Patent ID: 8333568

Claim:
An apparatus for pumping fluid comprising: a housing having an exterior surface and an interior surface, the interior surface defining a cylindrical chamber having a first end wall and a second end wall, the second end wall having a plunger opening through which a plunger is reciprocal in the chamber to cause fluid to enter the chamber through a fluid inlet opening and to discharge fluid from the chamber through a fluid discharge opening, wherein the housing has an integrally formed cavity recessed into its exterior surface to provide a transducer surface which is radially spaced from the interior surface of the housing and which is disposed between said first end wall and the end of the plunger when the plunger is at a maximum displacement of a compression stroke, and wherein a strain sensor is affixed to the transducer surface to measure deformation of the housing resulting from differences in fluid pressure within the chamber, the strain sensor producing a first signal indicative of the transducer surface assuming a first position when the chamber is at low pressure and producing a second signal indicative of the transducer surface assuming a second position when the chamber is at high pressure.