RIDGID SeekTech ST-305 Operator's Manual page 14

SeekTech ST-305 Line Transmitter
Figure 12: ST-305 in Inductive Mode at 33 kHz
5. Lower frequencies couple poorly. Therefore,
the ST-305 transmitter in Inductive Mode
defaults to 33 kHz. Higher power is usually
required for a clear signal in Inductive Mode.
Pressing the power key will cycle through the
three available power levels: 1 kHz, 8 kHz,
and 33 kHz.
NOTE: If using the ST-305 in Inductive Mode, be
certain to switch Inductive Mode off if you are
going to use the unit in direct connect mode. Air
coupling can create very confusing signals if you
inadvertently have the unit set to Inductive Mode
and are trying to use it in direct connect mode.
Coupling through Air
When a line transmitter is set to Inductive Mode, it
energizes a wire or pipe under it by emitting a wave
of energy rising and falling at the selected frequency.
This forms an electromagnetic field which induces a
current into the conductor (the pipe or wire)
underneath it. The field builds and collapses at the
frequency generated by the transmitter.
A secondary field is set up around the pipe or wire by
the current induced into it. This secondary field is
normally round in shape, just as it would be if the
transmitter were connected directly. But the primary
field from the transmitter, which does the inducing, is
not round, and is not the same as the field set up on
the pipe or wire.
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Figure 13: Air Coupling
Near the transmitter, the receiver reads on the
local dipole field around the transmitter.
The field generated by the transmitter has a shape
something like a football. When the transmitter is
sitting on the 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 (8-10m)
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.
Ridge Tool Company ● Elyria, Ohio ● U.S.A