calculated those skilled in the art will recognize that it is quite difficult to control the pressure pulse with hydraulic lines filled with brine an embodiment of a mechanism for reliably generating a pressure pulse of known magnitude is illustrated in fig3 the illustrated pulse generator includes an isolation valve v 1 that may be actuated during testing in response to commands from either the control unit or the tool itself opening the isolation valve allows the brine in chamber 312 to hydraulically communicate to an air filled chamber 302 through a floating piston 308 hydraulic oil in chamber 306 may be pumped on one side of the floating piston 304 which has stops on either side a second piston 308 separates the air from the brine in a brine chamber 310 and the brine line chamber 312 to the probe the second piston also has two stops one of which it shares with the first piston in order to prepare to generate the pressure pulse isolation valve v 1 is open and valve v 2 is closed valve v 2 should be as close to the probe as practical initially the pressure is built in the probe line by pumping hydraulic.