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78-9000-5020-0 Rev C
Use Induction Peak (Ind Pk) 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 (Spl Pk) or Directional Peak (Dir Pk) modes. Special (single) Peak (Spl
Pk) 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 of the transmitter, the transmitter
will automatically turn on the internal antenna, and the last frequency used (8 kHz, or
higher) will broadcast in induction mode.
The induction frequency can be changed by pressing the Trace 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, have the gain set between
78-84% and have the receiver in Induction Peak (Ind Pk) mode when starting the
sweep. 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 (Area) Induction Mode Locating
Sweeping an area with the 3M™ Dynatel™ Locator 7500 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 accuracy along with an effective
identification. There are two main types of “no access” or “blind” Induction Sweeps;
Passive Sweeps:
These require only the use of the Receiver with passive frequency
detection capability. This method uses existing external signal sources, such as
50 Hz/60 Hz for electric power, 15 kHz to approximately 30 kHz for low frequency radio
signals, 100 Hz / 120 Hz CPS for impressed current Cathodic Protection signals and the
less commonly occurring CATV signal of 31.25 kHz NTSC with CRT TV turned on.
Active Sweeps:
These require both the Receiver and Transmitter with Induction
capability. This method refers to using a 3M Dynatel transmitter as the signal source
through induction, instead of relying on passive frequencies that may exist on the buried
conductor or metal pipe. Active Induction allows for detecting buried cables and metal
pipes in the absence of passive signals and at deep depths and short sections. 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 7500E Series transmitters provide four induction frequencies: 8 kHz, 33 kHz,
82 kHz and higher and 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.
C. Passive Sweeps
Select Special (single) Peak (Spl Pk) mode on the receiver and then select the frequency
(source; for example, power, LF, etc.) to be traced. Passive sweeps at power frequency
will detect buried power cables and conductors carrying 50 Hz/60 Hz power signal in the
ground. Other passive sources exist, such as Cathodic Protection, LF and CATV cable
(with NTSC TV CRT turned on).