Operating Tips For Passive Line Tracing; Sonde Locating - RIDGID SeekTech SR-20 Operator's Manual

work better. The 100 Hz (in 50 Hz countries) and 120 Hz
(in 60 Hz countries) frequency settings are particularly
useful for pipelines that have been equipped with ca-
thodic protection using rectifiers.
3. There are also two additional radio frequency
bands to help locate lines passively. They are:
• 4kHz to 15kHz (LF)
• > 15kHz (HF)
The Radio Frequency and <4 kHz bands can be useful in
discriminating when tracing in a noisy environment. They
are also very helpful in finding lines on blind searches.
When searching over a wide area where the location of
targets is unknown, one useful approach is to have
multiple frequencies selected for use and to check the
area at a number of frequencies in sequence looking for
meaningful signals.
In general, directly connected Active Line Tracing is
more reliable than Passive Line Tracing.
WARNING
In Passive Line tracing, or when signals are ex-
tremely weak, the Measured Depth will generally
read too DEEP and the actual buried depth may be
MUCH shallower.

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 60 Hz (1)
for a power line, or it may turn out that 60 Hz (9) pro-
duces a more reliable response on a particular line.
2. If seeking a cathode-protected pipe in Passive Mode,
higher-frequencies (greater than 4kHz) may also pick
up harmonics.
3. Remember that pipes can carry currents that will
show up on a Passive Trace as well as cables; 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 know-
ing 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 en-
ergize using a transmitter and positively trace.
6. While Passive Line Trace is most often used on
50/60Hz 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) in a pipe, so that its location can be identi-
fied above ground. Sondes can be placed at a problem
point in the pipe using a camera, push rod, or cable.
They can also be flushed down the pipe. A Sonde is
often used for locating non-conducting pipe and conduit.
IMPORTANT! Signal strength is the key factor in
The following assumes that the Sonde is in a hori-
zontal 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 26 – Earth's Dipole Field
In the Sonde's field, the SR-20 will detect the points at ei-
ther end where the field lines curve down toward the ver-
tical, and it will mark these points on the map display with
a "Pole" icon (
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 27).
Note that because of the SR-20's Omnidirectional an-
tennas, the signal stays stable regardless of orientation.
This means the signal will increase smoothly when ap-
proaching the Sonde, and decrease smoothly when mov-
ing away.
Ridge Tool Company
SeekTech SR-20
determining the Sonde's location.
Take care to maximize the Signal
Strength prior to marking an area for
excavation.
). The SR-20 will also show a line at 90
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