Patent ID: 8726726

Claim:
A dynamic pressure sensor unit ( 5 A) for a logging tool for hydrocarbon wells with a piezoelectric element ( 5 ) in a sensor sleeve ( 3 ), wherein the piezoelectric element ( 5 ) is a tubular element with an inner and an outer diameter; the sensor sleeve ( 3 ) has an inner area with an inner diameter greater than the outer diameter of the tubular piezoelectric element ( 5 ); the piezoelectric element is situated in the inner area of the sensor sleeve ( 3 ), whereby a gap ( 12 ) with a gap thickness is formed between the inner area of the sensor sleeve ( 3 ) and the piezoelectric element ( 5 ), defining an annular volume; a dynamic pressure transmitting liquid in said annular volume; characterized in a pressure control system for said a dynamic pressure transmitting liquid to prevent pressure variations on the piezoelectric element ( 5 ) when the sensor unit ( 5 A) is exposed to variations in static pressure, temperature or other ambient conditions, wherein the pressure control system for said dynamic pressure transmitting liquid includes at least one seal is placed in a circumferential notch in the sensor sleeve ( 3 ), and wherein said notch is dimensioned to allow the seal to move in the notch in an axial direction in relation to the sensor sleeve while maintaining a seal between the sensor sleeve ( 3 ) and the piezoelectric element ( 5 ) whereby pressure is controlled by allowing the seal to adjust the volume of the dynamic pressure transmitting liquid in relation to the gap thickness and thermal oil expansion.