RIDGID SeekTech SR-20 - Manual (Page 16)

Ridge Tool Company 
Tools For The Professional TM
seekTech sR-20
Operating Tips for Passive Line Tracing
1. In Passive Locating if you are looking for a known line,
be sure you are using the best frequency for the line
in question. This may be, for example, be 50 Hz (1) for
a power line, or it may turn out that 50 Hz (9) produces
a more reliable response on a particular line.
2. If seeking a cathode-protected pipe in Passive Mode,
use higher-frequency (greater than 4 kHz) to pick up
harmonics.
3. Remember that pipes can carry currents that will
show up on a Passive Trace as well as cables will; the
only guarantee of a locate is inspection.
4. In general, Passive Trace locating is less reliable than
Active Line Tracing because Active Line Tracing offers
the positive identification of the signal from the
transmitter.
5. Especially in Passive Line Tracing, knowing that you
have found something is not the same as knowing
what you have found. It is essential to use all the
indicators available, such as Measured Depth, Signal
Strength, etc., to confirm a locate. If it is possible to
find part of a passively-located cable, it can then be
energized using a transmitter and positively traced.
6. While Passive Line Trace is most often used on
50/60 Hz power lines, other cables such as phone
lines, CATV lines, etc., can be energized by transient
radio frequencies in the region and may appear on
Passive Line Trace searches.
Sonde Locating
The SR-20 can be used to locate the signal of a Sonde
(transmitter).
IMPORTANT! Signal strength is the key factor in determining
the Sonde’s location. Take care to maximize the Signal
Strength prior to marking an area for excavation.
The following assumes that the Sonde is in a horizontal pipe,
the ground is approximately level and the SR-20 is held with
the antenna mast vertical.
The field of a Sonde is different in form from the circular field
around a long conductor such as a pipe or cable. It is a dipole
field like the field around the Earth, with a north Pole and a
south Pole.
Figure 25: Earth’s Dipole Field
In the Sonde’s field, the SR-20 will detect the points at either
end where the field lines curve down toward the vertical,
and it will mark these points on the map display with a “Pole”
icon ( ). The SR-20 will also show a line at 90 degrees to the
Sonde, centered between the Poles, known as the “Equator”,
much like the Equator on a map of the Earth if the planet
were viewed sideways (See Figure 25).
Note that because of the SR-20’s Omnidirectional antennas,
the signal stays stable regardless of orientation. This means
the signal will increase smoothly when approaching the
Sonde, and decrease smoothly moving away.
NOTE: A Pole is found where field lines turn vertical. The
Equator occurs when the field lines are horizontal.