Useful Information; Resistance And Impedance; Using High And Low Frequencies - RIDGID SeekTech ST-510 Operator's Manual

SeekTech ST-510 Line Transmitter
Figure 30: Adjusting LCD Contrast

Useful Information

Resistance and Impedance

A circuit has a certain resistance that is measured in
Ω
ohms ( ). Higher resistance reduces the amount of
current that can be put on an underground line at a
given voltage. (Current is equal to voltage divided by
resistance). Factors that affect resistance are
conductivity of the line itself, insulation material and
condition, breaks or faults in the line, and how well
the transmitter is grounded.
Grounding can be affected by soil conditions
(wetness or dryness, for example), length of
grounding stake, or how the line transmitter is
connected to the grounding rod. Improving the
ground connection is the quickest way to improve a
tracing circuit.
Note: It is difficult to set up a good ground
connection in extremely dry soil. This condition can
be remedied by moistening the soil around the
grounding stake.
Impedance is resistance which varies with AC
frequency. The measurement units in both cases are
the same, ohms. Impedance increases with the
frequency transmitted. Total "resistance" can include
impedance, and can be effected by inductance and
capacitance in the circuit and nearby metallic objects.
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Using High and Low Frequencies

Understanding the behaviour of different frequencies
under different conditions can be important in doing
effective and accurate locates.
In both direct-connect and inductive mode, the ST-
510 is essentially doing the same thing – imposing a
wave of traceable energy onto the target pipe or line.
This electrical energy rises and falls a certain number
of times per second, which in turn causes a magnetic
field to build and collapse around the conductor at a
regular rate. This rate is known as the frequency of
the generated current and of its consequent magnetic
field.
Frequency is expressed in terms of hertz (Hz), which
means cycles per second, or kilohertz (kHz), which
means thousands of cycles per second.
Low Frequencies
The ST-510 will generate frequencies as low as 128
hertz. Low frequencies are especially useful for
several reasons. First, they will travel farther at a
detectable level along a continuous pipe or wire
conductor than a high frequency will. Secondly, lower
frequency fields lose less energy to the area around
the conductor. If you can get a clear signal on your
receiver using a low frequency, it is generally
preferable because you will be able to trace it further
and it will tend to confine itself to the original
conductor more than a high-frequency signal will. But
a low-frequency signal is more likely to be interrupted
by gaps in the line, poor insulation or hidden by other
magnetic fields in the area. It is a "weaker" signal in
that respect. While it doesn't jump as readily onto
other lines, it will lose signal if traveling on a line with
poor insulation, bare-concentric cable, or bare pipe
exposed to earth, and will follow the path of least
resistance, which is not always the path intended by
the operator. This can make tracing the original
conductor difficult.
High Frequencies
The ST-510 will generate frequencies as high as 262
kilohertz. (European versions are limited to 93 kHz.)
There are certain conditions where only higher
frequencies will serve. High-frequency signals are
especially valuable when you are tracing a line that
has some sort of interruption—such as a gasket, or
decayed insulation – in the continuity of the