Option 100 Fault Location and SRL 1-3
Introduction and Measurement Theory
Fault Location Measurement Theory
Typically, fault location measurement results are expressed in one of four
ways:
Format
Select
Description
Return Loss
(RL)
The number of dB that the reflected signal is
below the incident signal. Its relationship to the
reflection coefficient (ρ) is described by the
following formula:
RL = −20 log ρ.
Reflection
Coefficient (ρ)
The ratio of the reflected voltage wave to the
incident voltage wave.
Standing
Wave Ratio
(SWR)
Any two waves traveling in opposite directions
(the incident and reflected for example) cause a
“standing wave” to be formed on the transmission
line. SWR is defined as the maximum voltage
over the minimum voltage of the standing wave.
SWR can also be mathematically derived from
the reflection coefficient (ρ) with the following
formula:
Impedance
Magnitude
The magnitude of the complex impedance at each
measurement point. See “How to Make
Impedance Measurements” on page 6-4 for
information on making impedance
measurements.
FORMAT
SWR =
1 + ρ
1 − ρ
−−−−−−−
ImpedanceMagnitude Z Z
2
real
Z
2
imaginary
+==
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