An improved signal processor for the ultrasonic dimension gauge.

The flip-flop producing a pulse proportional to the transit time of an ultrasonic burst between two piezoelectric crystals was often reset by transmission artefacts in sonomicrometers. A design improvement was made. The insertion of two monostable vibrators and one nand gate corrected the resetting caused by transmission artefacts. The new design produced a flip-flop pulse that was proportional to the transit time of the ultrasonic burst through the aorta. Ascending aortic diameter was monitored in unanaesthetised dogs for 6 to 8 weeks using the new design.