Description
XHGG500 completely automatic Telecom Cable Fault Locator adopts the modern microelectronic technology to develop this successful high-tech product. Combines with both pulse reflection testing and intelligent electric bridge testing for measuring the exact fault location of such as the Urban Lead cover cables, plastic cables, the broken wires of users', crossed lines, gas, bad insulation, and weak connection. It is an effective tool to reduce troubleshooting time, improve work efficiency and reduce labor intensity of line maintenance staff. It also can be used in line projects acceptance and inspection of electrical cables.
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Features
- Both pulse reflection testing and intelligent electric bridge testing can test broken lines, crossing lines, bad insulation and other types of faults.
- Automatic testing, just press the key for one time, the fault will be found.
- Manual testing function is preserved.
- English menu, easy to master and use.
- With mega meter and ohmmeter, enables to test insulation resistance and loop resistance.
- Preserve 10 testing waveforms permanently, which are cannot lost after switch off, some parts replaces the functions of printer.
- Technology of automatic gain and automatic impedance balance replaces the cumbersome potentiometer adjustment.
- Background lights display supports night operation.
- Rechargeable lithium battery, intelligent charge without duty.
- Small dimension, light weight, portable design.
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Technical Specifications
1. Pulse reflection testing:
The largest measuring range is 8 km, you can choose suitable measurement range according to the length of cable.
Testing blind spot: 0 m.
Testing resolution:
1m when it is the minimum range.
8m when it is the maximum range.
Pulse width: 80ns-10μs with automatic adjustment
Automatic impedance balance adjustment
Automatic and manual gain adjustment.
2. Intelligent electric bridge testing:
Enable to test bad insulation resistance max: 100 MΩ.
Testing accuracy:±1%×cable length
The longest cable span: 9999m.
It can be divided into three segments to input diameters: 0.3mm-0.99mm
3. Others
Rechargeable time: 4 hours
Continued operating time: 6 hours
Dimension: 230×150×160mm
Weight: 2Kg
Basic steps for cable fault testing
1. Fault nature diagnosis:
The nature of cable faults can be simply divided into the following categories:
(1)Broken wire: One or more core wires of the cable are disconnected, and the communication is interrupted. This fault is tested by the pulse method.
(2) Mixed line: It is divided into three types: grounding, self-mixing, and other mixing. It refers to the damage of the insulation layer between the core wires to the lead skin, between the same pair of core wires, and between the core wires of different pairs, and the insulation resistance drops. To a very low level (below hundreds to thousands of ohms), or even a short circuit, the communication quality is seriously affected. This kind of fault can be tested by the pulse method first, and when the waveform is difficult to identify, then use the bridge method to test.
(3) Poor insulation: the insulation material of the cable core wire is intruded by water or moisture, which reduces the insulation resistance and causes poor communication quality or even interruption. This kind of fault is similar to self-mixing, other mixing, and grounding, but the fault resistance is relatively large (above several thousand ohms), and the fault degree is relatively mild. Generally, if the insulation resistance is less than 2 megohms, it will affect the communication quality and need to be eliminated. This kind of fault cannot be detected by the pulse method generally, and needs to be tested by the bridge method instead.
After a fault occurs in the line, you should first use tools such as a measuring platform, a megohmmeter, and a multimeter to determine the fault of the line.
The nature and severity of road faults in order to select the appropriate test method.
Testers know the direction of the line and the fault situation, which is helpful to quickly determine the fault point.
After a fault occurs, comprehensively consider the time of the fault, the scope of the fault, the environment of the cable line, the location of the joint and the manhole, the influence of the weather, and possible problems. According to the measurement results, roughly judge the section of the fault.
2. Select test method:
When the fault resistance is less than several hundred to several thousand ohms, we become a low-resistance fault, otherwise it is called poor insulation
or a high-impedance fault. There is no clear boundary between high resistance and low resistance.
The pulse method is suitable for testing broken wires and low-resistance mixed wire faults. More serious poor insulation faults, there are
It can also be tested by pulse method. The operation of the pulse method is intuitive, simple, and does not require the coordination of the opposite end, so it should be used first in the test.
The bridge method can test high-resistance poor insulation faults, but it needs to find a good line, and it needs to be in
With the cooperation of the opposite end, the preparation for the test is also relatively cumbersome. The bridge method should be used after confirming that the pulse test method cannot be measured.
3. Fault location:
When testing, the intra-office equipment connected to the faulty pair should be disconnected first. Test it in the office first, make sure
Determine the minimum section of the fault point, and then go to the site for retesting to determine the exact location of the fault point.
4. Fault fixed point:
According to the results of the instrument test, compare the drawings and documents, and calibrate the specific location of the fault point. picture
When the paper information is incomplete or wrong, you can estimate the approximate location of the fault point according to the cable line conditions you have mastered, and then analyze the cause of the fault according to the fault situation and the surrounding environment until you find the fault point. For example, if there is a joint within the estimated range, it can be roughly judged that the fault point is in the joint. The farther the range, the greater the measurement error.
