14
The trailing microphone is near the fault and should be left were it is. Move the lead
microphone back ¼ inch at a time. When both directions to fault LED’s light up, the
fault is centered between the two microphones. This spot is called the “NULL”
The fault is equal distance from each microphone, but this could be off to one side of
the cable route.
VERIFYING THE FAULT’S LOCATION
The final step needed to verify the fault location is the “90 degree WALK AROUND”.
Keep in mind that “DEAD INCH” accuracy can only be obtained if the “NULL” reading
is found in both the IN-LINE locate and the ACROSS THE CABLE locate.
See Figure
10 .
One microphone is placed directly over the “NULL” point or position of the fault. This
microphone will be called the PIVOT MICROPHONE. Move the other microphone
around the pivot microphone and take four ( 4 ) readings.
a. 30” up the cable route.
b. 30” down the cable route.
c. 30” off to one side of the cable route.
d. 30” off to the other side of the cable route.
This will provide readings on all four sides of the fault at 90 degree intervals. The
direction to the fault LED will show which microphone received the thump first.
Figure 10
What was thought to
be the cable route
What was thought to
be the cable fault
Where microphones
were placed for 90°
walk around
