SeekTech
Passive Line Tracing
In passive mode, the
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
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 
) 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
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: 609th 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.
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