Patent ID: 8028563

Claim:
Apparatus for generating a pressure pulse of known magnitude comprising: a first chamber filled with an incompressible fluid; a second chamber filled with a gas, the second chamber hydraulically linked with the first chamber; a third chamber filled with an incompressible fluid, the third chamber hydraulically linked with the second chamber; a fourth chamber filled with an incompressible fluid, the fourth chamber hydraulically linkable with the third chamber via a first valve; a fifth chamber filled with an incompressible fluid connected to the probe the fifth chamber hydraulically linkable with the fourth chamber via a second valve; means for sensing pressure in the third chamber; and means for sensing pressure in the fourth chamber; means for sensing pressure in the fifth chamber or the probe, whereby a pressure pulse of a magnitude corresponding to the sensed pressure differential between fourth chamber and the fifth chamber with the second valve closed can be generated by opening the said second valve, with the first valve shut in order to isolate the first, second and the third chamber from the fourth and fifth.