Pulse testing
Pulse testing is for testing broken lines and low-resistance fault.
Testing principles
Emits a pulse voltage signal to the line, when the line has faults, impedance Zi , which is input by fault point is no longer the pulse reflection that produced by characteristic impedance Zc, its reflection factor is:
ρ= (Zi-Zc)/(Zi+Zc) (1)
Reflected pulse voltage frequency value is:
Un=ρUi= [(Zi-Zc)/(Zi+Zc)] Ui (2)
From (1) we know: when the line has faults Zi→∞, ρ=1, the reflected pulse polarity is positive, as shown in Figure3a; But when the line presents short circuit trouble Zi→0, ρ=-1, the polarity of reflected pulse is negative, as shown in Figure3b, in the actual situation, the line generally has bad insulation fault, the reflection factor absolute value is smaller than 1.
Suppose the time that times from the instrument transmitted pulse, until receives the fault point reflected pulse for Δt,Δt is the come and back time that the pulse travels between the test point and the fault point. Suppose the fault distance is L, the pulse transmission velocity in electric cable velocity is V, then:
L = V Δ T / 2
Δ t is timed automatically by the instrument, and unifies the setted wave velocity V to obtain the fault distance L. In fact, in the cable transmitting process, the pulse will reflect when meets all unmatched impedance point, like the joint, the repeated joint. And display the cable characters on the screen with waveform. The user tests and judges the distance and characters of fault and unmatched point through the recognition of the starting point, the shape and the frequency of reflective pulse.
Several basic concepts
Waveform: The pulse testing depends on the waveforms to reflect cable situation, so the key of use pulse testing correctly is to understand the waveforms correctly. Because the instrument is equipped with the automatic impedance balance electric circuit, it can contract amplitude of pulse to a very small size. Basically only demonstrates the reflected pulse, is advantageous for the observation. Therefore the waveforms in Figurer 3, when test they are should be the shape the below figure .
Fault point locating: The initial station of reflected pulse waveform (the position of dashed line as shown in Figure 4) is the fault location. The most left side of the screen is the initial station of the transmitted pulse, moves the dashed line cursor to the initial station of fault reflected pulse waveform, this time the distance value that demonstrated on the screen is the fault distance. During automatic testing, the instrument can automatically move the dashed line cursor to the initial station of fault reflected pulse, but sometimes needs the manual mode to revise the position of dashed line cursor. When the dashed line cursor in other positions, the demonstrated distance value does not have the practical significance.
Range: The maximum testing distance of the instrument is 8 kilometers, and automatically sets 200 meters after switching on. What demonstrated on the screen is the cable testing waveforms in the selected range. If tests a cable of 1500 meters, you can start from minimum 200m to test, and increases the test measuring range gradually, until it can demonstrate the span of 2000 meters. The instrument automatically transforms testing range when in automatic testing.
Wave velocity: As we know, test range is actually the testing time; time multiplied by pulse transmission speed equals the distance value, so firstly we must know the exact velocity. The transmission speed of Pulse in the cable is known as velocity. From experiences, the wave velocity only related with insulation materials of the core of cables. For example, the wave velocity of plastic cable is 201 m / μ s (201 meters per microsecond). The instrument has pre-set several wave velocity values of cables in common use; the velocity can be set from choosing cables. For different manufacturers and different production technology, there may be a slight difference in velocity of the same type of cable, it can be calibrated through testing. See details in vii in this chapter.
Gain: It states the magnify times of reflective pulse. Adjusting gain on the screen can change the amplitude of the waveform. It is better to adjust the amplitude to full screen. The instrument adjusts gain when in automatic testing.
Impedance balance: The instrument interior has a resistor balancing network, make which match the characteristic impedance through adjustment to reduce the instrument transmitted pulse to the received signal influence as far as possible, stress the reflected pulse, is advantageous for the fault point judgment. The instrument will automatically adjust impedance balance during testing.
Intelligent bridge testing
The fault resistance of bad insulation is very high (above several thousand ohms), is much bigger than characteristic impedance of cable, the pulse reflection is weak, is not easy to judge the fault point. At this time it needs to carry on bridge testing. The bridge testing in this instrument has the simple megameter and the ohm meter function.
Testing principles
As we know, there are certain resistances in the cable core line, and resistance value in the unit length is same, suppose the resistance of entire core is R, if can test the core resistance from the fault to one end (test point) is Ra, and the core accurate length L is known, suppose the fault distance is La. Then:
La= (Ra/R) L
The core line resistance will be affected by temperature changes and different line diameter, but these influences are same in the cable span, use the Ra/R ratio calculation method can eliminate these influences.
During testing, firstly, the instrument calculates Ra/R automatically, and then input some data manually to calculate La. If the line diameter of the entire cable is consistent, it only need to input accurate cable length (L); If the cable is composed of cable partition with different line diameters, it need to input the partial line diameter and the partition length (see details in iii of this chapter).
This instrument adopts the intelligent electric bridge technology, the user only needs to connect lines, inputs data and the length of partial line diameter, presses several keys, the fault distance is calculated.
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