Patent ID: 8776878

Claim:
A downhole tool deployable into a borehole of a downhole formation, the borehole having downhole fluid, wherein the downhole tool comprises a sensor for determining at least one downhole parameter of the wellsite, the sensor comprising: a pad comprising insulation; at least one return positionable in the insulation, the at least one return adapted to exchange a current with a power source, wherein the at least one return comprises a first portion and a second portion; a fluid zone comprising the first portion of the at least one return and a mud button positionable in the insulation a distance from the at least one return, the mud button exchanging current with the first portion of the at least one return; wherein the fluid zone comprises a recess, and wherein the mud button is positioned in the recess; at least one guard for limiting at least a portion of the current flowing between the mud button and one of the at least one returns through the pad, each of the at least one guards positionable between the mud button and one of the at least one returns; and a formation button positionable in the insulation, the formation button exchanging current with the second portion of the at least one return, wherein the formation button is positioned on an outer surface of the pad such that the current passing between the at least one return and the formation button passes through the downhole fluid and the downhole formation, and wherein the mud button is closer to a longitudinal axis of the downhole tool compared to the formation button; and wherein the mud button and the fluid zone are positioned such that a majority of the current passing between the first portion of the at least one return and the mud button passes through the downhole fluid whereby the current exchanged with the mud button generates a measurement of the downhole fluid.