8
Fault Mapper Pro
®
Model CA7027
CHAPTER 4
OPERATION
4.1
Principles of Operation
The Fault Mapper Pro
®
works by measuring the time taken for a signal to
travel to the far end of the cable under test, or to an intermediate fault and
return. The velocity at which the signal travels Vp (Velocity of Propagation)
will depend on the characteristics of the cable.
Based on the selected Vp and the measured travel time of the test pulse,
the Fault Mapper Pro
®
calculates and displays impedance anomalies and
their distances along the cable.
4.2
Accuracy and Velocity of Propagation (Vp)
The Fault Mapper Pro
®
measures distances to faults and cable lengths to
an accuracy of ±1%. This measurement accuracy is based upon the cor
-
rect value of Vp being used for the cable under test, and homogeneity of
the Vp along the cable length.
If the Vp is set incorrectly by the operator, or the Vp varies along the length
of the cable, then additional errors will be incurred and the measurement
accuracy will be affected.
See § 4.8 for setting the Vp.
NOTE:
The Vp is less well defined with unshielded multi-conductor cable,
including power cable, and is lower when a cable is tightly wound on a drum
than when it is installed in a linear fashion.
Correct measurement of fault distances is also dependent on the cursor being
positioned accurately by the operator.
When locating faults with the Fault
Mapper Pro
®
the cursor should be positioned at the beginning of the feature on
the cable waveform as shown below.
Vp=72% Z=100
Ω
621ft
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