User Guide

4.1 Setting an NVP Value
34
The HiTester employs the TDR (time domain reflectometry)
method to measure the amount of time from the input of a pulse
to the return of its reflected wave from the far end of the cable.
Length is calculated by the following formula:
L : Cable length (m)
C : Speed of light in a vacuum = 3
× 10
8
(m/s)
T : Pulse propagation time from insertion to reflection return (s)
NVP : Nominal Velocity of Propagation (the speed of a signal through a
cable relative to the speed of light in a vacuum.)
Cable length measurement accuracy is ± 4% rdg. ± m, where
is the quantization error calculated as follows:
=
C : Speed of light in a vacuum = 3
× 10
8
(m/s)
t : Finest time resolution 10
× 10
-9
(s)
NVP : Nominal Velocity of Propagation
(Signal propagation speed as a percentage of the speed of light in
a vacuum)
In the default case with NVP value of 0.684, ≅ 1.
Theory of Cable Length Measurement
Measurement Accuracy
Refer to "Section Accuracy" (p.39) for details
about rdg.
M
odel 3665-20 LAN CABLE HiTESTER
Terminato
r
Cables being
checked
Near End
Far End
Pulse
L
=
C
× T × NVP
2
χ
χ
χ
C × t × NVP
2
χ