Sweeping Active Induction Mode Locating, Passive Sweeps

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, 33 kHz, 82 kHz or 200 kHz) will broadcast in induction mode.

The induction frequency can be changed by pressing the Trace [T-3] (Frequency [T-3] on 2550) button on the transmitter. For best results, the receiver should be at least 25 feet (7.6 m) 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 (Active) Induction Mode Locating

Sweeping an area with the 3M™ Dynatel™ Locator 2500 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 60 Hz/50 Hz for electric power, 15 kHz to approximately 30 kHz for low frequency radio signals, 120 Hz / 100 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 2500 Series transmitters provide four induction frequencies: 8 kHz, 33 kHz, 82 kHz and 200 kHz and three output power settings up to 12W. The 82 kHz and 200 kHz 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 60 Hz/50 Hz power signal in the ground. Other passive sources exist, such as Cathodic Protection, LF and CATV cable (with NTSC TV CRT turned on).

78-9000-0192-2 Rev C