Pulse Widths - Megger TDR1000 Manuel Utilisateur

Locate the start of this reflection as described in the Operation section of this manual.
Adjust the velocity factor until the correct cable length is shown.
The measurement of the distance to the fault can now be made with more confidence that the measurement will be correct. The ability of the
instrument to accurately measure the distance to a cable feature relies on the velocity factor being correct, any errors in the velocity factor are
directly proportional to distance measurement errors.

Pulse Widths

The TDR1000 pulse widths range from 7 ns to 3 µs to overcome signal attenuation and enable the instrument to see further down a length of
cable. In distance terms for the size of the transmitted pulse, this represents a transmitted pulse from as small as 1.4m to 602m! (This assumes
a velocity factor of 0.67.) Without Balance Control, this would be an enormous dead zone, but with the instrument correctly balanced, faults
can be seen well within the pulse width.
As the measured distance is taken at the start of the reflected pulse, the size of the pulse width does not affect the accuracy of the
measurement. However, if the first feature does not give a complete reflection such that the instrument can see beyond it to a second feature,
the ability to discern between features is affected by the pulse widths. If there are multiple features, the instrument can only fully discern
between them if the features are more than the pulse width apart. Hence, for discerning multiple features, the instrument should be used with
the shortest range, and so smallest pulse width, that can see both features (refer to the pulse width table in the specification).
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