Ultrasonics make compact flow meter
A novel vortex shedding flowmeter, which is only slightly wider than pipes to which it is attached, offers more proof against vibration than conventional designs that detect vortices using piezoelectrics.
The Keyence FD-V70 employs a triangular bar to induce the vortices, which are detected by an ultrasonic transmitter and receiver placed on opposite sides of the downstream channel. The company has found ways to make the device very narrow and, by usihng ultrasonic detection, avoid the spurious detection of external vibration.
The principle is applicable to any fluid flowing with a Renolds number greater than about 50, and because it is non-contact, is applicable to measuring flows of corrosive fluids or those that must not be contaminated – such as ultra-pure water used for semiconductor manufacture. Sensor heads are available in polyphenylene sulphide (PPS) or perfluoroalkoxy fluorocarbon (PFA). Models are available for flow rate ranges from 0.4 to 4 litres/minute up to 5 to 50 litres/minute. A linear LED display shows green to indicate instantaneous flow rate or red to show lack of flow.
