| CPC G01D 5/2291 (2013.01) [G01B 7/003 (2013.01)] | 9 Claims |

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1. A magnetic sensing tool (“MST”) for detecting the approximate axial location of a target tool having an outer diameter, comprising:
a generally cylindrical housing comprising a central longitudinal axis and an inner diameter greater than the outer diameter of the target tool; and
a plurality of coils disposed about the housing, comprising:
an upper receiver coil;
a lower receiver coil;
a central transmitter coil connected to a power source configured to generate a voltage in the transmitter coil; and
a sensor configured to measure the voltage within each of the plurality of coils;
wherein the plurality of coils are configured such that:
when there is no target tool disposed within the housing, a first baseline voltage is induced in the upper receiver coil and a second baseline voltage is induced in the lower receiver coil; and
the presence of a target tool within the housing causes the induced voltage in at least one of the upper and lower receiving coils to decrease from the baseline voltage.
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