TDR-based anti-interference cable fault testing system and testing method

Abstract

The invention relates to the technical field of cable fault testing, and particularly relates to a TDR-based anti-interference cable fault testing system. The TDR-based anti-interference cable fault testing system is characterized by comprising a master control module for controlling the system to work, a pulse generation module for sending a single pulse signal to a tested cable, a pulse time interval measurement module for measuring a pulse time interval, a D / A converter for providing comparison reference voltage and a comparator for filtering an echo. The invention further relates to a testing method. The method comprises the steps of (1) providing the comparison reference voltage to the comparator; (2) transmitting the single pulse signal to the tested cable; (3) judging whether a first reflected wave is screened out or not, if not, adjusting the comparison reference voltage and repeating the previous steps until the first reflected wave is screened out; and (5) measuring the time interval between the reflected wave and the first reflected wave and completing measurement. The testing system and the testing method have the beneficial effects that a measurement interference signal can be effectively filtered and a first reflected pulse is accurately determined, thereby quickly determining a cable fault position.

Description

technical field [0001] The invention relates to the technical field of cable fault testing, in particular to a TDR-based anti-interference cable fault testing system and a testing method using the system. Background technique [0002] The time domain reflectometry (TDR) is used to calibrate the location of the fault point by reflecting the low-voltage high-speed pulse and measuring the time difference between the transmitted pulse and the reflected pulse at the fault point. The attenuation of the reflected pulse varies with the length and material of the line. The attenuation is large, which requires signal amplification of the reflected pulse. The usual method is to use high-speed A / D acquisition waveform to realize fault point judgment. This method not only has high cost and complex circuit implementation, but also has low measurement accuracy. The first reason is that a cable may pass through Multiple impedance transformation points such as connectors, hinge points, weld...

AI Technical Summary

Problems solved by technology

The usual method is to judge the fault point through high-speed A / D acquisition waveform. This method not only has high cost and complex circuit implementation, but also has low measurement accuracy. The first reason is that a cable may pass through during the wiring process. Multiple impedance transformation points such as connectors, hinge points, welding points, etc., when a single pulse signal is input to the cable, in addition to forming an obvious reflected pulse at the fault point (such as an open circuit or a short circuit) (in order to be consistent with the echo The difference is also called the first reflected wave), and an echo will be formed at the impedance transformation point of the cable. Although its amplitude is smaller than that of the first reflected wave, it still forms a large interference when measuring the reflection time; the second reason Yes, the first reflected wave will produce multiple reflections to form multiple echoes, and the echo amplitude is gradually attenuated, but it is also a kind of interference wave

The basic characteristic of the interference wave formed by the above two situations is that the amplitude will be smaller than the first reflected wave, but it is difficult to determine which pulse is the first reflected wave that can really represent the distance to the fault point by using the pulse time interval measurement circuit, which makes the measurement results There is uncertainty

[0003] Especially in some weak current fields with complex wiring, such as control cables in aircraft and ships, the length of the cable itself is limited, and the input pulse, first reflected wave, and various echoes are sometimes intertwined, making it substantially difficult to use time domain reflection Effectively determine the point of failure

[0004] In addition, in order not to cause damage to the weak current system and to be able to distinguish the short-length cable fault point, a low-voltage narrow pulse is usually used as the input wave. Because the pulse width is narrow, the reflected wave waveform is complex, the amplitude is variable, and it is very irregular. , which also brings difficulties to the measurement time, so it also needs to be changed into a more regular pulse

[0005] Of course, there may also be other external interferences in the measurement environment. These interference signals are usually clearly different from the low-voltage narrow pulses used to detect cable faults in terms of pulse form, pulse width, etc., and are sporadic, so they are easy to judge and filter However, the above-mentioned echo interference signal fundamentally restricts the application of time domain reflectometry in cable fault measurement

Since the interference of multiple echoes cannot be filtered, the current TDR-based cable fault test system basically needs to display the waveform through an oscilloscope-like display device, and then measure the time by manually moving the marking line. This operation is difficult to achieve automatic judgment, and the efficiency low

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