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Sound Velocity/Density SensorSensors and Ultrasonics |
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[Sensors and Ultrasonics] [IAP-Homepage]
The principle of calculating two unknown physical parameters of a layered resonator out of two quasiharmonic serie s resonance frequencies is applied to the density and sound velocity sensor.
The sensor consists of two piezoelectric plates vibrating in thickness extensional mode. The liquid to be measured is confined between these two plates. The mechanical displacement of the vibrating plates is even symmetrical with regard to the plane of symmetry. The liquid volume between the piezoelectric plates is terminated by an inlet and an outlet pipe. The resonant sensor element is covered by an aluminum block hous ing that, in connection with a Peltier element and two platinum resistance microthermometers in the inlet and outlet, respectively, functions as a compact thermostat. The sensor can be used in flow-through mode with continuous monitoring of the density and the sound velocity of the liquid, or in batch mode.
The primary measurands are two appropriately choo sen quasiharmonic resonance frequencies of the composite resonator filled with the liquid under test. The calculation of the liquid's density and sound velocity from two quasiharmonic frequencies is based on the solution of the fundamental piezoelectric equations using the one-dimensional treatment of layered piezoelectric structures. Taking advantage of the symmetric geometry, the computational effort is significantly reduced by substituting the three layer model by an equivalent two layer model, o btained by virtually cutting the structure into two equal halfs.