09/02-09   -   Press releases

Piezoceramics in ultrasonic flow meters

An ultrasonic flow meter is a device which will either measure the flow velocity, volume or mass flow of pure water, wash water, sewage, process liquids, oils, and other light homogeneous liquids. Piezoceramic transducers are used to detect the flow through a pipe by using acoustic waves or vibrations of a frequency.

Low dielectric and mechanical losses
Noliac Ceramics offers high quality piezo bulk/ monolayer transducers for ultrasonic applications and, thus, flow meters. PCM41 and PCM40 are low loss materials for high power applications. The low dielectric and mechanical losses (tgd, Qm) combined with high piezoelectric charge constant (d33) make them suitable for high power ultrasonic applications.

Depending on the shape and size of your flow meter, we will customize the component according to your specifications. We are able to manufacture all common monolayer piezoceramic shapes, such as discs, rings, tubes, rods, bars and plates including shear mode configurations. Additionally, we customize according to dimension tolerances as well as tolerances for dielectric and electromechanical properties

Ultrasonic flow rate measurement
The measurement of the Doppler effect and the propagation time are the two fundamental measurement techniques used in ultrasonic flow rate measurement. The piezo transducers used in each generate ultrasonic waves which are introduced into the liquid at an angle to the direction of flow.

With the Doppler principle, the phase and frequency shift of the ultrasonic waves which are scattered and reflected by particles of liquid are evaluated. The frequency shift between the wavefront emitted and received by the same piezo transducer is a measure of the flow speed.

The measurement of the propagation time is based on transmitting and receiving ultrasonic pulses on alternating sides, i.e. in the direction of flow and against it. Two piezo transducers operating as both transmitter and receiver are arranged diagonally to the direction of flow in an acoustic cell. Emission of the wave burst in the flowing medium (liquid or gaseous) causes a superposition of sound propagation speed and flow speed.

The flow speed is proportional to the reciprocal of the difference in the propagation times in the direction of the flow and in the opposite direction.

More information: http://www.noliac.com/Piezoceramics_in_ultrasonic_flow_meters-7913.aspx