- 12 -
for an abrupt drop in the signal (as shown by the null in Figure 18) that will occur when the lower sensor,
located 1-1/2 inches from the end of the locator, is directly over the stake. Any variation in the position of
the locator will produce an abrupt rise in the frequency of the signal.
Figure 18. Placement of Locator while Searching along a Chain Link Fence
Locating Valve Boxes
Both the valve and its casing, when iron, provide strong magnetic
fields which make them easy to locate. Plastic enclosures
containing magnets are easily located at depths of 6 feet or more.
Figure 19. Locating Valve Boxes and Casings
Locating Cast-Iron Pipes
As illustrated in Figure 20, cast-iron pipes produce the strongest magnetic signals at their joints.
Figure 20. Signal Patterns Provided by Cast-Iron Pipes
Summary of Contents for GA-92 XT
Page 19: ... 19 ...
