Bird Technologies SH-362S-Manual - Manual (Page 68)

46
Distance to Fault (DTF) Measurement
This measurement will display the distance to a fault in a given length of cable. The
standard settings for this measurement are Start & Stop Distances, Distance Units,
Cable Velocity Propagation & Loss, and Smoothing. These settings can be adjusted
using either the thumbwheel or keypad.
Note: Changing the frequency span or the max distance will automati-
cally turn calibration off. Always set the frequency span or max distance
before calibrating the unit. The maximum distance measured is deter-
mined by the frequency span, the velocity of propagation of the cable
(V
p
), and the number of data points to measure these factors. This is dis-
cussed in the following paragraphs:
Distance - Normally when a frequency span is specified, the SignalHawk calculates
the maximum measurable distance. For this measurement, the distance to be
measured is entered, see “Start Distance” on page 47 and see “Stop Distance” on
page 48, and the SignalHawk calculates the frequency span. Use the DTF Wizard
to manually enter the cable length. See “Estimated Cable” on page 52.
Note: When the distance is entered manually, be sure to select the
data points before entering the max distance. See “Data Points” on
page 48.
Note: If a maximum distance is less than the total length of the cable
system, the trace may show a spike that is not a fault, but rather an
echo from the portion of the cable that is beyond the length chosen.
Such a spike is known as an alias. To avoid aliasing, always set the
Stop Distance to a value that is a few feet or meters greater than the
entire length of the cable system.
Data Points - If the number of data points increases, the measurable distance
increases. See “Data Points” on page 48.
Frequency Span - If the frequency span narrows, the measurable
distance increases.
Velocity of Propagation - The velocity of propagation is a characteristic of the cable
and is expressed as a percentage. Contact the cable manufacturer to get the velocity
of propagation value for the cable being used.