Filter
Top Products
20 www.seektech.com Ridge Tool Company Elyria, Ohio U.S.A
SeekTech SR-60
Passive Line Tracing
In passive mode, the SR-60 is looking for
electromagnetic “noise” that has found its way onto a
buried utility line by any available means.
Electromagnetic signals can get onto buried utility
lines in a variety of ways.
The most common way is by means of direct
connection to some signal source. All operating
electronic devices that are connected to AC power will
radiate a certain amount of electronic “noise” back
onto the power lines they are connected to. Examples
of such devices include computers, copy machines,
refrigerators, anything with an electric motor, TV sets,
air conditioning units, etc.
Another common way electromagnetic noise can get
onto the line is by way of induction that can operate
without any direct physical connection to the buried
line. In some areas for example, buried utilities act as
antennas for high powered, low frequency radio
transmissions (submarine navigational and
communication signals in the UK for example) and will
reradiate these signals. These reradiated signals can
be very useful for locating.
Similarly, buried lines that run side by side near each
other, particularly for longer distances will tend to
bleed signals onto each other. This effect is more
pronounced for higher frequencies. Due to coupling,
all metallic lines in an area may be energized.
Because of this, it is possible to locate lines passively,
but it is difficult to identify which line the locator is
tracing.
Pipes can also have 60 Hz signal randomly induced
into them by nearby power-line fields, and other
frequencies can be picked up on phone lines, for
example, from the energy of radio-broadcast towers in
the vicinity. In short, frequencies can show up on
buried conductors in numerous ways, and these can
be picked up passively, if the fields are strong
enough.
1. Select a Passive Line Trace Frequency
(
or icon).
2. Choose an orderly pattern of search that will
cover the area you are interested in.
3. Use the Tracing Line, Depth, and Signal Strength
to steer you to the lines which have that
frequency energizing them.
4. If possible, once you have found a target of
interest, find an accessible point and do an Active
Trace on it to confirm your results.
The SR-60 has multiple Passive Line Trace
frequency settings. Power frequencies (identified
with the power icon
) are used to locate signals
generated as the result of power transmissions,
usually 50 or 60 Hz. To reduce the effects of inherent
noise from line-load or neighboring devices the SR-60
can be set to locate various multiples (or harmonics)
of the base 50/60 Hz frequency up to 4,000 Hz.
(<4kHz setting).
The 50/60 Hz 9x multiple is the setting most
commonly used to locate 50/60 Hz signal. In well-
balanced high voltage electric distribution systems,
the 5x multiple may 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 cathodic protection using
rectifiers.
As in Active Line Tracing, the Tracing Line will reflect
distortion in the detected field by appearing un-
focused or cloudy in proportion to the distortion. This
“distortion response” is useful in recognizing when the
field being traced is being distorted by other fields of
metallic objects in the vicinity.
Figure 29: 60
9th
Hz Passive Trace Frequency
There are also two higher radio frequency bands
to help locate lines passively. They are:
• 4 kHz to 15 kHz (LF)
• 15 kHz to 35 kHz (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. Even more convenient is to use the
OmniSeek setting described below.