3M 2550 Manuale Utente

78-9000-0192-2 Rev C 

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Step 8.  When the bar graph fills toward the left (red-and-white-striped Fault Finding 

Direction Indicator [8] (See illustration above.)) side of the display, the fault 

has been passed and is now behind the operator. Move back, inserting the 

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 Earth Contact Frame every few inches, until the arrows alternate back to 

green. Mark the point beneath the center of the Earth Contact Frame. Turn the 

Earth Contact Frame 90 degrees and insert into the ground over the previously 

marked point. Move the Earth Contact Frame to the left and right (following 

the directions of the green and red indicator arrows). When the arrows reverse a 

third time, turn the Earth Contact Frame 90 degrees again. Pinpoint the fault by 

moving the Earth Contact Frame in the direction of the green and red indicator 

arrows. The fault is located beneath the center of the Earth Contact Frame when 

the arrows change from one side to the other this time.

Step 9.  To verify the fault location, insert the Earth Contact Frame’s red-and-white-

striped probe directly on the spot identified above. Pivot the Earth Contact 

Frame in a circle around the red-and-white-striped leg re-inserting the green-

banded leg in the ground every few degrees of the circle (See figure below). 

The arrow should always point toward the left (red) indicating that the fault is 

directly below the red-and-white-striped leg.

Step 10. After a fault is located and pinpointed, move the Earth Contact Frame about 

one Earth Contact Frame width away from the fault and insert it in the ground 

with the green-banded leg towards the fault. Compare the numeric signal 

level with the fault signal strength level reference indicated in the lower left 

box labeled REF. If the reading is within 12 dB of the fault signal strength 

reference, the operator has found the major fault. If the fault reading does not 

fall within 12 db of the fault signal strength reference reading, multiple faults 

may exist. The signal level of this secondary fault can be saved by pressing 

Fault 1 [SK] or Fault 2 [SK]. The fault with the highest reading will be the 

primary fault.