Patent ID: 7812506

Claim:
A fluid characteristic measurement device comprising: a piezoelectric/electrostrictive membrane type sensor including a ceramic base body having a thin diaphragm portion, a thick portion integrally provided on the peripheral edge of the thin diaphragm portion, and a cavity formed by the thin diaphragm portion and the thick portion so as to communicate with the outside, and a piezoelectric/electrostrictive element having a laminate structure arranged on the outer surface of the thin diaphragm portion of the ceramic base body and including a membrane-like piezoelectric/electrostrictive body and a pair of membrane-like electrodes between which the piezoelectric/electrostrictive element is sandwiched, the thin diaphragm portion of the ceramic base body being configured to vibrate in synchronization with the driving of the piezoelectric/electrostrictive element, wherein the piezoelectric/electrostrictive body contains an alkaline metal or an alkaline earth metal, and the electrodes contain gold or platinum; a power source which applies a voltage to drive the piezoelectric/electrostrictive element of the piezoelectric/electrostrictive membrane type sensor; electric constant monitor means for detecting the change of an electric constant accompanying the vibration of the thin diaphragm portion of the piezoelectric/electrostrictive membrane type sensor; and insulation resistance measurement means for measuring the insulation resistance of the pair of electrodes between which the piezoelectric/electrostrictive body is sandwiched in the piezoelectric/electrostrictive membrane type sensor.