Technical data

280 Chapter 10
Distance to Fault
Measuring Distance to Fault
Distance to Fault
measurement distance is set using the [Start Distance] and the [Stop Distance]
menu keys on the [Freq/Dist/Calibrate] menu. In this mode, the displayed and
measured distances are the same. There are always 256 measurement points
across the distance you set, so adjusting the distance settings allows you to
display the maximum resolution for the portion of the cable you are testing. The
disadvantage is that the start and stop frequencies are automatically set and may
limit the test set's ability to sweep through filters or lightning protectors. This
mode is best used for checking a cable that has no frequency limiting devices.
Example 1: If you set [Start Distance] to 0 m (0 ft) and the [Stop Distance] to
60 m (197 ft), and you specify 256 Data Points, the instrument automatically
selects a [Start Freq] of 375 MHz and a [Stop Freq] of 659.8 MHz.
Example 2: If you again set [Start Distance] to 0 m (0 ft) and the [Stop Distance]
to 60 m (197 ft), and but this time you specify 1024 Data Points to give you
greater resolution, the instrument automatically selects a [Start Freq] of
375 MHz and a [Stop Freq] of 1.5142 GHz.
• Manual Frequency Range. When set to
Manual, you must specify the Start
Frequency
and the Stop Frequency, and the measured distance is worked out
from these frequencies. Generally, the typical start and stop frequencies you use
will result in a measured distance that will be larger than the distance over which
you want to look for faults.
NOTE The Measured Distance and the Displayed Distance can be different. The distance
over which the instrument has made its measurements, and which has been derived
from the frequencies you specified, is called the
Measured Distance. This is
displayed at the top right corner of the measurement screen.
The
Displayed Distance refers to that part of the entire Measured Distance that
you choose to display on your measurement screen. You set the
Displayed Distance
manually by pressing the [Start Distance] and the [Stop Distance] menu keys on the
[Freq/Dist/Calibrate] menu.
To help isolate faults over the length of interest, you can set a displayed distance
less than the measured distance. The displayed distance is set using the [Start
Distance] and the [Stop Distance] menu keys on the [Freq/Dist/Calibrate] menu.
Keep in mind that there are 256, 512, or 1024 measurement points across the
measured distance. The exact number of measurement points is set using the
[Data Points] key on the [Setup] menu. Therefore, the measurement points
across the chosen displayed distance will be a ratio of displayed distance to
measured distance times the number of points you have specified. The higher the
number of data points, the greater the measurement resolution.