Patent ID: 7878244

Claim:
An apparatus, comprising: a downhole tool configured for conveyance within a wellbore extending into a subterranean formation, the downhole tool comprising: a sampling probe configured to couple with a sidewall of the wellbore adjacent the formation and draw a fluid sample from the formation; a displacement unit assembly comprising: a plurality of chambers including two first chambers and two second chambers; and first and second pistons coupled to a shaft for synchronous movement upon movement of the shaft, wherein the first piston fluidly isolates the first chambers relative to one another, and wherein the second piston fluidly isolates the second chambers relative to one another; a first flowline fluidly coupled to each of the first chambers; a second flowline fluidly coupled to each of the second chambers; a metering valve fluidly coupled between two of the plurality of chambers, wherein the metering valve is configured to incrementally choke flow therethrough between fully open and fully closed; and a fluid hydraulics block fluidly coupled between the sampling probe and the first and second flowlines.