RU2009516C1 - Method of determining place of damage in cable metal envelope - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: signal being modulated by low-frequency signal on carrier frequency is used for exciting electromagnetic field along path of the cable. Shift of signal phase is measured in the beginning of tested section of cable line on matched load of the circuit within cable envelope relatively the same signal in the circuit "envelope-earth". Tested cable is influenced by external directed radiation electromagnetic signal. Place of influence of directed radiation signal is shifted along cable in the direction from its end to its beginning. Then phase shift is measured and place of damage is detected in relation to position of directed radiation signal effect place. At this signal measured phase shift starts to change monotonically. EFFECT: improved precision of measurement. 1 dwg

Description

 The invention relates to measuring equipment and can be used, for example, to determine the location of damage to the metal sheath of communication cables.

 A known method for determining the location of cable damage (1), which includes generating electromagnetic field pulses in the cable and registering at one end of the cable the moment of arrival of the front of the pulse reflected from the location of the damage, while the test cable is externally affected by a directional radiation pulse, sequentially moves along the cable in the direction from the end of the cable, on which the induced pulses are recorded, at the same end of the cable, the instant of arrival of the direct-guided pulse is recorded, having detected etsya fault location by location point of impact momentum directed radiation, in which is recorded at the tail end coincidence points joining edges pryamonavedennogo and reflected pulses of electromagnetic field. However, this method cannot be used to determine the location of damage to the metal sheath of the cable.

, где Δφ- сдвиг фазы сигнала с частотой модуляции на ближнем конце для цепи внутри оболочки кабеля относительно этого же сигнала на ближнем конце направляющей структуры;
F - частота модуляции;
v₁ и v₂ - соответственно фазовые скорости направляющей структуры и цепи внутри оболочки кабеля.There is a method of determining the location of damage to the metal sheath of the cable (2), which consists in creating an electromagnetic field along the cable path by supplying alternating current to the guide structure formed by the cable sheath and ground, while alternating current is supplied at the carrier frequency corresponding to the minimum sheath coupling resistance, modulated low-frequency signal, measure the phase shift of the signal with the modulation frequency at the matched load of the near end of the circuit inside the cable sheath relative to this e signal at the near end of the guide structure, and the distance to the place of damage is determined by the formula
l ₁ =

where Δφ is the phase shift of the signal with the modulation frequency at the near end for the circuit inside the cable sheath relative to the same signal at the near end of the guide structure;
F is the modulation frequency;
v ₁ and v ₂ are the phase velocities of the guide structure and the circuit inside the cable sheath, respectively.

The disadvantage of this method is the low accuracy of determining the location of cable damage due to the large error that occurs when counting the distance l ₁ from the proximal end of the cable, as well as errors in the estimates of Δφ, F, v ₁ and v ₂ .

 The purpose of the invention is to increase the accuracy of determining the location of damage.

 This goal is achieved by the fact that the method of determining the place of damage to the metal sheath of the cable is that, by a signal at the carrier frequency, a modulated low-frequency signal, an electromagnetic field is excited along the cable path and the phase shift of the signal with the modulation frequency at the matched load of the circuit is measured at the beginning of the cable section under study inside the cable sheath with respect to the same signal in the sheath-ground circuit, while the test cable is externally affected by an electromagnetic signal directed emission were impact point signal directional radiation sequentially moved along the cable from the end of the test portion in a direction toward its top, which produces the measurement phase shift, and detect the fault location in terms of location feedback signal directed radiation, in which the measured phase shift starts monotonously change.

A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that the test cable is externally affected by an electromagnetic signal of directional radiation, the point of influence of the signal of directional radiation is moved along the cable and the location of the damage is determined by the location of the point of influence at which the measured phase shift begins to monotonously change. Due to this, there is no need to determine and count from the beginning of the investigated section of the distance l ₁ . As a result, the error arising in counting the distance l ₁ and the error in estimating the value of l _{1 are} eliminated. This provides a higher accuracy of determining the location of damage to the cable sheath in comparison with the known method, which is the prototype.

 Thus, the proposed method meets the criteria of the invention of "novelty." In the study of other well-known technical solutions in this technical field, the features that distinguish the invention from the known, were not identified and therefore they provide the claimed technical solution according to the criterion of "significant differences".

 The drawing shows a functional diagram of a device that implements this method.

 The device comprises a high-frequency modulated signal generator with a highly directional antenna 1, a test cable, the metal sheath 2 of which is damaged, with an insulated conductor 3, a phase meter 4.

 The method for determining the location of cable damage is as follows.

-

, где v₂, v₁ - скорости распространения электромагнитной энергии в цепи оболочка-земля и цепи жила-оболочка, соответственно;
F - частота модуляции.When the test cable is subjected to directional electromagnetic radiation generated by the generator 1, the signal induced in the circuit propagates in this circuit from the point of influence (point B) to the beginning of the test section where phase shift measurements are made (point A). In the place of damage to the metal sheath (point B), the signal penetrates from the external circuit into the internal one and the insulated conductor 3 — cable sheath 2 — to the beginning of the test section (point A) propagates along the circuit. If the point of impact (point B) is located at a distance from the beginning of the investigated area greater than the distance to the damage site - l ₁ , then the phase shift of the signals measured in the sheath-ground circuit and the core-sheath circuit measured by a phase meter 4
Δφ = 2ΠFl

-

where v ₂ , v ₁ - the propagation velocity of electromagnetic energy in the shell-ground circuit and the core-sheath chain, respectively;
F is the modulation frequency.

 Obviously, the measured phase shift when moving the point of influence (point B) from the end of the investigated area to the place of damage to the shell (point B) is a constant value.

l

-

-

, где Х - расстояние между точками В и Б.If the impact point (point B) is located between the place of damage (point B) and the beginning of the test area (point A), where the phase shift is measured, then the phase shift measured by the phase meter 4 is equal to
Δφ = 2ΠF

l

-

-

where X is the distance between points B and B.

 Thus, when the point of impact (point B) is moved from the place of damage (point B) to the beginning of the test site (point A), the measured phase shift will monotonically change, proportional to the distance X.

 An operator with a directional emitter moves along the cable route from the end of the investigated section towards its beginning until the result of the measurement of the phase shift begins to change monotonously.

 It should be noted that, in contrast to the known method, with this method there is no need to measure the distance to the place of damage, and then count this distance along the cable from the beginning of the studied section of the cable line, which leads to higher accuracy in determining the location of damage to the cable sheath. (56) Copyright certificate of the USSR N 632966, cl. G 01 R 31/08, 1978.

 USSR author's certificate N 1379751, cl. G 01 R 31/08, 1988.

Claims (1)

 METHOD FOR DETERMINING THE DAMAGE OF THE METAL CABLE OF THE CABLE, consisting in the fact that the signal at the carrier frequency, modulated by a low-frequency signal, excites an electromagnetic field along the cable path and measure the phase shift of the signal with the modulation frequency at the matched frequency of the cable line inside the cable sheath relative to this the signal in the sheath - ground circuit, characterized in that the test cable is externally affected by an electromagnetic signal of directional radiation, then ku directional radiation exposure signal sequentially moved along the cable from the end of the test portion in a direction toward its top, which produces the phase shift measurement and detect the fault location in terms of location feedback signal directed radiation, in which the measured phase shift starts monotonously change.

Images