Ridgid SeekTech SR-20 User Manual download pdf (Page 15)

Ridge Tool Company

Tools For The Professional

seekTech sR-20

Passive Line Tracing

In passive mode, the SR-20 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 reason 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.

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.

In short, frequencies can show up on buried conductors in

numerous ways, and these can be picked up passively, if the

elds are strong enough.

Select a Passive Line Trace Frequency (

or icon).

Figure 24: 60

9th

Hz Passive Trace Frequency

2. The SR-20 has multiple Passive Line Trace

frequency settings. Power frequencies (identied

with the power icon

) are used to locate signals

generated as the result of power transmissions,

usually 50 or 60 Hz. To reduce the eects of inherent

noise from line-load or neighboring devices the SR-20

can be set to locate various multiples (or harmonics)

of the base 50/60 Hz frequency up to 4,000 Hz.

The 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

Hz countries) frequency settings are particularly

useful for pipelines that have been equipped with

cathodic protection using rectiers.

As in Active Line Tracing, the Tracing Line will reect distortion

in the detected eld by appearing unfocused or cloudy in

proportion to the distortion. This “distortion response” is

useful in recognizing when the eld being traced is being

distorted by other elds of metallic objects in the vicinity.

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 nding 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

extremely weak, the Measured Depth will generally read too

DEEP and the actual buried depth may be MUCH shallower.

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Ridgid SeekTech SR-20 User Manual Page 15

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