78-9000-5020-0 Rev C 25
3. Induction Method
If you cannot make a direct connection, or use the 3M™ Dyna-Coupler clamp to apply a
locating signal on the target, use the induction method. When nothing is plugged into the
Output Jack [T-6] of the transmitter the unit will be placed into induction mode when it
is turned on. This method uses the internal coil of the transmitter to generate a magnetic
eld. This is the least preferred method of applying a signal on a target conductor because
it can easily be picked up by other non-target conductors in the area. However, it is the
preferred method of applying a signal to multiple cables/pipes in the same trench and for
the “two-person sweeping” application.
3M Dynatel™ Transmitters provide a choice of induction frequencies and output power
levels. Higher induction output power levels are needed for detecting deeper depths and
longer ranges. The 7500 Series transmitters provide four induction frequencies:
7550/7573 8 kHz, 33 kHz, 82 kHz, 200 kHz
7550E/7573E (International) 8 kHz, 33 kHz, 82 kHz, 133 kHz
The induction frequencies have three output power settings up to 12W. The 82 kHz and
higher frequencies are commonly used for deeper cables/pipes and the lower frequencies
are used to give longer locate distances. The 8 kHz (low frequency) induction helps in
locating shallow facilities, such as risers.
The following sections review Non-sweeping and Sweeping (Area) methods used with
the Induction Mode. The Non-Sweeping method is utilized when a specic target
requires path tracing. The transmitter remains stationary in-line over the target and the
path is traced. The Sweeping method is utilized when a designated area needs to be swept
for non-specic targets, for example, all the buried pipes or conductors in the designated
area. Several sweeping methods will be reviewed.
A. Non-Sweeping Induction Mode Locating
• Position the transmitter over the target facility, with the hinge of the transmitter over
and in line with the cable/pipe path. Remove any cables from the Output Jack.
− Align the Induction Direction arrows on the transmitter with the target conductor.
• Turn on the transmitter, select the frequency and select high output or maximum
output power level for best signal-to-noise ratio.
• Trace the signal path with the receiver using the Induction Peak (Ind Pk) mode.
The Induction Peak mode of the receiver is a mode in which the upper antenna of the
receiver is tuned to minimize distortion from the magnetic eld of the transmitter.
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