Appeal No. 96-2194
Application 08/042,292
parts of a plurality of closed current loops, which means a
substantial amount of wire length is required that is not
actually used for guidance.
Houskamp solves these and other problems by using a
buried guidewire wire which generates an AC electrical field
instead of an AC magnetic field. Referring to Figure 9, this is
accomplished by connecting one end of the wire to one terminal of
an AC voltage source 190, with the other terminal being connected
to the ground. The current flow in the wire is substantially
less than in a magnetic field system, thereby permitting the wire
to be formed of a more flexible material, such as materials
containing carbonized rubber (col. 9, lines 35-38). The electric
field strength can be detected by a probe 206 and voltmeter 202
(col. 8, lines 2-6). Referring to Figure 10 and to column 8,
lines 21-34, a capacitor 218 connected between voltmeter 202 and
ground 220 is selected to be several times larger than the
inherent capacitance 216 between the probe and wire 194. Figure
11 shows a pair of voltage probes 222 and 224 for providing the
inputs to either of the processing circuits shown in Figures 12
and 13, which generate a steering error signal on line 242
(col. 8, line 35 to col. 9, line 8).
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Last modified: November 3, 2007