The piezoelectric pick up element is situated in a casing, said {HEAD ~ casing} being fixed to {TAIL ~ a hollow body} being tested as by a strap encompassing at least partly both the casing and the tested hollow body 
fixed to
The piezoelectric pick up element is situated in a casing , said { HEAD ~ casing } being fixed to { TAIL ~ a hollow body } being tested as by a strap encompassing at least partly both the casing and the tested hollow body
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH