accurate pressure reading the procedure for obtaining a pressure reading continues with electrical signals of a chosen frequency or frequencies delivered to tool 60 these signals activate pulse device 70 at a corresponding mechanical frequency activation of pulse device 70 causes it to oscillate thereby imparting a rhythmic expansion and contraction of the volume of chamber 84 the rhythmic expansion and contraction of the volume in chamber 84 imparts pressure waves in the fluid this wave energy flows through the only point of discharge orifice 76 orifice 76 focuses the wave discharge into a concentrated beam because the pulsation frequency causes the fluid to resonate at a helmholtz frequency pulse device 70 efficiently transfers energy to the fluid discharge the near instantaneous result is a flow of wave energy expelled from the tool orifice 76 directs the wave discharge toward borehole wall 28 layered with mudcake 30 the fluid pulsations strike mudcake 30 flush away the mudcake 30 and thereby restore permeability to borehole wall 28 at this point electrical signals to the tool can stop and the fluid oscillation thereby ceases the necessary period is allowed for the hydrocarbons in formation 14 to pressurize tool chamber 84 the time period needed to pressurize chamber 84 will vary depending on factors such as the permeability of the formation and.