ABSTRACT
In building a flowmeter based on Karman’s principle, the manufacturer usually selects an obstruction width that is one-quarter of the pipe diameter. A flow-sensitive detector can be either a heated thermistor element or a spherical magnetic shuttle. The types of detectors that are in use as of this writing and the approximate number of manufacturers marketing them are listed below: mechanical, thermal, ultrasonic, strain gauge, capacitance, and piezoelectric. The principal features include no moving components, fixed calibration based on the geometry of the housing, linear digital or analog output, and good rangeability. The oscillating vane meter is limited to use on clean and cold liquids, and it is likely to require maintenance due to the continuous motion of the oscillating vane and the associated bearing components. Installation considerations, including straight pipeline requirements, are similar to those of regular vortex shedding flowmeters.
