Balance Control; Velocity Factor - Megger TDR1000 Manuel Utilisateur

Balance Control

Without Balance Control (point 2 in the User Controls and Display section) the transmitted pulse would be visible at the beginning of the trace,
swamping any reflections within the pulse length (the dead zone). The balancing circuit attempts to match the characteristic impedance of the
cable under test to produce an equivalent pulse. Subtracting this equivalent pulse from the transmitted pulse effectively removes the dead zone
and allows cable features much closer in to be detected.
NOTE: In many cases, it will be impossible to completely null the transmitted pulse.

Velocity Factor

The velocity factor is the scalar that is used to convert the measured time interval into an actual length of cable. It can be displayed in one of
two ways: a ratio of the transmitted pulse speed to the speed of light, or as a distance per microsecond. When it is displayed as the distance
per µs (either m/µs or ft/µs) the velocity factor will be indicated as half the speed of the pulse in the cable. This is because the pulse in fact has
to go along the cable to the cable feature and back again which is twice the distance to the feature.
If the exact length of a piece of cable of the same type as the C.U.T is known and the reflection from the cable end is visible then a more
accurate value can be determined:
Locate the reflection caused by the end of the known length of cable with the instrument set on the shortest possible range to see the end of
the cable.
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