Fault Mapper Pro Model CA7026
11
4.7
Determining and Measuring Vp Values
Vp, or Velocity of Propagation, values are characteristic of each cable
type and brand. The Vp is used to measure the length of a cable and to
measure a fault location. The more accurate the Vp, the more accurate the
measurement result will be.
The cable manufacturer may list the Vp on their specification sheet or
may be able to provide it when asked. Sometimes this value is not readily
available, or the user may wish to determine it specifically to compensate
for cable batch variations or for special cable applications. This is quite
easy:
1. Take a cable sample of exact length increments (ft or m) longer than
60 ft (20m).
2. Measure the exact length of the cable using a tape measure.
3. Connect one end of the cable to the Fault Mapper Pro (see § 4.9).
Leave the end unterminated and make sure the wires do not short to
each other.
4. Measure the length and adjust the Vp until the exact length is displayed.
5. When the exact length is displayed, Vp is established.
4.8
Adjusting the Vp Value
To adjust the Vp, press and hold the
TDR /
button and press the
TEST /
button to enter the setup mode. Release both buttons. Press the
TEST /
button until the pointer (
>
) is next to Vp.
Next use the
and buttons to adjust the Vp to the desired percentage.
Press the
TDR /
button to exit the set up mode.
