测电缆中存在阻抗不匹配位置时,反射脉冲信号通过阻抗不匹配接头由TDR的信号采集器采集。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.
实施例1:Example 1:
下面介绍一下如何使用本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法,选定发射脉冲幅值。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.
设被测电缆为一段飞机内电缆,被测电缆的特性阻抗Z0=50Ω,等效电阻RL=0.0062Ω,等效电导GL=0.00046S,被测电缆绝缘材料的相对介电常数εr=2.25,长度lh=100米,在该电缆的87米位置人为制造断路故障,分别选择两种不同幅值但频率均为100MHz的发射脉冲信号对其进行TDR定位。图4中发射脉冲信号的幅值为5.5V,图5中发射脉冲信号的幅值为3.3V。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.
如图4和图5所示,两图中均有发射脉冲信号1。但图4中存在反射脉冲信号2,根据传统的TDR定位方法,确定对应位置为故障点;而图5中不存在反射脉冲信号2。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 .
通过两图对比可知,当发射脉冲信号幅值为3.3V时,无法对故障进行定位。传统的TDR定位方法中,发射脉冲信号的幅值均是根据以往经验确定的。如前所述当选定的发射脉冲信号幅值较低时,则无法实现对故障的定义;而当选定的发射脉冲信号幅值较高时,则势必提高TDR元件的成本,当幅值过高时甚至在工程上无法实现。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.
常用来产生TDR发射脉冲信号的FPGA等芯片的工作电压是3.3V,可以通过运算放大电路将核心芯片产生的脉冲信号进行幅值放大并进行输出。对于高频脉冲信号的放大要考虑运算放大器的压摆率(压摆率是指输入为阶跃信号时闭环放大器的输出电压时间变化率的平均值,简单来说就是决定信号上升速度的一个关键指标),如果压摆率过小,生成的脉冲信号上升沿不够陡不满足TDR测试要求,压摆率大的器件价格相对昂贵。通过上述举例可知,通过选定发射脉冲信号的幅值可以帮助我们更好的设计电路,并选择相对便宜的器件,具备较大的经济价值。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.
根据本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法中的发射脉冲信号幅值选定方法可知,由确定发射脉冲信号的幅值Vin。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.
其中V1(d)为被测电缆中干扰噪声的极限值,本实施例中选择0.5V作为判断阈值V1(d)的取值,即认为信号在电缆传播过程中衰减到0.5V则认为无法识别。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.
根据上述计算方法和V1(d)的取值,计算得到Vin的幅值约为5.06V时,使用TDR技术可以对前述100米长的被测电缆进行电缆故障定位。通过该分析也可知,当Vin=3.3V时,根本无法实现电缆故障定位,因为反射脉冲信号完全淹没在噪声中。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.
实施例2:Example 2:
下面介绍一下如何使用本发明的一种考虑电缆衰减特性的电缆故障TDR定位方法及系统对电缆故障进行TDR定位的完整过程。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.
在本实施例中,被测电缆参数与实施例1完全相同,发射脉冲信号的频率为频率100MHz。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.
步骤S1,选定发射脉冲信号幅值Step S1, select the amplitude of the transmitted pulse signal
如实施例1中的计算,Vin的幅值约为5.06V时,使用TDR技术可以对前述100米长的被测电缆进行电缆故障定位。为了使得反射脉冲信号相对于噪声能够更为明显,在本实施例中适当提高Vin的幅值,具体取Vin=5.5V。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.
步骤S2,发射并采集反射脉冲信号Step S2, transmit and collect reflected pulse signal
如图6所示,发射脉冲信号1的幅值为5.5V,频率100MHz,发射脉冲信号和反射脉冲信号的时间差为Δt=500ns;信号采集器采集到的反射脉冲信号2,其幅值为V(td)=0.99V。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.
步骤S3,根据反射脉冲信号进行故障判断Step S3, perform fault judgment according to the reflected pulse signal
根据本发明的方法,由于0.5V≤|V(td)|<1V,则该点为可能故障点。According to the method of the present invention, since 0.5V≤|V(td)|<1V, this point is a possible failure point.
步骤S4,判断可能故障点的合理性Step S4, judging the rationality of possible failure points
根据计算可能故障点反射脉冲信号的理论幅值|V(d)|,通过计算得到|V(d)|=1.73V。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.
因|V(td)|<|V(d)|,因此可能故障点的反射脉冲信号幅值V(td)合理,则判断该可能故障点为故障点。进一步分析反射脉冲信号,可知该故障点的故障类型为“断路”。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".
为进一步提高故障点距离的计算精度,根据和Δt,由计算出故障点距离为L=50米,即故障点距测试端的距离为50米。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.
步骤S5,结束电缆故障定位。Step S5, end cable fault location.
最后应说明的是,以上所述仅为本发明的优选实施方式,并不用于限制本发明,尽管参照前述实施例对发明进行了详细的说明,对于本领域的技术人员来说,其依然可以对前述各实施例所记载的技术方案进行修改,或者对其中部分技术特征进行等同替换。凡在本发明的精神和原则之内,所作的任何修改、等同替换、改进等,均应包含在本发明的保护范围之内。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.
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