RIDGID SeekTech ST-305 Operator's Manual download pdf (Page 15)

Ridge Tool Company ● Elyria, Ohio ● U.S.A www.seektech.com 13

SeekTech ST-305 Line Transmitter

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:

1. Power transmitter on.

2. Set frequency output to 33kHz.

3. Set power level to high power.

4. Power receiver on.

5. Set to receive 33kHz.

6. Move receiver 12 inches from transmitter.

If the inductor core is undamaged, the receiver

should show a Signal Strength reading larger than

2000.

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.

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 transmitter 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.

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 resistance” and adds to the resistance in

the circuit in proportion 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 consequent 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

kilohertz (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

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RIDGID SeekTech ST-305 Operator's Manual Page 15

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