53
2) Fixed-point method
Due to the cable core along the cable twisting path forward, therefore, when on the point
of failure front the cable path forward, signal amplitude has the rule changes, according to
cable torque, when located above the failure point, generally will be the strongest signal
amplitude, and continue to move forward from the point of failure, the signal is reduced to
a stable and very small amplitude. The receiver works best in historical curve mode, and
its display will be similar to the signal amplitude curve shown above.
3) Matters needing attention:
Applicable fault resistance: Measurements with a multimeter should be close to 0, up
to 10 ohms. If it is higher than euro 10, try to burn it to low resistance first. Measuring
pointer to zero with megometer (swing meter) cannot indicate low resistance fault, it must
be measured with multimeter.
The grounding of the metal sheath of the cable must be completely unwound, and
the grounding of the zero and ground wires of the low-voltage cable should also be
unwound to avoid interference from other signals.
Before the fixed point, the path should be searched in advance and marked,
otherwise it is easy to disturb the rhythm of the rise and fall of the signal.
Note that the receiver direction should be parallel to the cable path and use the peak
detection method.
Due to the use of interphase wiring, the effective signal is very small, using high
frequency signals will be easier to detect than low frequency signals. But the residual of
high frequency signal after the fault point is also large. The frequency can be selected
according to the size of the fault resistance. If the resistance is very low, a slightly higher
frequency (e.g. 8KHz) can be selected; if the resistance is large, a low frequency can be
selected.
Start from the near end of the cable, check if there is any pitch change. If there is no
pitch change, the fault point is at the near end.
Before the fault point, there is a change of strong and weak pitch. The maximum
Summary of Contents for HZ-5000
Page 1: ...HZ 5000 Underground Cable Detector User Manual Huazheng Electric Manufacturing Baoding Co Ltd...
Page 35: ...33 Figure a Illustration of Deeper Pipes Figure b Illustration of T Branch Pipe...
Page 37: ...35 Figure e Illustration of Detection under Steel Mesh Net Illustration of Depth Measurement...
