High Voltage Indicator; Useful Information; Resistance And Impedance; Using High And Low Frequencies - RIDGID SeekTech ST-305 Operator's Manual

ground, roughly half of that field extends below it� The
ends of the "football" extend out past the central axis of the
transmitter�
If the receiver is within this field, it will read clearly and well
on it, rather than on the field around the pipe or wire being
traced� The transmitter and the receiver will couple through
the air for a limited distance around the transmitter� This
problem does not occur with direct connection, and is not
important when using an inductive clamp� But it can be an
issue when using the transmitter in purely Inductive Mode
(i�e�, without a clamp)�
It is important to set up the transmitter, when using the
Inductive Mode, a good 20 or 30 feet [8 to 10 m] away from
the region where tracing occurs, and to be aware of the
difference between the transmitter's field and the induced
field being traced� They will both have the same frequency,
but the transmitter's field is limited to the region around the
transmitter itself�

High Voltage Indicator

Whenever the line transmitter encounters a live voltage on
the line higher than 62 VAC, it will flash a red LED at the top
of the keypad� Should this occur, carefully disconnect the
transmitter using high-voltage precautions�
NOTE: The inductor core of the ST-305 emits the signal
when the unit is transmitting in inductive mode� A hard hit or
a drop could possibly damage the core� To test that the core
is intact using a SeekTech SR-20 receiver:
• Power transmitter on
• Set frequency output to 33 kHz
• Set power level to high power
• Power receiver on
• Set to receive 33 kHz
• Move receiver 12 inches from transmitter
If the inductor core is undamaged, the receiver should show
a Signal Strength reading larger than 2000�

Useful Information

Resistance and Impedance

A circuit has a certain amount of resistance to current; this
is measured in ohms (Ω)� Higher resistance reduces the
amount of current that can travel along an underground
line� Factors that affect resistance in the transmitter circuit
are conductivity of the line itself, breaks or faults in the line,
insulation problems with the line, and how well the transmit-
ter is grounded� (Poor grounding makes the return path of
the circuit more resistive)�
Grounding can be affected by soil conditions, length of
grounding rod, or how the line transmitter is connected to
the grounding rod� Good grounding improves the signal
by reducing the total resistance the transmitted current
encounters�
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SeekTech ST-305
Impedance is a form of resistance which is caused by a
back-force in the electrical field caused by alternating
current (AC)� Impedance can be thought of as "AC resis-
tance" and adds to the resistance in the circuit in propor-
tion to the frequency being used (i�e�, higher AC frequencies
add more impedance than lower ones)�

Using High and Low Frequencies

Understanding the behavior of different frequencies under
different conditions can be important in doing effective and
accurate locates�
In both direct-connect and Inductive Mode, the ST-305
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 conse-
quent magnetic field�
Frequency is expressed in terms of hertz (Hz), which means
cycles per second, or kilohertz (kHz), thousands of cycles
per second�
Low Frequencies
The ST-305 will generate frequencies as low as 1 kilohertz�
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 dissipate 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-305 will generate frequencies as high as 262 kilo-
hertz (93 kHz in European version)� 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
conductor� The reason is that a high-frequency signal can
"jump" some barriers and continue without dissipating as
much signal as a lower frequency would�
A high-frequency signal can also be valuable in getting a
signal on a receiver when there is a poorly grounded circuit,
compared to the signal the same receiver will detect at a
lower frequency� While all currents tend to follow the path
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