Ridgid SR-60 User Manual download pdf (Page 22)

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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.

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