3M 2573, 2550 manual Induction Method, Non-SweepingPassive Induction Mode Locating

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 field. 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 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. 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 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 [T-6].

−− 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 (Ind Pk) 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 (Ind Pk) mode when sweeping distance between the transmitter and receiver is 25–60 feet (7.6–20 m). Beyond 60 feet (20 m) 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.

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