78-8130-6151-8 Rev G
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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 (12 Watt transmitter only.)
The following sections review Non-sweeping and Sweeping (Area) methods used
with the Induction Mode. The Non-Sweeping method is utilized when a specific 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-specific targets, for example, all the buried pipes or conductors in the
designated area. Several sweeping methods will be reviewed.
A. Non-Sweeping (Passive) 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 max output
level for best signal-to-noise ratio.
•
Trace the signal path with the receiver using the Induction Peak 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 field of the transmitter.
Use Induction Peak mode when sweeping distance between the transmitter and receiver
is 7.6–20 m (25–60 feet). Beyond 20 m (60 feet) you can also use the Special (single)
Peak or Directional Peak modes. Special (single) Peak can be used for maximum
detection depth and range (needed for deep conductors and metal pipes), but would
require increased sweep distance separation between the transmitter and receiver.
Note: If nothing is plugged into the Output Jack [T-6] of the transmitter, the
transmitter will automatically turn on the internal antennae, and the last frequency
used (8 kHz (12 Watt transmitter only), 33 kHz or 133 kHz) will broadcast in induction
mode.
The induction frequency can be changed by pressing the Frequency button on the
transmitter. For best results, the receiver should be at least 7.6 m (25 feet) away from
the transmitter to begin tracing the target path and have the gain set between 78-84%
when starting the sweep. This is used to establish a baseline gain threshold prior to
starting a sweep. When crossing a target pipe or cable, the bar graph will close and
the signal strength and audio response will increase. Attempting to trace the target
close to the transmitter may lead to false indications due to the receiver detecting the
large magnetic field radiating from the transmitter.
B. Sweeping (Active) Induction Mode Locating
Sweeping an area with the 3M™ Dynatel™ Advanced Locator 2200M Series allows the
location of multiple metallic cables and pipes buried in an area without direct connect
or coupler access to the cable or pipe. This approach is effective before any excavation
takes place. Note that when specific buried objects need to be identified, it's important
to use the direct connect or coupler method for applying the signal. This will help limit
the applied locate signal to a specific facility that provides more position and depth